The role of putative glycosylation sites in the extracellular loops of the vasopressin V1a receptor.
Explore the source record for details and available documents.
Animals↗
Biomedical subjects
G Matthews
Publications and source records attributed to G Matthews.
A randomised placebo controlled trial of loop diuretics in moderate/severe pre-eclampsia, following delivery.
Nineteen patients with pre-eclampsia were randomised to receive 40 mg of frusemide or placebo by mouth daily for 7 days in the first post-partum week. Outcome measures included mean and maximum blood pressure, the need for additional antihypertensive treatment during that period and mean length of hospital stay. There were no statistically significant differences in outcome between the treatment and placebo groups although there was a trend to more rapid lowering of blood pressure following delivery in those receiving frusemide.
Journal Article↗
A case of maternal pelvic trauma following a road traffic accident, associated with fetal intracranial haemorrhage.
Maternal pelvic injury resulting from road traffic accidents may cause fetal intracranial haemorrhage. A case is described. Caesarean section should be considered in acute trauma.
Accidents, Traffic↗
Static and dynamic membrane properties of large-terminal bipolar cells from goldfish retina: experimental test of a compartment model.
Capacitance measurements allow direct studies of exocytosis and endocytosis in single synaptic terminals isolated from bipolar neurons of goldfish retina. Extending the technique to intact bipolar cells, with their more complex morphology, requires information about the cells' electrotonic architecture. To this end, we developed a compartment model of bipolar neurons isolated from goldfish retina and tested the model experimentally. The isolated cells retained morphology similar to that of bipolar neurons in intact goldfish retina. In whole cell recordings, current relaxations in response to 10-mV hyperpolarizing voltage pulses decayed with a biexponential time course. This suggests that the cells may be described by a two-compartment equivalent circuit with compartments corresponding to the soma/dendrites (6-10 pF) and synaptic terminal (2-4 pF), linked by the axial resistance (30-60 M omega) of the axon. Four lines of evidence validate the equivalent circuit. 1) Similar estimates of somatic/dendritic and terminal capacitance were obtained whether the patch pipette was attached to the soma or to the synaptic terminal. 2) Estimates of the capacitance of the two compartments in intact cells were similar to estimates from somata and terminals that were isolated by cleavage of the connecting axon. 3) When current transients were generated from a more complete computer simulation of a bipolar neuron, analysis of the simulated transients with the use of the simple two-compartment model yielded capacitance estimates similar to those used to set up the simulation. 4) In isolated cells, the model gave estimates of depolarization-evoked increases in capacitance of the synaptic terminal that were quantitatively similar to those measured in terminals that were detached from the rest of the cell. Although in previous studies researchers have attempted to apply a similar equivalent circuit to more geometrically complex cells, morphological correlates of the equivalent-circuit compartments have been elusive. Our results demonstrate that in dissociated bipolar cells, precise morphological correlates can be assigned to the equivalent-circuit compartments. Additionally, the work shows that time-resolved capacitance measurements of synaptic transmitter release are possible in intact, isolated bipolar neurons and may also be feasible in intact tissue.
Animals↗
Evidence that vesicles on the synaptic ribbon of retinal bipolar neurons can be rapidly released.
We relate the ultrastructure of the giant bipolar synapse in goldfish retina to the jump in capacitance that accompanies depolarization-evoked exocytosis. Mean vesicle diameter is 29 +/- 4 nm, giving 26.4 aF/vesicle, so the maximum evoked capacitance (150 fF within 200 ms) represents fusion of about 5700 vesicles. Two terminals contained, respectively, 45 and 65 ribbon-type synaptic outputs, and a fully loaded ribbon tethers about 110 vesicles. Thus, the tethered pool, about 6000 vesicles, corresponds to the rapidly released pool. Further, the difference between small and large terminals in number of tethered vesicles matches their difference in capacitance jump. This suggests, within a "fire and reload" model of exocytosis, that the ribbon translocates synaptic vesicles very rapidly to membrane docking sites, supporting a maximum release rate of 500 vesicles/active zone/s, until the population of tethered vesicles is exhausted.
Animals↗
Ultrafast exocytosis elicited by calcium current in synaptic terminals of retinal bipolar neurons.
