Endoscopic view of cocaine rhinitis.
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Adult↗
Biomedical subjects
R Latorre
Publications and source records attributed to R Latorre.
Selectivity and gating properties of a cAMP-modulated, K(+)-selective channel from Drosophila larval muscle.
The selectivity and gating properties of cAMP-modulated, voltage-independent, K(+)-selective channel from Drosophila larval muscle were investigated using the patch-clamp technique. In symmetrical 115 mM K+ the channel displayed a linear current-voltage relation with slope conductance of 43 pS. Under biionic conditions (115 mM K+ pipette/115 mM X+ cytoplasmic) the permeability sequence was K+ > Rb+ > NH4+ >> Cs+,Na+. The channel was impermeable to Ca2+ (PCa/PK < 0.02). Under steady-state conditions and regardless [cAMP], open dwell times showed a double exponential distribution. [cAMP] did not affect the time constants of the two components of open times, or their relative amplitudes. Moreover, successive openings were correlated in open time. Closed dwell times were made of at least three exponential components. Fast application of cAMP to the cytoplasmic side of the channel induced a transient increase in open probability that relaxed to a lower value within seconds. This last result suggests that cAMP can activate and desensitize this cAMP-modulated, K(+)-selective channel.
Animals↗
External barium block of Shaker potassium channels: evidence for two binding sites.
External barium ions inhibit K+ currents of Xenopus oocytes expressing ShH4 delta 6-46, the non-inactivating deletion of the Shaker K+ channel. At the macroscopic level, Ba2+ block comprises both a fast and a slow component. The fast component is less sensitive to Ba2+ (apparent dissociation constant at 0 mV, K(0), approximately 19.1 mM) than the slow component and is also less voltage dependent (apparent electrical distance, delta, approximately 0.14). The slow component (K(0), approximately 9.4 mM, delta approximately 0.25) is relieved by outward K+ current, which suggests that the corresponding binding site resides within the channel conduction pathway. At the single channel level, the fast component of block is evidenced as an apparent reduction in amplitude, suggesting an extremely rapid blocking and unblocking reaction. In contrast, the slow component appears to be associated with long blocked times that are present from the beginning of a depolarizing command. Installation of the slow component is much slower than a diffusion limited process; for example, the blocking time constant (tau) produced by 2 mM Ba2+ is approximately 159 s (holding potential, HP = -90 mV). However, the blocking rate of this slow component is not a linear function of external Ba2+ and tends to saturate at higher concentrations. This is inconsistent with a simple bi-molecular blocking reaction. These features of external Ba2+ block can be accounted for by a simple model of two sequential Ba2+ binding sites, where the deeper of the two sites produces the slow component of block.
Animals↗
Molecular determinants of ion conduction and inactivation in K+ channels.
K+ channel-forming proteins can be grouped into three families that differ by the number of potential membrane-spanning segments. The largest of these families is composed of tetrameric channels with subunits containing six putative membrane-spanning segments (S1-S6). Inward rectifiers comprise a second family of K+ channels with subunits having two transmembrane domains (M1, M2). Monomers in the third family are proteins containing only one membrane-spanning segment, and they give origin to minK+ channels. Joining together segments S5 and S6 in the case of voltage-gated K+ channels and M1 and M2 in inward rectifiers, there is a highly conserved region with a hairpin shape called the H5 or P region. The P region, the loop connecting the S4 and S5 domains and the S6 transmembrane segment in Shaker-type K+ channels and the COOH-terminal in inward rectifiers, appears to play crucial roles in ion conduction. In Shaker K+ channels the NH2-terminal has been identified as responsible for fast inactivation (N-type inactivation). If the fast-inactivation gate is removed, a slower inactivation process persists, and its rate can be altered by mutations of amino acid residues forming part of the region in the neighborhood of the COOH-terminal (C-type inactivation). In this review we discuss the strategies followed to identify the different structures of K+ channels involved in ion conduction and inactivation processes and how they interplay.
Amino Acid Sequence↗
Ion channel classes in purified olfactory cilia membranes: planar lipid bilayer studies.
