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PubMed1998

Sex-specific selection on time to remate in Drosophila melanogaster.

Female Drosophila melanogaster were artificially selected for fast and slow time to remate (denoted 'high' and 'low' selection regimes, respectively). Both selection regimes and a control were replicated three times. Correlated responses to selection in females and in males were measured. A significant direct response to selection for time to remating was found in females from both selection regimes. Remating frequency of females showed a correlated response only in the females from the lines selected for faster time to remating. Time to first mating of virgin females showed no correlated response in either selection regime. No correlated response was found in males for time to remate, remating frequency or time to first mating of virgins, indicating that genetic correlations between the sexes do not influence the evolution of these traits in this population of D. melanogaster. There was no direct response to artificial selection for the ability of first males to deter females from remating. However, we found that the genotype of the first male to mate with a female could influence her time to remate; base stock males were better at deterring females from remating than were males from any of the selection lines. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed2001

Pure-phase selective excitation in fast-relaxing systems.

Selective pulses have been used frequently for small molecules. However, their application to proteins and other macromolecules has been limited. The long duration of shaped-selective pulses and the short T(2) relaxation times in proteins often prohibited the use of highly selective pulses especially on larger biomolecules. A very selective excitation can be obtained within a short time by using the selective excitation sequence presented in this paper. Instead of using a shaped low-intensity radiofrequency pulse, a cluster of hard 90 degrees pulses, delays of free precession, and pulsed field gradients can be used to selectively excite a narrow chemical shift range within a relatively short time. Thereby, off-resonance magnetization, which is allowed to evolve freely during the free precession intervals, is destroyed by the gradient pulses. Off-resonance excitation artifacts can be removed by random variation of the interpulse delays. This leads to an excitation profile with selectivity as well as phase and relaxation behavior superior to that of commonly used shaped-selective pulses. Since the evolution of scalar coupling is inherently suppressed during the double-selective excitation of two different scalar-coupled nuclei, the presented pulse cluster is especially suited for simultaneous highly selective excitation of N-H and C-H fragments. Experimental examples are demonstrated on hen egg white lysozyme (14 kD) and the bacterial antidote ParD (19 kD).

Magnetic Resonance Spectroscopy↗
PubMed1997

Ancestral Processes with Selection

In this paper, we show how to construct the genealogy of a sample of genes for a large class of models with selection and mutation. Each gene corresponds to a single locus at which there is no recombination. The genealogy of the sample is embedded in a graph which we call the ancestral selection graph. This graph contains all the information about the ancestry; it is the analogue of Kingman's coalescent process which arises in the case with no selection. The ancestral selection graph can be easily simulated and we outline an algorithm for simulating samples. The main goal is to analyze the ancestral selection graph and to compare it to Kingman's coalescent process. In the case of no mutation, we find that the distribution of the time to the most recent common ancestor does not depend on the selection coefficient and hence is the same as in the neutral case. When the mutation rate is positive, we give a procedure for computing the probability that two individuals in a sample are identical by descent and the Laplace transform of the time to the most recent common ancestor of a sample of two individuals; we evaluate the first two terms of their respective power series in terms of the selection coefficient. The probability of identity by descent depends on both the selection coefficient and the mutation rate and is different from the analogous expression in the neutral case. The Laplace transform does not have a linear correction term in the selection coefficient. We also provide a recursion formula that can be used to approximate the probability of a given sample by simulating backwards along the sample paths of the ancestral selection graph, a technique developed by Griffiths and Tavare (1994).

Journal Article↗
PubMed1996

Biochemical characterization of juvenile hormone esterases from lines selected for high or low enzyme activity in Gryllus assimilis.