Using high resolution capacitance measurements, we have characterized an ultrafast component of transmitter release in ribbon-type synaptic terminals of retinal bipolar neurons. During depolarization, capacitance increases to a plateau of approximately 30 fF with a time constant of approximately 1.5 ms. When not limited by activation kinetics of calcium current, the small pool is depleted even faster, with a time constant of 0.5 ms. After the ultrafast pool is depleted, capacitance rises with a slower time constant of approximately 300 ms. EGTA (5 mM) depresses the slower capacitance rise but leaves the ultrafast phase intact. BAPTA (5 mM) depresses both components of exocytosis. With paired-pulse stimulation, the ultrafast pool recovers from depletion with a time constant of approximately 4 s. The ultrafast component may represent fusion of docked vesicles at the base of the synaptic ribbon, while the slower component represents more distal vesicles on the ribbon.
Animals↗
Synaptic exocytosis and endocytosis: capacitance measurements.
Exo- and endocytosis are accompanied by changes in membrane capacitance. Capacitance measurements in synaptic terminals have proven recently to be a useful adjunct to other techniques in examining presynaptic mechanisms. New information has emerged from these studies about the size and dynamics of synaptic vesicle pools, about the Ca2+ dependence of the rate of exocytosis, and about the kinetics of endocytosis in synaptic terminals.
Animals↗
Laparoscopic cholecystectomy for recurrent gallstone pancreatitis during pregnancy.
A pregnant patient with gallstone-induced pancreatitis initially responded to medical treatment, but the pancreatitis recurred. Endoscopic retrograde cholangiopancreatography and laparoscopic cholecystectomy were done at 28 weeks' gestation. The remainder of the pregnancy was unremarkable. Although 20 cases of laparoscopic cholecystectomy have been reported for cholecystitis during pregnancy, this is the first report of laparoscopic management of recurrent gallstone pancreatitis in a pregnant patient.
Adult↗
Age and gender differences in perceived accident likelihood and driver competences.
Road traffic accident involvement rates show clear age and gender differences which may in part be accounted for by differences in risk perception and perceptions of driving competence. The present study extends and replicates that of Matthews and Moran (1986). Young (18-30 years) and older (45-60 years) male and female drivers responded to a questionnaire on perceived accident risk and driving competence (judgment and skill) with respect to themselves and four target groups, and also rated a series of videotaped driving sequences with respect to likelihood of accident occurrence and perceived driving competence. Results showed that effects of rater characteristics were generally confined to the questionnaire. Younger males were perceived as most likely to experience an accident and were judged to be lower than other groups in driving competence. Younger groups showed little bias against older groups and vice versa, but gender-related bias was apparent. The findings of Matthews and Moran were generally confirmed. The results are discussed with reference to four main issues: (1) demographic bias effects--which are generally weak; (2) stereotyping on the basis of gender and/or age of driver; (3) group-specific bias; (4) self-appraisal bias.
Accidents, Traffic↗
Neurotransmitter release.
Synaptic vesicle exocytosis is rapid and highly localized, which are features that arise from the organization of the presynaptic active zone, where vesicle fusion occurs. Colocalization of calcium channels with the proteins making up the vesicle docking machinery at the active zone, combined with the low affinity and high cooperativity of the calcium sensor for vesicle fusion, allows vesicles to fuse with short delay after a presynaptic action potential. Evidence suggests that the calcium concentration driving synaptic vesicle fusion corresponds to the high level (50-100 muM) achieved only within the microdomain of elevated calcium near the inner mouth of open calcium channels. Retrieval of synaptic vesicle membrane by endocytosis is also regulated by internal calcium but at much lower concentrations. Endocytosis occurs rapidly after exocytosis if internal calcium is near the basal level but is inhibited by elevated internal calcium (0.5-1.0 muM).
Action Potentials↗
Calcium-dependent inactivation of calcium current in synaptic terminals of retinal bipolar neurons.