Ciliary membrane fragment fusion to planar lipid bilayers resulted in the insertion of four ion channel types. cAMP-activated, cation-selective channels could be detected only in the absence of Ca2+ and had a conductance of 23 pS. They exhibited an apparent dissociation constant (Kd) for the cyclic nucleotide of approximately 30 microM and an estimated permeability ratio (PNa/PK) of 2.4. The cAMP cation-selective channel coinserted with a K(+)-selective channel refractory to cAMP, Ca2+, and D-myo-inositol 1,4,5-trisphosphate. This K+ channel was voltage independent and exhibited open-conductance substates of 60 and 112 pS. cAMP was also found to modulate a novel K+ channel with a Kd = 140 microM. It displayed three nearly equally spaced open substates with conductances of 34, 80, and 130 pS. In the absence and in the presence of cAMP the probability of occurrence of the open substates was binomially distributed. A fourth channel type was a Ca(2+)-activated K+ channel with a conductance of 240 pS. It was blocked by charybdotoxin at nanomolar concentrations (Kd = 3 nM). These results add support to the idea that, besides cAMP-activated cation-selective channels, vertebrate chemosensory olfactory membranes possess an arrangement of ion channels.
Animals↗
Choking spells following septorhinoplasty secondary to displaced nasal packing.
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Adult↗
Characterization of and modulation by a beta-subunit of a human maxi KCa channel cloned from myometrium.
cDNAs encoding functional maxi KCa channel alpha-subunits (hslo) were cloned from human myometrium. Northern blot analysis revealed a high abundance of mRNA in human uterine smooth muscle. Calcium- and voltage-activated K+ currents were recorded from Xenopus laevis oocytes injected with hslo cRNA and compared with currents after reconstitution of oocyte membranes expressing cloned maxi KCa channels. The expressed channels displayed characteristics of native maxi KCa channels, including large conductance (280 pS in symmetrical 110 mM K+), calcium sensitivity, kinetics and pharmacology. Currents were activated by niflumic acid; blocked by tetraethylammonium, charybdotoxin and iberiotoxin; and were insensitive to lemakalim, pinacidil, apamin and 4-aminopyridine. Coexpression with the beta-subunit, cloned from bovine trachea smooth muscle, dramatically increased the apparent calcium sensitivity as evident from a leftward shift of the voltage-activation curves. Half maximal activation (V1/2), measured in 10 microM Ca2+, was 12 +/- 18 mV (+/- SD, n = 62) for the alpha-subunit alone and -87 +/- 10 mV (+/- SD, n = 39) in presence of the beta-subunit.
Animals↗
Shaker mutants lack post-tetanic potentiation at motor end-plates.
The two-electrode voltage clamp technique was employed to measure end-plate currents in larval neuromuscular junctions of wild-type (Canton-S) and of three different Drosophila Shaker mutants: ShakerKS133, Shaker102 and f5Shaker5. In the Shaker mutants, nerve-evoked end-plate currents (neepc) were 4-5-fold larger than those measured in Canton-S. Shaker motor end-plates were found to lack post-tetanic potentiation (PTP), but could undergo facilitation. Moreover, PTP but not facilitation was lost in wild-type larvae if the neuromuscular junction was exposed to 4-aminopyridine (4-AP), a blocker of Shaker A-type K+ currents. End-plate currents were depressed by Ca2+ channel blockers like Mg2+, at millimolar concentrations, and Co2+ and Cd2+, at micromolar concentrations, but not by nifedipine (100 nM) and verapamil (100 nM). After exposure to Ca2+ channel blockers, Shaker end-plates exhibited PTP. In particular, Cd2+ was most effective in depressing neepcs and in restoring PTP in all Shaker mutants. The results obtained indicate the abnormal function of Shaker K+ channels at motor nerves specifically abolishes PTP in Drosophila larval neuromuscular junctions.
Animals↗
Structural determinants in the interaction of Shaker inactivating peptide and a Ca(2+)-activated K+ channel.
Shaker B inactivating peptide (BP) binds to its receptor in maxi KCa channels obstructing the flow of ions through them. The interaction between KCa channels and BP mutants, with different net charge and hydrophobicity, revealed several structural features of the KCa channel internal mouth. Increasing BP net positive charge or decreasing the internal milieu ionic strength increased the affinity and rate of association, while increasing hydrophobicity augmented blocking times and had limited or no effect on on-rates. These results uncover (a) the presence of negative charges in or near the BP receptor and (b) the existence of a hydrophobic contact surface in the internal channel vestibule that is a structural constituent of the BP receptor in maxi KCa channels.
