Biomedical subjects

Peter D Brown

Publications and source records attributed to Peter D Brown.

8 recordsLinked to original sources

PubMed2006

Glucose-induced swelling in rat pancreatic alpha-cells.

Pancreatic beta-cells increase in volume when exposed to elevated concentrations of extracellular glucose. This study has examined the effects of glucose on the volumes of pancreatic alpha-cells, which like beta-cells are regulated by glucose, and intestinal epithelial Caco-2 cells which are unresponsive to glucose. Cell volume changes were monitored by a video-imaging method. Increasing the extracellular glucose concentration caused a concentration-dependent increase in alpha-cell volume over the range 1-20mM. Glucose-induced swelling was not, however, observed in Caco-2 cells. The glucose-induced swelling in both alpha- and beta-cells was abolished by 0.5mM phloretin, an inhibitor of the GLUT proteins, indicating that GLUT mediated glucose transport is a pre-requisite for swelling. Glucose metabolism also appears to be essential, as islet cell swelling was not observed with 16 mM 3-O-methyl glucose. These data suggest that glucose-induced swelling may be a property exclusive to glucose-regulated cells.

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PubMed2005

Flecainide overdose--support using an intra-aortic balloon pump.

BACKGROUND: Flecainide is an antiarrhythmic agent which is being used increasingly for the management of super-ventricular arrhythmias. Overdose with flecainide is frequently fatal with mortality reported as high as 22% due to arrhythmias, myocardial depression and conduction defects leading to electro-mechanical dissociation and asytole. Supportive measures are often required during the case and previously have included inotropes, extracorporeal membrane oxygenation and cardiopulmonary bypass. CASE PRESENTATION: A 47 year old lady presented to the emergency department with a four hour history of severe central chest pain. Her ECG showed atrial fibrillation and broad QRS complexes with a sine wave appearance. She had a past history of paroxysmal atrial fibrillation and significant psychiatric history. Following thrombolysis for a presumed myocardial infarction she developed cardiogenic shock with severely impaired left ventricular function. An intra-aortic balloon pump was inserted and coronary angiography demonstrated normal coronary arteries. With inotropic support she improved over 48 hours, with both her QRS duration and left ventricular function returning to normal. Biochemical testing following her discharge demonstrated significantly elevated levels of flecainide. CONCLUSION: The use of an intra-aortic balloon pump is a useful supportive measure during the acute phase of flecainide overdose associated with severe myocardial depression.

Journal Article↗

PubMed2004

Expression of K+-Cl- cotransporters in the alpha-cells of rat endocrine pancreas.

The expression of K+-Cl- cotransporters (KCC) was examined in pancreatic islet cells. mRNA for KCC1, KCC3a, KCC3b and KCC4 were identified by RT-PCR in islets isolated from rat pancreas. In immunocytochemical studies, an antibody specific for KCC1 and KCC4 revealed the expression of KCC protein in alpha-cells, but not pancreatic beta-cells nor delta-cells. A second antibody which does not discriminate among KCC isoforms identified KCC expression in both alpha-cell and beta-cells. Exposure of isolated alpha-cells to hypotonic solutions caused cell swelling was followed by a regulatory volume decrease (RVD). The RVD was blocked by 10 microM [dihydroindenyl-oxy] alkanoic acid (DIOA; a KCC inhibitor). DIOA was without effect on the RVD in beta-cells. NEM (0.2 mM), a KCC activator, caused a significant decrease of alpha-cell volume, which was completely inhibited by DIOA. By contrast, NEM had no effects on beta-cell volume. In conclusion, KCCs are expressed in pancreatic alpha-cells and beta-cells. However, they make a significant contribution to volume homeostasis only in alpha-cells.

Animals↗

PubMed2004

Ion channels in epithelial cells of the choroid plexus isolated from the lateral ventricle of rat brain.