In a previous study, activity of the insect endocrine regulator juvenile hormone esterase (JHE), in the cricket Gryllus assimilis, was subjected to bidirectional selection. This resulted in three pairs of high- and low-selected lines, each of which differed by 3.5-fold in JHE activity. In the present study, juvenile hormone esterases from these lines were characterized with respect to the Michaelis constant (K(m)), thermostability, and inhibition. None of three high-selected JHEs differed from its respective low-selected JHE in the Michaelis constant (K(m)) for juvenile hormone. Similarly, the high-selected JHEs did not differ from the low selected JHEs in thermostability or inhibition by either of two general esterase inhibitors (DFP, eserine) or a "JHE-specific" inhibitor (OTFP). Thus no evidence was obtained to suggest that the response to selection was due to allozymes or isozymes with altered kinetic or stability properties. Kinetic and stability properties were also very similar for the JHEs from the three high-selected or the three low-selected lines. Finally, none of the thermostability or inhibition profiles for any of the six JHEs exhibited sharp discontinuities, thus providing no evidence for the existence of multiple isozymes. The available evidence points to genetically variable regulators which affect the synthesis, degradation, or tissue distribution of JHE as being responsible for the divergence in JHE activity between the selected lines.

Acetone↗
PubMed1993

Space-based visual attention models and object selection: constraints, problems, and possible solutions.

One of the functions of visual attention is the selection of object information. This seems to be in line with an influential group of attentional models that assume that attentional selection is space based. These models assume that the selection of an object in vision is realized by selection of the location of that object. Whether this relatively simple idea of space-based attention and the corresponding, more elaborated space-based models are sufficient to handle selected constraints and problems of object selection is the main issue of this article. The first step toward an answer is to describe the common computational structure of space-based attentional models. Two model classes will be distinguished: capacity-limited models (e.g., Treisman, 1988; LaBerge & Brown, 1989) and models that do not assume a capacity limitation (e.g., Van der Heijden, 1992). Next, three kinds of task and data on object selection are introduced that are especially challenging for space-based models. The first type of data refers to experiments that require selection between overlapping objects. The second type of data concerns the influence of early perceptual grouping--a strong object-defining factor--on late response competition, and the third type consists of a selection task in which a high-level (semantic) attribute defines an object and controls selection. In all three cases, problems of space-based models are analyzed and possible solutions are sketched. Finally, a brief evaluative summary is given.

Attention↗
PubMed2000

In-vitro selection of Vitis vinifera 'Chardonnay' with Elsinoe ampelina culture filtrate is accompanied by fungal resistance and enhanced secretion of chitinase.

Proembryogenic masses of grapevine (Vitis vinifera L.) 'Chardonnay' (clone 02Ch) were exposed to the culture filtrate of Elsinoe ampelina (deBary) Shear, the causal agent of anthracnose disease. After four or five cycles of recurrent in-vitro selection with medium containing 40% fungal culture filtrate, putative resistant lines RC1 and RC2 respectively, were established. The selected lines inhibited the growth of E. ampelina and Fusarium oxysporium (Schlecht.) (isolated from watermelon) in a dual-culture assay and reduced the growth of mycelium on a conditioned-medium test, thus suggesting the involvement of extracellular compounds in resistance. Sodium dodecyl sulfate-polyacrylamide (SDS-PAGE) gel electrophoresis of extracellular proteins from spent suspension-culture medium showed enhanced secretion of new proteins by selected lines. A 36-kDa protein was immunodetected by a chitinase antiserum. This chitinase continued to express constitutively in differentiated somatic embryos and also in the intercellular fluids of plants regenerated from the selected lines. Somatic embryos from selected lines grew uninhibitedly in a medium containing 40% fungal culture filtrate, whereas non-selected (control) somatic embryos became necrotic and died within a few days. Plants regenerated from selected lines exhibited resistance to infection by E. ampelina in both greenhouse tests and detached leaf bioassays. Results suggest that embryogenic cells can be selected for resistance following in-vitro selection, resulting in resistant plants. Whether or not resistant cells pre-existed in the original embryogenic culture or were induced by the selection pressure could not be determined.

Ascomycota↗
PubMed1997

Charge and size selectivity of proteinuria in children with idiopathic nephrotic syndrome.