Amino Acid Sequence↗
A simple model for surface charge on ion channel proteins.
We present a simple two-parameter model for surface charge directly associated with ion channels. A spherically symmetric "charged shell" models a distribution of surface charge arrayed about the channel entrance, with a corresponding set of image charges behind the plane of the membrane. The transition between a regime of buffered conductance and a regime of rapidly falling conductance at very low ionic strength is found to depend on the magnitude of the surface charge as well as the separation between the charge and the channel entrance. This resolves an apparent discrepancy between the experimental findings of Naranjo and Latorre (1993. Biophys. J. 64:1038-1050) and previous theoretical computations. The charged-shell model is used in a comparative study of the toad skeletal muscle conductance data of Naranjo and Latorre, the rat skeletal muscle conductances of Ravindran et al. (1992. Biophys. J. 61:494-508), and a second set of rat muscle conductances presented in this paper.
Animals↗
Endoscopic bile duct stone removal prior to laparoscopic cholecystectomy.
Of 1049 patients referred for laparoscopic cholecystectomy (LC) for symptomatic gallstone disease, 67 (6%) had clinical, biochemical, or echographic findings suggesting common bile duct stones. Patients in this group were studied preoperatively with endoscopic retrograde cholangiopancreatography (ERCP). In 26 patients (39%), the diagnosis was confirmed. In 12 other cases (18%), the macroscopic finding of a stripped or bleeding papilla without common bile duct stones suggested stone migration. ERCP in the remaining 29 patients (43%) was normal. Thirty-four endoscopic sphincterotomies (ES) were performed, 26 for common bile duct stones and 8 for cystic lithiasis or gallbladder microlithiasis. In the entire group of patients with choledocholithiasis, stone removal was possible. All 67 patients underwent laparoscopic cholecystectomy on an average of 2.8 days following the endoscopic procedure. Twenty-one patients (31%) had acute cholecystitis, and 5 had chronic scleroatrophic cholecystitis. Five (7.5%) of the 67 patients were converted to an open procedure. In 10 cases (16%), the cystic diameter was larger than an 8-mm M-L clip, which made necessary the use of endoligature or extra clips. No complications or deaths resulted from ERCP or ES. Two of the 62 patients (3.2%) who underwent LC had to be reoperated on, 1 because of a right subphrenic collection, and the other because of bilious ascites. No common bile duct lesions or deaths resulted in the analyzed group. The average hospitalization time, with the exception of those patients converted or reoperated on, was 8 days.
Adolescent↗
Postnatal development of semitendinosus muscle in the dog.
In this study the differentiation of postnatal muscle fibres in dog semitendinosus muscle has been characterized. Several histochemical techniques for myosin ATPase and metabolic activity were used in animals aged between 1 day and 2 months. The results show that at birth there are two types of fibre, whose ATPase activity gradually changes during postnatal development, so that several types of fibre can be identified after 2 months. These finally become the four types of the adult: I, IIA, IIDog, IIC. The main conclusions of the study are that the use of mATPase techniques is appropriate for showing the differentiation between muscle fibres, even at early stages of postnatal development, and that the origin of the four different fibres of the adult can be traced back to early postnatal stages.
Age Factors↗
Ion conduction in substates of the batrachotoxin-modified Na+ channel from toad skeletal muscle.
Batrachotoxin-modified Na+ channels from toad muscle were inserted into planar lipid bilayers composed of neutral phospholipids. Single-channel conductances were measured for [Na+] ranging between 0.4 mM and 3 M. When membrane preparations were made in the absence of protease inhibitors, two open conductance states were identified: a fully open state (16.6 pS in 200 mM symmetrical NaCl) and a substate that was 71% of the full conductance. The substate was predominant at [Na+] > 65 mM, whereas the presence of the fully open state was predominant at [Na+] < 15 mM. Addition of protease inhibitors during membrane preparation stabilized the fully open state over the full range of [Na+] studied. In symmetrical Na+ solutions and in biionic conditions, the ratio of amplitudes remained constant and the two open states exhibited the same permeability ratios of PLi/PNa and PCs/PNa. The current-voltage relations for both states showed inward rectification only at [Na+] < 10 mM, suggesting the presence of asymmetric negative charge densities at both channel entrances, with higher charge density in the external side. An energy barrier profile that includes double ion occupancy and asymmetric charge densities at the channel entrances was required to fit the conductance-[Na+] relations and to account for the rectification seen at low [Na+]. Energy barrier profiles differing only in the energy peaks can give account of the differences between both conductance states. Estimation of the surface charge density at the channel entrances is very dependent on the ion occupancy used and the range of [Na+] tested. Independent evidence for the existence of a charged external vestibule was obtained at low external [Na+] by identical reduction of the outward current induced by micromolar additions of Mg2+ and Ba2+.
