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PubMed1989

Mechanisms of short-term saccadic adaptation.

A number of processes have been identified that adaptively modify oculomotor control components. The adaptive process studied here can be reliably produced over a short period of time by a visual stimulus that forces postsaccadic error. This short-term adaptive process, usually termed parametric adaptation, consists of a change in response amplitude that develops progressively over 50 to 100 training stimuli. The resulting compensation is proportional to, but substantially less than, the error induced by the training stimuli. Both increases and decreases in response amplitude can be evoked by an appropriately timed and directed movement of the stimulus target, which forces postsaccadic error. Results show that a single type of training stimulus can influence movements over a broad spatial region, provided these movements are in the same direction as the training stimulus. Experiments that map the range of modification suggest that the increasing adaptive modification operates by remapping final position, whereas the decreasing adaptive modification is achieved through an overall reduction of gain. Training stimuli that attempt to evoke both increases and decreases in the same region show a net modification equivalent to the algebraic addition of individual adaptive processes.

Adolescent↗
PubMed1980

A further parallel between selective adaptation and contrast.

It is generally believed that selective adaptation effects in speech perception are due to a reduction in sensitivity of auditory feature detectors. Recent evidence suggest that these effects may derive instead from contrast. In a further test of the contrast hypothesis, we conducted two experiments each involving both adaptation and contrast sessions with matching stimulus sets. During the adaptation sessions of Experiment 1, subjects identified two series of velar stimuli varying in voice onset time, [ga]-[kha] and [gi]-[khi], before and after adaptation with of the following stimuli: [ga], [kha], [gi], and [khi]. In the contrast session, subjects identified either of two ambiguous test items (drawn from near the phonetic boundaries of the [ga]-[kha] and the [gi]-[khi] series) following a single presentation of [ga], [kha], [gi], or [khi]. For both the adaptation and contrast sessions, (a) the [--a] test items were more greatly affected (in a contrast direction) by the [--a] than by the [--i] adaptor/context stimuli, and (b) the [--i] test items were not differentially affected by the [--1] and [--i] adaptor/context stimuli. An analogous design was used in Experiment 2, except that the stimulus sets varied in pitch rather than vowel quality. For both the adaptation and contrast sessions, the test items were not differentially affected by the pitch of the adaptor/context stimulus. These parallel results provide further evidence that adaptation effects are actually a form of contrast.

Habituation, Psychophysiologic↗
PubMed2003

Adaptive intrapatient dose escalation of cisplatin in combination with low-dose vp16 in patients with nonsmall cell lung cancer.

The objective of this phase II and pharmacologic study was to explore the feasibility, toxicity and activity of adaptive intrapatient dose escalation of cisplatin in a dose-intensive weekly schedule using predefined levels of exposure, with the ultimate aim to improve the antitumour activity of the therapy in patients with nonsmall cell lung cancer (NSCLC). Platinum DNA-adduct levels in peripheral white blood cells during treatment were used as the primary parameter for adaptive dosing. If DNA-adduct levels were not available, the area under the concentration-time curve (AUC) of unbound platinum in plasma was used for dose adaptation. Target levels for DNA-adducts and AUC have been defined in a previously performed pharmacologic study. The feasibility of adaptive dosing was tested in 76 patients with stage IIIB and IV NSCLC, who were planned to receive 6 weekly courses of cisplatin at a starting dose of 70 mg m(-2), together with daily low oral dose of 50 mg VP16. In total, 37 patients (49%) who were given more than one course received a dose increase varying from 10 to 55%. The majority of patients reached the defined target levels by a dose increase during course two. Relevant grade 2 neurotoxicity was observed in eight (10%) patients and reversible ototoxicity grade 2 in 14 (18%) patients. The strategy of adaptive intrapatient dose adjustment of cisplatin is practically feasible in a research setting even when results for dose adaptation have to be reported within a short time-period of 1 week. The toxicity appeared to be manageable in this cohort of patients. In some patients, exposure after the standard dose was substantially lower than the defined target level and significant dose escalations of more than 50% had to be applied. The response rate (RR) was relatively high: overall 40% (29 out of 72 patients) partial remission (PR), in patients with stage IIIB the RR was 60% (15 out of 25 patients) and with stage IV 30% (14 out of 47 patients). Randomised studies are needed to determine whether the adaptive dosing strategy results in better efficacy than standard dosing.

Administration, Oral↗
PubMed1989

Urinary kallikrein excretion during potassium chloride infusion in potassium-adapted rats: effect of amiloride.