Experimental studies have pointed to charge selectivity as an important determinant of glomerular permeability to macromolecules. Loss of glomerular basement membrane (GBM) polyanion has been proposed as a cause of the selective proteinuria in minimal change nephrotic syndrome (MCNS). However, the presence of less-anionic albumin in urine than plasma from MCNS and focal and segmental glomerulosclerosis (FSGS) patients has been interpreted both as evidence for partial maintenance of charge selectivity and for involvement of other pathogenic mechanisms. The exact role of charge selectivity in the pathogenesis of nephrotic proteinuria remains controversial. We have examined the clearance of endogenous proteins of differing size and charge in children with idiopathic nephrotic syndrome (NS). Chromatofocusing was used to determine the isoelectric points (pIs) of albumins in paired plasma and urine samples from patients with FSGS (n = 6) and MCNS (n = 6). Charge selectivity was assessed by comparing the pIs of the fractions with the highest albumin concentration (model pI) in plasma and urine. The difference between the modal pIs was defined as the delta modal pI. Charge selectivity was also assessed from the albumin/transferrin and IgG4/IgG1 clearance ratios; size selectivity from the IgG1/albumin and IgG1/transferrin as well as the IgG4/albumin and IgG4/transferrin clearances. In children with FSGS, the mean (+/-SD) delta modal pI was -0.05 +/- 0.16, and in MCNS -0.05 +/- 0.11. Neither value differed significantly from zero. The albumin/transferrin clearance ratio showed no significant difference between FSGS and MCNS, but the IgG4/IgG1 clearance ratio was significantly higher in MCNS (P < 0.05). Size selectivity was significantly reduced in FSGS compared with MCNS (for IgG1/transferrin P < 0.01 and for IgG1/albumin P < 0.05). For IgG4/transferrin and IgG4/albumin, P was < 0.05. In conclusion, there was no evidence for residual charge selectivity in idiopathic NS associated with either MCNS or FSGS during nephrotic-range proteinuria. There was a significant loss of GBM size selectivity in children with FSGS with heavy proteinuria compared with children with MCNS with heavy proteinuria.

Adolescent↗
PubMed1981

Inversion of direction-selectivity to anterior fields in neurons of nucleus of the optic tract in rabbits with ocular albinism.

Extracellular recordings were made of 46 well-isolated single units in the nucleus of the optic tract (NOT) from 27 rabbits which were paralyzed but unanesthetized. Rabbits were selected from 3 varieties with ocular albinism. These units showed short latencies (mean = 2.2 msec, S.D. = 0.4) to chiasmic stimulation suggestive of monosynaptic innervation from retinal ganglion cells. Receptive fields were large and receptive field centers were confined to the projection of the visual streak. All units showed direction selectivity in which preferred stimulus motions were always nearly horizontal in the anterior or posterior direction. The direction selectivity of the units was broad in that excitatory acceptance angles were 180 degrees. Single units recorded from NOT in albino rabbits could be classified into 4 types based on regions of direction selectivity. The most common (64%) type of unit had receptive fields with two regions of opposed direction selectivity. The preferred direction of motion was anterior in lateral and posterior visual fields and was posterior in anterior visual fields. Two smaller groups of units (13% and 11%) had receptive fields with only one preferred direction. When the receptive field was anterior, the preferred direction was posterior. When the receptive field was lateral or posterior, the preferred direction was anterior. The least commonly encountered type of unit (7%) had receptive fields with two regions of direction selectivity. Anterior visual fields gave rise to anterior direction selectivity and lateral and posterior visual fields gave rise to posterior direction selectivity. The characteristics of NOT units are similar to those described for NOT units in pigmented rabbits except for an inversion of direction selectivity to stimulation from anterior visual fields. NOT units in albino rabbits show posterior direction selectivity when stimulation arises from anterior visual fields. The difference in directional preference in the visual receptive fields of the units in the NOT of albino rabbit may be responsible for the inversion of optokinetic pursuit eye movements characteristic of albino rabbits.

Albinism↗
PubMed1989

Rates of aminoacyl-tRNA selection at 29 sense codons in vivo.