Animals↗
[Chronology of the postnatal ossification of the shoulder and elbow joints in the Siamese cat (Felis catus L.)].
A study was done by radiological techniques to show the chronology of ossification of the shoulder and cubit joints in the Siam cat, from birth up to the 25th week of postnatal development. For this experiment we used 40 little cats (19 males and 21 females) belonging to 11 litters subjected to different controls: pattern race, healthy, feeding, growing up and radioactivity. The time of the appearance and the evolution of the ossification centers is determined as well as the phenomenon of fusion during this time. The postnatal ossification from both joints of the Siam cat is compared with that of the common cat.
Animals↗
[Chronology of the postnatal ossification of the thoracic limb in the Siamese cat (Felis catus L.)].
A study was done by radiological techniques to show the chronology of ossification of the thoracic autopodo of the Siam cat from birth up to the 25th week of postnatal development. For this experiment we used 40 little cats (19 males and 21 females) belonging to 11 litters subjected to different controls: pattern race, healthy, feeding, grow up and radioactivity. The time of the appearance and evolution of the centres that form the basipodo, metapodo and acropodo of the thoracic limb is determined. Likewise it is analyzed the phenomenon of fusion during that time to define the main ossification sequence in the carpo. The aspects of the postnatal ossification of the thoracic autopodo in the Siam cat are compared with the literature of different authors about the common cat.
Animals↗
Morphological and histochemical characteristics of muscle fibre types in the flexor carpi radialis of the dog.
The canine flexor carpi radialis is subdivided into 2 portions. The radial portion which occupies one third of the cross-section is located caudomedially and is composed only of large type I fibres (43.53 +/- 0.6 microns minimum diameter) in levels close to the insertion. The cubital portion is located craniolaterally and contains fewer and smaller type I fibres (26.10 +/- 0.3 microns minimum diameter). It is hypothesised that the radial portion of the muscle, with its larger slow fibre population, contributes to forelimb postural function. The cubital portion, with its generally fast fibre population (IIA), may be more important in the muscle's recognised function (flexion of the carpal joint during locomotion).
Adenosine Triphosphatases↗
Skeletal muscle fibre types in the dog.
Using a variety of histochemical methods we have investigated the mATPase reaction of skeletal muscle fibres in the dog. Types I, IIA, IIDog (peculiar to the dog) and IIC fibres were identified. The results reveal that the interpretation of the fibre type composition depends on the methods used.
Adenosine Triphosphatases↗
[Hepatitis B virus vaccine: early and late response in Chileans with high risk of infection].
BACKGROUND: Hepatitis B vaccine has demonstrated to be very effective and safe preventing hepatitis B virus infection. Long term protection induced by hepatitis B vaccination depends on the initial immune response and the declining rate of anti-HBs titers. AIM. To investigate early and late response to hepatitis B vaccine in a sample of high risk Chilean population. MATERIAL AND METHODS: Thirty one subjects (20 relatives of hepatitis B chronic carriers, 10 health service workers and one HIV seropositive) were vaccinated with a plasma derivated hepatitis B vaccine. Early and late response were estimated by anti-HBs titers. RESULTS: Twenty eight subjects (90%) produced protective titers of anti-HBs after 2 months from the third dose of vaccine (early response), and they remained at these levels in 75% of vaccinated individuals after three years (late response). All the subjects without protective titers after the three year follow up had produced anti-HBs levels lower than 300 UI at the early response. Hepatitis B vaccination was not associated with significant side effects. CONCLUSIONS: This experience confirms that hepatitis B vaccine is safe and effective inducing immunity in high risk subjects. Our data suggest that the early response to hepatitis B vaccine is able to identify those subjects requiring closer surveillance for boosters.
Adolescent↗