1. Urinary kallikrein excretion in the anaesthetized rat was measured during intravenous KCl infusion in control and in K+-adapted rats. 2. The infusion of 0.1 mol/l KCl at 3.0 ml/h for 60 min in control rats resulted in a significant increase in urinary kallikrein excretion, associated with diuresis, natriuresis and kaliuresis. 3. When rats were offered 0.1 mol/l KCl to drink ad libitum for 14 days (K+-adaptation), the basal excretion of kallikrein was higher than in the control rats. In K+-adapted rats, intravenous infusion of 0.1 mol/l KCl resulted in significantly greater increase in urinary kallikrein excretion than in the control rats. 4. The Na+-channel blocker, amiloride (8.5 mg/kg body weight), significantly increased urinary kallikrein excretion immediately after injection in control and K+-adapted rats. However, in the subsequent 60 min, kallikrein excretion decreased markedly to values lower than those before injection of amiloride. 5. When amiloride was superimposed on a continuous 0.1 mol/l KCl infusion in K+-adapted rats, there was an immediate increase in kallikrein excretion. In the subsequent 20 min, kallikrein excretion decreased only to increase again in the next 40 min of KCl infusion. 6. Since amiloride injection reduces urinary kallikrein excretion in control and K+-adapted rats, the results suggest that urinary kallikrein excretion in the rat is through a mechanism(s) affected by amiloride. The high urinary kallikrein excretion and the greater response to KCl infusion in K+-adapted rats suggest that the K+-transport mechanism is more important than the mechanism affected by amiloride.

Amiloride↗
PubMed2006

Epidermal growth factor receptor signaling regulates Bax and Bcl-w expression and apoptotic responses during intestinal adaptation in mice.

BACKGROUND & AIMS: Normal intestinal adaptation to massive small-bowel resection requires intact epidermal growth factor receptor signaling and consists of increased enterocyte proliferation and apoptosis. Although emphasis has been placed on understanding the regulation of proliferation, few studies have evaluated the mechanism and contribution of apoptosis to the adaptation response. We sought to test the hypothesis that epidermal growth factor receptor signaling regulates specific Bcl-2 family members (Bax and Bcl-w) to direct apoptosis and adaptation after massive small-bowel resection. METHODS: Laser capture microdissection microscopy permitted measurement of Bax and Bcl-w messenger RNA expression in crypt and villus enterocytes in control conditions and under epidermal growth factor receptor-inhibited (waved-2 mice) or stimulated (epidermal growth factor transgenic mice) conditions after a 50% small-bowel resection or sham operation. Resection-induced adaptation was then studied in Bax-null and Bcl-w-null mice under control circumstances and after epidermal growth factor receptor stimulation. RESULTS: When compared with Bcl-w, the most significant expression changes were observed with Bax and took place within crypt enterocytes. Epidermal growth factor receptor stimulation resulted in a decreased ratio of Bax to Bcl-w expression and decreased rates of apoptosis. Bax-null mice had no apoptosis response to small-bowel resection and displayed an amplified adaptation response to the administration of epidermal growth factor. Bcl-w-null mice had poor survival and impaired adaptation to small-bowel resection, an effect that was rescued by crossbreeding these mice with epidermal growth factor transgenic mice. CONCLUSIONS: The crypt expression of Bax and Bcl-w is influenced by epidermal growth factor receptor signaling and is key for the regulation of apoptosis. Epidermal growth factor receptor stimulation, coupled with apoptosis inhibition, may provide a novel strategy to amplify adaptation responses in patients after massive intestinal loss.

Animals↗
PubMed1994

Dichoptically viewed colour aftereffects produced by monocular adaptation.

Colour aftereffects were observed in dichoptically viewed achromatic striped patterns after a 25 s period of monocular adaptation to an homogeneous coloured field of red, green, or blue. Three test conditions of dichoptic viewing were used. In condition 1, black line patterns were viewed dichoptically on fused white backgrounds. Stimuli used in condition 2 were similar except that they were white line patterns on black backgrounds. Last, condition 3 was realised with the same stimulus patterns utilised in condition 1, except that the mode of dichoptic viewing produced a juxtaposition rather than a fusion of the two white backgrounds containing the line patterns. Some colour aftereffect was obtained for each colour-adaptation condition and in each test condition. It consisted in a negative colour aftereffect (NCA) in the adapted eye (the colour seen was roughly the complementary of the adaptation colour) and/or a positive colour aftereffect (PCA) in the unadapted eye (the colour seen tended rather to be similar in hue to the adaptation colour). In fact, the following four kinds of responses were obtained: (i) two colour aftereffects, one seen by each eye, ie a NCA involving the adapted eye and a PCA involving the unadapted eye; (ii) a NCA involving the adapted eye only; (iii) a PCA involving the unadapted eye only; (iv) no colour aftereffect at all. Results obtained in different test conditions permitted us to assert that both kinds of colour aftereffect could be produced with white patterns on dark backgrounds as well as with black patterns on white backgrounds and did not require binocular fusion of the white backgrounds.(ABSTRACT TRUNCATED AT 250 WORDS)