Giant synaptic terminals (approximately 10 micrometer diameter) of bipolar neurons from goldfish retina were used to directly investigate calcium-dependent inactivation of presynaptic calcium current. During sustained depolarization, calcium current was initially constant for a period lasting up to several hundred milliseconds and then it declined exponentially. The duration of the initial delay was shorter and the rate of inactivation was faster with larger calcium current. The fastest time constant of inactivation (in the range of 2-5 sec) was observed under weak calcium buffering conditions. Inactivation was attenuated when external Ca2+ was replaced with Ba2+ and when terminals were dialyzed with high concentrations of internal BAPTA. Elevation of intracellular calcium concentration ([Ca2+]i) by application of the calcium ionophore ionomycin or by dialysis with pipette solutions containing buffered elevated [Ca2+] produced inactivation of calcium current. The rate of recovery from inactivation was not determined by the recovery of [Ca2+]i to baseline after a stimulus. The results demonstrate that the presynaptic calcium current in bipolar neurons is inactivated by elevated [Ca2+]i, but the inactivation is approximately 100-fold slower than previously described calcium-dependent inactivation in other types of cells.
Animals↗
Differences in pH optima and calcium requirements for maturation of the prohormone convertases PC2 and PC3 indicates different intracellular locations for these events.
PC2 and PC3, which is also known as PC1, are subtilisin-like proteases that are involved in the intracellular processing of prohormones and proneuropeptides. Both enzymes are synthesized as propolypeptides that undergo proteolytic maturation within the secretory pathway. An in vitro translation/translocation system from Xenopus egg extracts was used to investigate mechanisms in the maturation of pro-PC3 and pro-PC2. Pro-PC3 underwent rapid (t1/2 < 10 min) processing of the 88-kDa propolypeptide at the sequence RSKR83 to generate the 80-kDa active form of the enzyme. This processing was blocked when the active site aspartate was changed to asparagine, suggesting that an autocatalytic mechanism was involved. In this system, processing of pro-PC3 was optimal between pH 7.0 and 8.0 and was not dependent on additional calcium. These results are consistent with pro-PC3 maturation occurring at an early stage in the secretory pathway, possibly within the endoplasmic reticulum, where the pH would be close to neutral and the calcium concentration less than that observed in later compartments. Processing of pro-PC2 in the Xenopus egg extract was much slower than that of pro-PC3 (t1/2 = 8 h). It exhibited a pH optimum of 5.5-6.0 and was dependent on calcium (K0.5 = 2-4 mM). The enzymatic properties of pro-PC2 processing were similar to that of the mature enzyme. Further studies using mutant pro-PC2 constructs suggested that cleavage of pro-PC2 was catalyzed by the mature 68-kDa PC2 molecule. The results were consistent with pro-PC2 maturation occurring within a late compartment of the secretory pathway that contains a high calcium concentration and low pH.
Amino Acid Sequence↗
Swelling activates chloride current and increases internal calcium in nonpigmented epithelial cells from the rabbit ciliary body.
Membrane current and [Ca]i in rabbit nonpigmented ciliary body epithelial cells (NPE cells) were monitored with combined patch-clamp and fura-2 measurements during cell swelling induced by anisosmotic conditions. In the presence of K-channel blockers, cell swelling produced an increase in membrane current, accompanied by an increase in [Ca]i. Structural changes in the cell, associated with membrane deformation, may be the cause of the increase in [Ca]i during swelling. The conductance activated by swelling was permeable to Cl: it was dependent on the Cl concentration gradient across the cell membrane, and it was blocked by the Cl-channel blockers DIDS, SITS, NPPB, and DIOA. Although swelling increased both Cl current and [Ca]i, there was no evidence that Ca was involved in the regulation of the Cl conductance. Cell swelling activated the current even when [Ca]i was strongly buffered at an elevated level (500 nM) or at a low level (approximately 0) with internal Ca-BAPTA/Cs-BAPTA mixtures. In addition, Cl conductance was unaffected when [Ca]i was increased with a Ca ionophore. There was also no evidence that cAMP participates in the regulation of the Cl conductance: swelling activation of the current occurred in the presence of cAMP inhibitor (Rp-cAMP-S) and cAMP mimic (Sp-cAMP-S). The data suggest independent involvement of Cl conductance and internal Ca in the regulation of cell volume in NPE cells.
Animals↗
Characterisation of Krp1, an endopeptidase that is essential for cell viability in fission yeast.
Explore the source record for details and available documents.
Amino Acid Sequence↗
Isolation and characterization of krp, a dibasic endopeptidase required for cell viability in the fission yeast Schizosaccharomyces pombe.