We have placed aminoacyl-tRNA selection at individual codons in competition with a frameshift that is assumed to have a uniform rate. By assaying a reporter in the shifted frame, relative rates for association of the 29 YNN codons and their cognate aminoacyl-tRNAs were obtained during logarithmic growth in Escherichia coli. For five codons, three beginning with C and two with U, these relative rates agree with relative in vitro rates for elongation factor Tu-mediated aminoacyl-tRNA binding to ribosomes and subsequent GTP hydrolysis. Therefore, the frameshift assay probably measures this process in vivo. Observed rates for aminoacyl-tRNA selection span a 25-fold range. Therefore, the time required to transit different codons in vivo probably differs substantially. Codons very frequently used in highly expressed genes generally select aminoacyl-tRNAs more quickly than do rarely used codons. This suggests that speed of aminoacyl-tRNA selection is a significant factor determining biased use of synonymous codons. However, the preferential use of codons appears to be marked only for codons with the highest rates of aminoacyl-tRNA selection. Rapid selection in vivo is usually effected by elevation of the tRNA concentration for codons with moderate intrinsic speed (rate constant), not by choosing intrinsically fast codons. Despite a preference for high rate, there are quickly translated codons that are not commonly used, and common codons that are translated relatively slowly. Other factors are therefore more important than speed for some codons. Strong preference for rapid aminoacyl-tRNA selection is not observed in weakly expressed genes. Instead, there is a slight preference for slower aminoacyl-tRNA selection. The rate of aminoacyl-tRNA selection by a YNC codon is always greater than the rate of the corresponding YNU codon even though in many YNC/U pairs both codons react with the same elongation factor Tu/GTP/aminoacyl-tRNA complex. Thus, for these tRNAs, the differences between in vivo rate constants of tRNAs are dependent on the nature of anticodon base-pairing. However, no more general relationship is evident between codon/anticodon composition and rate of aminoacyl-tRNA selection. The frameshift method can be extended to all codons.

Base Sequence↗
PubMed1996

Daylength and body mass affect diet self-selection by Siberian hamsters.

Siberian hamsters exhibit a decrease in peak body mass/fat and caloric intake when they are exposed to short winter-like days (SDs) compared with hamsters exposed to long summer-like days (LDs). We hypothesize that the photoperiod may directly or indirectly mediate alterations in gustatory processing that may account for shifts in the preferences for specific food types and/or macronutrients. Two experiments lasting 14 days each were conducted to: 1) identify photoperiod-related differences in diet selection, and; 2) determine whether these differences were a primary effect of SD exposure or a secondary effect due to SD-induced decreases in body fat/mass. In Experiment 1, two groups of hamsters were exposed to either LDs or SDs and given access to three complex food types [sunflower seeds (SF); rabbit chow (RC); millet seeds (M)]. In addition to their photoperiod-induced decreased body and fat pad mass, and caloric intake, SD-housed hamsters exhibited significant differences in their patterns of diet selection and relative amounts of fat, carbohydrate (COH), and protein eaten compared with LD-housed hamsters. By the end of the experiment, SD-housed hamsters selected a diet higher in COH and protein and lower in fat than that selected by LD-housed hamsters. Because SD-housed hamsters decrease their body mass/fat, this may reflect an adaptive strategy to maintain a leaner body mass. A second experiment was conducted to test whether the diet selection pattern of SD-housed hamsters was due to the SD-induced decrease in body mass/fat. LD-housed hamsters were allowed to feed ad lib (AL group), or were food restricted (FR group) to simulate a SD-induced decrease in body mass. Both groups were then released into the diet self-selection paradigm. FR hamsters reversed their food restriction-induced decrease in body mass and showed concurrent alterations in diet self-selection patterns that were distinct from the SD-induced patterns seen in Experiment 1. Specifically, they showed a persistent hyperphagia and selected a larger proportion of their total calories as M (high COH) and less as SF (high fat) than did AL hamsters during their return to LD body mass levels. However, once LD body mass levels were achieved, they increased their SF intake, and thus fat consumption. Despite these dynamic daily changes, the average selection patterns of both the diet types and macronutrients were not different by the end of the experiment. Therefore, it appears that the SD-induced changes in the selection of food sources (and ultimately, the macronutrient composition of the diet) cannot be solely attributable to the SD-induced decreases in body mass.

Adipose Tissue↗
PubMed1994

Escherichia coli gpt as a positive and negative selectable marker in embryonal stem cells.