Color Perception↗
PubMed1996

Re-evaluation of local adaptation for motion aftereffect.

A motion aftereffect (MAE) can be induced by stimuli moving in surrounding areas. This suggests the relevance of mechanisms for relative motion, rather than early-level motion detectors, which are considered to work locally. Experiments are reported in which the role of local adaptation in the MAE with a stimulus configuration comprising relative motion has been discussed. Sinusoidal gratings were presented in three rectangular windows: a centre window, and two windows one above and one below the central one. The surrounding top and bottom windows, which were divided into left and right halves, had gratings presented in only one of the two halves. The MAE duration was measured after adaptation to motion either in the central or in the surrounding windows, by controlling the regions with the gratings. From this, the regions of surrounding gratings were found not to have a significant effect with adaptation in the centre window. With adaptation in the surrounds, however, these regions did affect the MAE; the MAE duration was reduced when the adapted region had no gratings in the test phase. Thus, for an MAE it is necessary for the adapted area to be covered with stimuli in the test phase, which indicates the dominance of local adaptation for the MAE even when relative motion is relevant in producing the MAE.

Adult↗
PubMed2001

Monaural loudness adaptation for middle-intensity middle-frequency signals: the importance of measurement technique.

Using the Simple Adaptation technique (SA) and the Ipsilateral Comparison Paradigm (ICP), the authors studied monaural loudness adaptation to a middle-intensity [60 dB(A)] tone at signal frequencies of 250, 1000, and 4000 Hz in the left and right ears. Adaptation effects were absent when the SA procedure was used. However, they were observed uniformly across all frequency values with the ICP, a result that challenges the assertion in the literature, on the basis of SA measures, that loudness adaptation for middle-intensity signals occurs only at frequencies above 4000 Hz. The ICP features periodic intensity modulations (+/-10 dB relative to the base signal) to accommodate listeners' needs for referents by which they can gauge subtle changes in the loudness of the adapting tone, a key component that is missing in the SA method. Adaptation effects in this investigation were similar in both ears, supporting the equal susceptibility assumption common in loudness adaptation studies.

Adolescent↗
PubMed1992

Effects of Pointing Rate and Availability of Visual Feedback on Visual and Proprioceptive Components of Prism Adaptation.

While looking through laterally displacing prisms, subjects pointed 60 times straight ahead of their nose at a rate of one complete movement every 2 or 3 s, with visual feedback available early in the pointing movement or delayed until the end of the movement. Sagittal pointing was paced such that movement speed covaried with pointing rate. Aftereffect measures (obtained after every 10 pointing trials) showed that when the limb became visible early in a pointing movement, proprioceptive adaptation was greater than visual, but when visual feedback was delayed until the end of the movement, the reverse was true. This effect occurred only with the 3-s pointing rate, however. With the 2-s pointing rate, adaptation was predominately proprioceptive in nature, regardless of feedback availability. Independent of the availability of visual feedback, visual adaptation developed more quickly with 3-s pointing, whereas proprioceptive adaptation developed more rapidly with 2-s pointing. These results are discussed in terms of a model of perceptual-motor organization in which the direction of coordinative (guidance) linkage between eye-head (visual) and hand-head (proprioceptive) systems (and consequently the locus of discordance registration and adaptive recalibration) is determined jointly by pointing rate and feedback availability. An additional effect of pointing rate is to determine the rate of discordant inputs. Maximal adaptive recalibration occurs when the input (pointing) rate matches the time constant of the adaptive encoder in the guided system.

Journal Article↗
PubMed2005

Microswitch clusters to enhance adaptive responses and head control: a programme extension for three children with multiple disabilities.