The activation of pro-hormones and many precursor proteins involves cleavage by endopeptidases belonging to the subtilisin-like family of enzymes. Here we describe the isolation and characterization of the first member of this family from the fission yeast Schizosaccharomyces pombe. The enzyme, which has been named krp for KEX2-related protease, is a type I membrane-bound endopeptidase that cleaves substrates after pairs of dibasic residues. It appears to be synthesized as a pre-pro-protein that is likely to undergo processing following translocation into the endoplasmic reticulum. Processing has been characterized in a cell-free translation/translocation system prepared from Xenopus eggs. Krp is N-glycosylated on all five of its potential sites and both the pre-sequence and the pro-sequence are quickly removed following translocation, the latter probably by autocatalytic cleavage. The inhibitor profile of krp broadly reflects the known properties of the eukaryotic subtilisin proteases, while its pH and Ca2+ dependence are consistent with it being active within the secretory pathway. One of its physiological substrates is likely to be the pheromone precursor pro-P-factor, which it is shown to process in an in vitro system, but identification of other substrates is complicated because, unlike other members of this family, krp is essential for cell viability.
Amino Acid Sequence↗
Calcium dependence of the rate of exocytosis in a synaptic terminal.
Rapid calcium-dependent exocytosis underlies neurotransmitter release from nerve terminals. Despite the fundamental importance of this process, neither the relationship between presynaptic intracellular calcium ion concentration ([Ca2+]i) and rate of exocytosis, nor the maximal rate of secretion is known quantitatively. To provide this information, we have used flash photolysis of caged Ca2+ to elevate [Ca2+]i rapidly and uniformly in synaptic terminals, while measuring membrane capacitance as an index of exocytosis and monitoring [Ca2+]i with a Ca(2+)-indicator dye. When [Ca2+]i was abruptly increased to > 10 microM, capacitance rose at a rate that increased steeply with [Ca2+]i. The steepness suggested that at least four calcium ions must bind to activate synaptic vesicle fusion. Half-saturation was at 194 microM, and the maximal rate constant was 2,000-3,000 s-1. A given synaptic vesicle can exocytose with high probability within a few hundred microseconds, if [Ca2+]i rises above 100 microM. These properties provide for the extremely rapid signalling required for neuronal communication.
Acetates↗
Inhibition of endocytosis by elevated internal calcium in a synaptic terminal.
During synaptic transmission in the nervous system, synaptic vesicles fuse with the plasma membrane of presynaptic terminals, releasing neurotransmitter by exocytosis. The vesicle membrane is then retrieved by endocytosis and recycled into new transmitter-containing vesicles. Exocytosis in synaptic terminals is calcium-dependent, and we now report that endocytosis also is regulated by the intracellular calcium concentration ([Ca2+]i). Capacitance measurements in synaptic terminals of retinal bipolar neurons revealed that endocytosis was strongly inhibited by elevated [Ca2+]i in the range achieved by Ca(2+)-current activation. The rate of membrane retrieval was steeply dependent on [Ca2+]i, with a Hill coefficient of 4 and half-inhibition at approximately 500 nM. At [Ca2+]i > or = 900 nM, endocytosis was entirely absent. The action of internal calcium on endocytosis represents a novel negative-feedback mechanism controlling the rate of membrane recovery in synaptic terminals after neurotransmitter secretion. As membrane retrieval is the first step in vesicle recycling, this mechanism may contribute to activity-dependent synaptic depression.
Animals↗
Voltage-dependent sodium channels develop in rat retinal pigment epithelium cells in culture.
Whole-cell patch-clamp recordings were made from isolated cells of the retinal pigment epithelium (RPE) of neonatal rats. After 24 hr in cell culture, RPE cells developed a transient, voltage-activated inward current that was never observed in acutely isolated cells. The kinetics, voltage-dependence, and reversal potential of the current and its dependence on external sodium demonstrated that the current was due to the expression of voltage-activated Na+ channels in cultured RPE cells. The current was partly blocked by tetrodotoxin at low concentrations (< 100 nM), but a second component of Na+ current was unblocked by tetrodotoxin at concentrations up to 10 microM. Na+ channels were present in cultured RPE cells at sufficient density to support regenerative action potentials in voltage recordings. Both the epithelial cells of the RPE and the neurons of the retina derive embryonically from neural origin, and it is known that under certain circumstances, nonmammalian RPE cells retain the ability to take on neuronal characteristics. The development of voltage-activated Na+ channels and the presence of action potentials demonstrate that neonatal mammalian RPE cells are also capable of expressing neuronal characteristics in cell culture.
Animals↗