Transfection of HPRT- L fibroblasts with a plasmid containing two linked selectable markers genes, gpt and neo, regulated by the same eukaryotic control elements, yielded a 6-fold higher transfection frequency on selection for neo than for gpt. Transfection of HPRT- embryonal stem (ES) cells with the same plasmid yielded high levels of transfectants when selected for neo expression with G418, but a level of transfection greater than two orders of magnitude lower was observed when HAT supplemented medium was used to select for gpt expression. Selection for gpt expression in ES cells with medium containing mycophenolic acid and xanthine gave slightly higher frequencies of transfection, but still considerably lower than that for neo selection. In addition, mycophenolic acid exhibited a general cytotoxicity to ES cells with the window between toxicity of this compound to gpt- ES cells and gpt+ ES cells being very narrow. Cells selected with mycophenolic acid and xanthine for expression of gpt remained sensitive to HAT selection. Expression of gpt in a representative ES cell line, selected on mycophenolic acid and xanthine, was verified by Northern analysis and sensitivity to 6-thioguanine. While the level of mRNA expression in this ES cell line was insufficient to support growth via purine salvage when exposed to HAT medium, identical levels of gpt expression in HPRT- L cells, as judged by Northern analysis, allowed for normal growth in HAT medium. This suggests that ES cells place a greater demand on purine nucleotide biosynthesis than L cells. These results are discussed in terms of the use of gpt as a positive and negative selectable marker for gene targeting via homologous recombination in ES cells.

Cell Line↗
PubMedDate not supplied

The selection effects of the inclusion of a chiropractic benefit on the patient population of a managed health care organization.

OBJECTIVE: The aim of this study is to measure the selection effects of the inclusion of a chiropractic benefit on a managed care health plan. DESIGN: An analysis of enrollment data from a managed care health plan over a 4-year period was conducted. Employers could select the managed care plan with or without a chiropractic care benefit. Comparisons of demographic and comorbid characteristics were made between employees who had the chiropractic benefit and those who did not, and between individuals who self-selected chiropractic care and those who self-selected medical care. RESULTS: The cohort with chiropractic coverage was younger with fewer subjects in the older age group (>65 years; 6.5% vs 9.6%) and more subjects in the younger age group (0-17 years; 31.9% vs 26.2%). The mean age of the group with coverage was 32.9 compared with 35.5 in the group without coverage. Comparing self-selected chiropractic patients to self-selected medical patients, there were fewer subjects older than 65 years in the chiropractic group (4.9% vs 9.2%) and fewer subjects aged 0 to 17 years (9.4% vs 19.4%). In 6 of the 8 comorbid conditions studied, the rates were lower in the cohort with chiropractic coverage compared with the group without coverage. The rates of comorbid conditions in self-selected chiropractic patients were lower in all 8 categories compared with self-selected medical patients. CONCLUSION: The inclusion of a chiropractic benefit in a health plan produces a modest favorable selection processes resulting in a slightly younger patient population with fewer comorbidities. At the level of patient self-selection, chiropractic patients are considerably younger and healthier than comparable medical patients.

Adolescent↗
PubMed2005

A band-selective composite gradient: application to DQF-COSY.

We describe a unique band-selective method that utilizes a selective composite gradient to simultaneously achieve band selection and coherence pathway selection. This element is similar to the composite gradient known as the CLUB sandwich except the original broadband pulses have been replaced with selective pulses and the strengths of the antipolar gradients have been unbalanced. In this way, only the signals within the inversion band will continue to dephase throughout the duration of the element and satisfy the proper encoding-to-decoding gradient ratio necessary for coherence selection. Apart from the inverted polarity and asymmetry of the gradients, the band-selective CLUB sandwich is identical to the DPFGSE sequence and provides many of its desirable characteristics. We have successfully incorporated the band-selective CLUB into the DQF-COSY pulse sequence to create a band-selective experiment that offers the selectivity desired for resolution enhancement while maintaining excellent phase behavior. This is demonstrated on the congested aliphatic region of the ionophorous antibiotic Lasalocid A.

Algorithms↗
PubMed2005

Optimal temperature for selective cerebral perfusion.