PURPOSE: We assessed the possibility of extending adaptive responding and head control in three children with multiple disabilities through the use of microswitch clusters. METHOD: The children had previously learned to perform an adaptive hand response and to control head position during that response. They were now taught one or two new adaptive responses (foot lifting, leg touching, or vocalization) and to combine such responses with appropriate head position. Microswitch clusters served to ensure that an adaptive response was followed by positive stimulation only if it was combined with appropriate head position. RESULTS: The results were positive with the children learning the new adaptive responses and combining them with appropriate head position. This performance was maintained during two- or three-month post-intervention checks. During these checks, the children were also successful in using the old adaptive hand response with appropriate head position. CONCLUSIONS: The use of microswitch clusters was effective to extend the level of adaptive responding and enhance appropriate head position during this responding. This outcome, which indicates a successful technical replication and procedural extension of previous work in the area, has positive practical implications for educational and occupational programmes for children with multiple disabilities.

Child↗
PubMed2001

Evidence that both ligand binding and covalent adaptation drive a two-state equilibrium in the aspartate receptor signaling complex.

The transmembrane aspartate receptor of bacterial chemotaxis regulates an associated kinase protein in response to both attractant binding to the receptor periplasmic domain and covalent modification of four adaptation sites on the receptor cytoplasmic domain. The existence of at least 16 covalent modification states raises the question of how many stable signaling conformations exist. In the simplest case, the receptor could have just two stable conformations ("on" and "off") yielding the two-state behavior of a toggle-switch. Alternatively, covalent modification could incrementally shift the receptor between many more than two stable conformations, thereby allowing the receptor to function as a rheostatic switch. An important distinction between these models is that the observed functional parameters of a toggle-switch receptor could strongly covary as covalent modification shifts the equilibrium between the on- and off-states, due to population-weighted averaging of the intrinsic on- and off-state parameters. By contrast, covalent modification of a rheostatic receptor would create new conformational states with completely independent parameters. To resolve the toggle-switch and rheostat models, the present study has generated all 16 homogeneous covalent modification states of the receptor adaptation sites, and has compared their effects on the attractant affinity and kinase activity of the reconstituted receptor-kinase signaling complex. This approach reveals that receptor covalent modification modulates both attractant affinity and kinase activity up to 100-fold, respectively. The regulatory effects of individual adaptation sites are not perfectly additive, indicating synergistic interactions between sites. The three adaptation sites at positions 295, 302, and 309 are more important than the site at position 491 in regulating attractant affinity and kinase activity, thereby explaining the previously observed dominance of the former three sites in in vivo studies. The most notable finding is that covalent modification of the adaptation sites alters the receptor attractant affinity and the receptor-regulated kinase activity in a highly correlated fashion, strongly supporting the toggle-switch model. Similarly, certain mutations that drive the receptor into the kinase activating state are found to have correlated effects on attractant affinity. Together these results provide strong evidence that chemotaxis receptors possess just two stable signaling conformations and that the equilibrium between these pure on- and off-states is modulated by both attractant binding and covalent adaptation. It follows that the attractant and adaptation signals drive the same conformational change between the two settings of a toggle. An approach that quantifies the fractional occupancy of the on- and off-states is illustrated.

Binding Sites↗
PubMed2006

Fast adaptation in mouse olfactory sensory neurons does not require the activity of phosphodiesterase.

Vertebrate olfactory sensory neurons rapidly adapt to repetitive odorant stimuli. Previous studies have shown that the principal molecular mechanisms for odorant adaptation take place after the odorant-induced production of cAMP, and that one important mechanism is the negative feedback modulation by Ca2+-calmodulin (Ca2+-CaM) of the cyclic nucleotide-gated (CNG) channel. However, the physiological role of the Ca2+-dependent activity of phosphodiesterase (PDE) in adaptation has not been investigated yet. We used the whole-cell voltage-clamp technique to record currents in mouse olfactory sensory neurons elicited by photorelease of 8-Br-cAMP, an analogue of cAMP commonly used as a hydrolysis-resistant compound and known to be a potent agonist of the olfactory CNG channel. We measured currents in response to repetitive photoreleases of cAMP or of 8-Br-cAMP and we observed similar adaptation in response to the second stimulus. Control experiments were conducted in the presence of the PDE inhibitor IBMX, confirming that an increase in PDE activity was not involved in the response decrease. Since the total current activated by 8-Br-cAMP, as well as that physiologically induced by odorants, is composed not only of current carried by Na+ and Ca2+ through CNG channels, but also by a Ca2+-activated Cl- current, we performed control experiments in which the reversal potential of Cl- was set, by ion substitution, at the same value of the holding potential, -50 mV. Adaptation was measured also in these conditions of diminished Ca2+-activated Cl- current. Furthermore, by producing repetitive increases of ciliary's Ca2+ with flash photolysis of caged Ca2+, we showed that Ca2+-activated Cl- channels do not adapt and that there is no Cl- depletion in the cilia. All together, these results indicate that the activity of ciliary PDE is not required for fast adaptation to repetitive stimuli in mouse olfactory sensory neurons.

1-Methyl-3-isobutylxanthine↗
PubMed2002

The effectiveness of local adaptation of nationally produced clinical practice guidelines.

BACKGROUND: Local adaptation is often reported in the literature to be an important strategy in achieving local ownership and relevance of guidelines in order to increase the likelihood of their uptake and implementation. However, the process is also potentially time-consuming and costly. OBJECTIVE: The aim of this study was to determine the impact of local adaptation of nationally produced clinical practice guidelines (CPGs) on the knowledge, attitude and reported practices of GPs. METHODS: Two Divisions of General Practice in Adelaide, Australia were selected and randomized to adapt a nationally produced CPG (on Stroke Prevention) by the National Health and Medical Research Council or use the original version. The order of the interventions was reversed for a second guideline (on management of Lower Urinary Tract Symptoms in Men). An identical multifaceted dissemination strategy was adopted for both sets of guidelines in the two divisions. Prior to the intervention, a random sample of 200 GPs from each Division was sent a postal survey about their knowledge, attitudes and reported practices. This was repeated 3 months after the dissemination phase. RESULTS: Sixty-one per cent (243/400) of the GPs responded to the initial survey and, of these, 76% (184/243) responded to the follow-up survey. Overall, awareness of both sets of guidelines was significantly increased. For stroke, 38% of respondents across both Divisions reported that their practice had changed as a result of the guidelines. For management of lower urinary tract symptoms in men, the corresponding proportion was 52%. Agreement with specific recommendations from both guidelines was also increased following their dissemination. However, these changes were independent of whether or not the guidelines had been locally adapted. The local adaptation process involved no substantive change in content and was estimated to cost AUD$5600 (per Division) independent of the costs of the dissemination process. CONCLUSIONS: Whilst this study found significant changes in knowledge, attitude and reported practice as a result of disseminating guidelines, it did not find any additional effect from the local adaptation process itself. This suggests that the emphasis and investment in promoting guideline implementation should be placed on multifaceted dissemination strategies rather than local adaptation per se.

Attitude of Health Personnel↗
PubMed1996

Anti-CD38 prevents the development of the adaptive response induced by X-rays in human lymphocytes.

Irradiation of human lymphocytes (1 cGy X-rays, 37 degrees C) evoked an approximately 30% decrease in the frequency of micronuclei upon subsequent X-irradiation (1.5 Gy). The response was reflected in a lower micronucleus frequency but not in the DNA repair rate measured by the comet assay directly after the challenge dose. Treatment of lymphocytes with anti-CD38 antibody 1 h before irradiation with the adaptive dose prevented the development of the adaptive response measured as micronuclei frequency, but adaptation was not reflected in a lower rate of DNA repair, measured by the alkaline version of the 'comet' assay. In lymphocytes that were anti-CD38-treated and irradiated and or irradiated with the adaptive dose the rate of DNA repair was not changed. However, the mean DNA damage level in adapted anti-CD38-treated lymphocytes was significantly lower than that in the control lymphocytes at all time points. We conclude that ligation of CD38 by antibody initiates signalling that prevents the development of the adaptive response induced by X-rays. Lower chromosome damage revealed by the cytokinesis block-micronucleus test in the adapted lymphocytes is unrelated to DNA repair rate.

ADP-ribosyl Cyclase↗
PubMed2005

JCat: a novel tool to adapt codon usage of a target gene to its potential expression host.

A novel method for the adaptation of target gene codon usage to most sequenced prokaryotes and selected eukaryotic gene expression hosts was developed to improve heterologous protein production. In contrast to existing tools, JCat (Java Codon Adaptation Tool) does not require the manual definition of highly expressed genes and is, therefore, a very rapid and easy method. Further options of JCat for codon adaptation include the avoidance of unwanted cleavage sites for restriction enzymes and Rho-independent transcription terminators. The output of JCat is both graphically and as Codon Adaptation Index (CAI) values given for the pasted sequence and the newly adapted sequence. Additionally, a list of genes in FASTA-format can be uploaded to calculate CAI values. In one example, all genes of the genome of Caenorhabditis elegans were adapted to Escherichia coli codon usage and further optimized to avoid commonly used restriction sites. In a second example, the Pseudomonas aeruginosa exbD gene codon usage was adapted to E.coli codon usage with parallel avoidance of the same restriction sites. For both, the degree of introduced changes was documented and evaluated. JCat is integrated into the PRODORIC database that hosts all required information on the various organisms to fulfill the requested calculations. JCat is freely accessible at http://www.prodoric.de/JCat.