OBJECTIVE: Although combinations of hypothermic circulatory arrest and antegrade selective cerebral perfusion are used for cerebral protection during arch surgery, there is no consensus regarding the optimal temperature during selective cerebral perfusion. This study explored the effect of different temperatures during selective cerebral perfusion on cerebral metabolism and neurologic outcome. METHODS: In this blinded study, 40 pigs (19-21 kg) were randomized into 4 groups after 30 minutes of hypothermic circulatory arrest at 20 degrees C. During a 60-minute interval of selective cerebral perfusion, with flow regulated to maintain a perfusion pressure of 50 mm Hg, pigs were perfused at 10 degrees C, 15 degrees C, 20 degrees C, and 25 degrees C. Fluorescent microspheres enabled calculation of cerebral blood flow during perfusion and recovery. Hemodynamics, intracranial pressure, cerebrovascular resistance, and oxygen consumption were also monitored. Behavioral scores were obtained for 7 days after surgery. RESULTS: Cerebral blood flow decreased significantly ( P < .002) during cooling in all groups: it was significantly higher throughout selective cerebral perfusion in the 20 degrees C to 25 degrees C versus the 10 degrees C to 15 degrees C group ( P = .0001) and remained higher during recovery ( P = .0001). Oxygen consumption decreased significantly with cooling ( P = .0001), remained low during perfusion, and rebounded with rewarming but was significantly lower at 10 degrees C to 15 degrees C than at 20 degrees C to 25 degrees C throughout selective cerebral perfusion ( P = .003) and after CPB was discontinued ( P = .001). Postoperative behavioral scores were significantly better after selective cerebral perfusion at 10 degrees C to 15 degrees C than at 20 degrees C to 25 degrees C ( P = .001). CONCLUSIONS: This study suggests that selective cerebral perfusion at 10 degrees C to 15 degrees C provides better cerebral protection than selective cerebral perfusion at 20 degrees C to 25 degrees C, even though oxygen consumption remains low for hours after selective cerebral perfusion at 10 degrees C to 15 degrees C. Prompt return of metabolism to baseline levels after hypothermic circulatory arrest/selective cerebral perfusion does not necessarily predict superior behavioral outcome.

Animals↗
PubMed2005

Normal and abnormal face selectivity of the M170 response in developmental prosopagnosics.

Developmental prosopagnosia is a lifelong impairment in face recognition despite normal low-level visual processing. Here we used magnetoencephalography (MEG) to examine the M170 response, a component occurring approximately 170 ms after stimulus onset, in a group of five developmental prosopagnosics. In normal subjects, the M170 is "face-selective", with a consistently higher amplitude to faces than to a wide variety of other visual stimulus categories; the N170, a component recorded using event-related potentials (ERP) and thought to be analogous to the M170, also shows this "face selectivity". Two previous ERP studies with developmental prosopagnosics have found attenuation or absence of face selectivity in the N170 response of these subjects [Bentin, S., Deouell, L. Y., and Soroker, N. (1999). Selective visual streaming in face recognition: Evidence from developmental prosopagnosia. Neuroreport, 10, 823-827; Kress, T., and Daum, I. (2003). Event-related potentials reflect impaired face recognition in patients with congenital prosopagnosia. Neuroscience Letters, 352, 133-136]. Three of our developmental prosopagnosic group showed this non-selective pattern at the M170 while the remaining two prosopagnosics were indistinguishable from normal controls. Thus, impaired face recognition is not necessarily correlated with an absence of the "face-selective" M170. Furthermore, ERP recordings collected simultaneously in the two developmental prosopagnosics with seemingly selective M170s also showed N170s within the same normal selective range, demonstrating that the face-selective signals found with MEG are not due to differences between MEG and ERP. While the presence of face selectivity at these neurophysiological markers is insufficient for predicting normal behavioral performance with faces, it could help to distinguish different classes of face recognition deficits.

Adult↗
PubMed2006

Influence of nutrient preload on encapsulated macronutrient selection in European sea bass.

The sea bass is a teleost that is able to regulate its energy intake by selecting from pure macronutrient sources, although the regulatory mechanisms involved in this selection are unknown. Nutrient preloads are known to reduce food intake and modify macronutrient selection patterns in mammals, but no information is available on its effects in fish. The aim of the present work was to determine the effect of orally administered macronutrient preloads of protein (P), fat (F) or carbohydrate (CH) on the subsequent macronutrient selection, using for the purpose feed consisting of CH, P or F packaged separately in gelatin capsules. The macronutrient preloads left the total food intake unaltered, but caused differential changes in the pattern of macronutrient selection. The CH preload increased the selection of CH (39%) and decreased that of P (20%), independently of the fish's previous nutritional preferences. The F preload induced an F increase (32%) and a P decrease (18%) in P-preferring fish, but not in F-preferring fish in which the macronutrient selection pattern remained unaffected. The P preload stimulated F selection by 42% in P-preferring fish, but left the macronutrient selection pattern unchanged in F-preferring fish. In conclusion, oral macronutrient preloads affected the pattern of macronutrient selection in fish, acting by post-ingestive mechanisms. The effect was influenced by the fish's previous nutritional preference and/or status, which could depend on its metabolic capacity.

Administration, Oral↗
PubMed2000

Molecular determinants of anion selectivity in the cystic fibrosis transmembrane conductance regulator chloride channel pore.

Ionic selectivity in many cation channels is achieved over a short region of the pore known as the selectivity filter, the molecular determinants of which have been identified in Ca(2+), Na(+), and K(+) channels. However, a filter controlling selectivity among different anions has not previously been identified in any Cl(-) channel. In fact, because Cl(-) channels are only weakly selective among small anions, and because their selectivity has proved so resistant to site-directed mutagenesis, the very existence of a discrete anion selectivity filter has been called into question. Here we show that mutation of a putative pore-lining phenylalanine residue, F337, in the sixth membrane-spanning region of the cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel, dramatically alters the relative permeabilities of different anions in the channel. Specifically, mutations that reduce the size of the amino acid side chain present at this position virtually abolish the relationship between anion permeability and hydration energy, a relationship that characterizes the anion selectivity not only of wild-type CFTR, but of most classes of Cl(-) channels. These results suggest that the pore of CFTR may indeed contain a specialized region, analogous to the selectivity filter of cation channels, at which discrimination between different permeant anions takes place. Because F337 is adjacent to another amino acid residue, T338, which also affects anion selectivity in CFTR, we suggest that selectivity is predominantly determined over a physically discrete region of the pore located near these important residues.

Amino Acid Substitution↗
PubMed1982

Neutral carrier Na+- and Ca2+-selective microelectrodes for intracellular application.

Na+- and Ca2+-selective microelectrodes were made with Simon's neutral carrier ETH 227 and ETH 1001, respectively, and their properties were studied for intracellular application. The kNaK (selectivity coefficient for Na+ with respect to K+) values of the Na+-selective microelectrodes were in the range of 0.01-0.02, which is comparable to those of recessed-tip Na+-selective glass microelectrodes. The kNaMg values of the microelectrodes were approximately 0.005 so that the interference by intracellular Mg2+ levels could be negligible. The kNaCa values were approximately 2 and the Na+-selective microelectrodes were more selective to Ca2+ than Na+. This indicates that their intracellular application requires special care to handle Ca2+ interference under certain conditions. The kNaK, kNaMg, and kNaCa values did not depend significantly on the methods used for their determination or on the ion activity levels tested. The Nicolsky equation described well the microelectrode potentials in the mixed solutions of NaCl (1-100 mM) and KCl. Potential and resistance of the microelectrodes were stable for a long period and their response time was fast. The results indicate that the Na+-selective microlectrodes are suitable for measurements of intracellular Na ion activities. Ca2+-selective microelectrode potentials at Ca2+ concentrations lower than 10(-4) M changed significantly for the first 2-3 h and then became fairly stable. The rate of the potential change was dependent on the column length of the Ca2+-selective liquid filled. Potentials of the microelectrodes varied from 10-20 mV for Ca2+ between 10(-7) and 10(-6) M concentrations, which may be the cytosolic free-Ca2+ range. With the Ca2+ concentrations greater than 10(-6) M, the microelectrodes had potential changes of approximately 30 mV or greater for a tenfold change in Ca2+ concentration. The kCaK and kCaNa values were in the ranges of 10(-5)-10(-6) and 10(-4)-10(-5), respectively. The kCaMg values were approximately 10(-7). The results show that the Ca2+-selective microelectrodes can be used for measurements of cytosolic Ca ion activities.

Calcium↗