Algorithms↗
PubMed2004

Dominant negative effect of wild-type NS5A on NS5A-adapted subgenomic hepatitis C virus RNA replicon.

An efficient model is currently used to study hepatitis C virus (HCV) replication in cell culture. It involves transfection in Huh7, a hepatoma-derived cell line, of an antibiotic (neomycin) selectable HCV subgenomic replicon encoding the non-structural (NS) proteins from NS3 to NS5B. However, strong and sustained replication is achieved only on the appearance of adaptive mutations in viral proteins. The most effective of these adaptive mutations are concentrated mainly in NS5A, not only into the original Con1 but also in the recently established HCV-BK and HCV-H77 isolate-derived replicons. This suggests that the expression of wild-type (wt) NS5A may not allow efficient HCV RNA replication in cell culture. With the use of a beta-lactamase reporter gene as a marker for HCV replication and TaqMan RNA analysis, the replication of different HCV replicons in cotransfection experiments was investigated. Comparing wt with NS5A-adapted replicons, the strong evidence accumulated showed that the expression of wt NS5A was actually able to inhibit the replication of NS5A-adapted replicons. This feature was characterized as a dominant negative effect. Interestingly, an NS5B (R2884G)-adapted replicon, containing a wt NS5A, was dominant negative on an NS5A-adapted replicon but was not inhibited by the original Con1 replicon. In conclusion, these studies revealed that the original wt Con1 replicon is not only incompetent for replication in cell culture, but is also able to interfere with NS5A-adapted replicons.

Amino Acid Substitution↗
PubMed1985

Adaptation of Tobacco Cells to NaCl.

Cell lines of tobacco (Nicotiana tabacum L. var Wisconsin 38) were obtained which are adapted to grow in media with varying concentrations of NaCl, up to 35 grams per liter (599 millimolar). Salt-adapted cells exhibited enhanced abilities to gain both fresh and dry weight in the presence of NaCl compared to cells which were growing in medium without NaCl (unadapted cells). Tolerance of unadapted cells and cells adapted to 10 grams per liter NaCl was influenced by the stage of growth, with the highest degree of tolerance exhibited by cells in the exponential phase. Cell osmotic potential and turgor varied through the growth cycle of unadapted cells and cells at all levels of adaptation, with maximum turgor occurring at approximately the onset of exponential fresh weight accumulation.Adaptation to NaCl led to reduced cell expansion and fresh weight gain, while dry weight gain remained unaffected. This reduction in cell expansion was not due to failure of the cells to maintain turgor since cells adapted to NaCl underwent osmotic adjustment in excess of the change in water potential caused by the addition of NaCl to the medium. Tolerance of the adapted cells, as indicated by fresh or dry weight gain, did not increase proportionately with the increase in turgor. Adaptation of these glycophytic cells to NaCl appears to involve mechanisms which result in an altered relationship between turgor and cell expansion.

Journal Article↗
PubMed1988

Intracellular compartmentation of ions in salt adapted tobacco cells.

Na(+) and Cl(-) are the principal solutes utilized for osmotic adjustment in cells of Nicotiana tabacum L. var Wisconsin 38 (tobacco) adapted to NaCl, accumulating to levels of 472 and 386 millimolar, respectively, in cells adapted to 428 millimolar NaCl. X-ray microanalysis of unetched frozen-hydrated cells adapted to salt indicated that Na(+) and Cl(-) were compartmentalized in the vacuole, at concentrations of 780 and 624 millimolar, respectively, while cytoplasmic concentrations of the ions were maintained at 96 millimolar. The morphometric differences which existed between unadapted and salt adapted cells, (cytoplasmic volume of 22 and 45% of the cell, respectively), facilitated containment of the excited volume of the x-ray signal in the cytoplasm of the adapted cells. Confirmation of ion compartmentation in salt adapted cells was obtained based on kinetic analyses of (22)Na(+) and (36)Cl(-) efflux from cells in steady state. These data provide evidence that ion compartmentation is a component of salt adaptation of glycophyte cells.

Journal Article↗