Whole-cell patch clamp methods were used to determine the expression of ion channels in the epithelial cells of choroid plexus isolated from the lateral ventricle of the rat brain. A single population of cells with a mean capacitance of 61.5+/-1.7 pF was identified in 103 recordings. This value is significantly greater than that measured for cells from the fourth ventricle (P<0.01 by unpaired t-test), indicating that cells from the lateral ventricle have a greater surface area. Voltage-dependent, outward currents were recorded using a K(+)-rich electrode solution. These currents were partially inhibited by 10 nM margatoxin or 10 nM dendrotoxin-K and blocked by 5 mM TEA(+). An inward-rectifying chloride conductance was observed in K(+)-free solutions. The relative permeability of this conductance to anions was P(I)>P(Cl)>P(aspartate). A volume-sensitive anion conductance was observed when cell swelling was induced using a hypertonic electrode solution. The properties of each conductance were similar to conductances previously identified in fourth ventricle choroid plexus cells. Furthermore, there were no significant differences between the magnitudes of any of the conductances in cells from the lateral and fourth ventricle choroid plexus. Thus, the ionic conductances expressed in rat lateral and fourth ventricle choroid plexus are very similar.

Animals↗

PubMed2003

Kv1.1 and Kv1.3 channels contribute to the delayed-rectifying K+ conductance in rat choroid plexus epithelial cells.

The choroid plexuses secrete, and maintain the composition of, the cerebrospinal fluid. K+ channels play an important role in these processes. In this study the molecular identity and properties of the delayed-rectifying K+ (Kv) conductance in rat choroid plexus epithelial cells were investigated. Whole cell K+ currents were significantly reduced by 10 nM dendrotoxin-K and 1 nM margatoxin, which are specific inhibitors of Kv1.1 and Kv1.3 channels, respectively. A combination of dendrotoxin-K and margatoxin caused a depolarization of the membrane potential in current-clamp experiments. Western blot analysis indicated the presence of Kv1.1 and Kv1.3 proteins in the choroid plexus. Furthermore, the Kv1.3 and Kv1.1 proteins appear to be expressed in the apical membrane of the epithelial cells in immunocytochemical studies. The Kv conductance was inhibited by 1 microM serotonin (5-HT), with maximum inhibition to 48% of control occurring in 8 min (P < 0.05 by Student's t-test for paired data). Channel inhibition by 5-HT was prevented by the 5-HT2C antagonist mesulergine (300 nM). It was also attenuated in the presence of calphostin C (a protein kinase C inhibitor). The conductance was partially inhibited by 1,2-dioctanoyl-sn-glycerol and phorbol 12-myristate 13-acetate, both of which activate protein kinase C. These data suggest that 5-HT acts at 5-HT2C receptors to activate protein kinase C, which inhibits the Kv channels. In conclusion, Kv1.1 and Kv1.3 channels make a significant contribution to K+ efflux at the apical membrane of the choroid plexus.

Animals↗

PubMed2003

Capsaicin modulates K+ currents from dissociated rat taste receptor cells.

Chili pepper is one of most widely used spices. The main active component of chili pepper is the capsaicin. The effects of capsaicin on sensory nerve endings are well known; however, little is known regarding the direct effect of capsaicin on taste receptor cells (TRCs). In this study, patch clamp methods were used to study the effects of capsaicin on the K(+) currents in TRCs isolated from the rat circumvallate papilla. Fura-2 microspectrofluorimetry was also used to determine the effects of capsaicin on the intracellular Ca(2+) concentration ([Ca(2+)](i)). In the resting state, whole-cell experiments identified outward-rectifying K(+) currents, which were inhibited by 5 mM tetraethylammonium (TEA(+)) chloride. Voltage-dependent K(+) channels with a conductance of 55+/-4 pS (mean+/-S.E.M.; n=3), were observed in cell-attached patches. Capsaicin (500 nM) completely inhibited the outward-rectifying K(+) current in the whole-cell recordings. In cell-attached patches 500 nM capsaicin significantly reduced the open probability (P(o)) of the K(+) channels from 0.401+/-0.052 (n=3) in the resting state, to 0.018+/-0.002 (n=3, P<0.05 by unpaired t-test). In the fura-2-loaded TRCs, micromolar concentrations of capsaicin increased [Ca(2+)](i) in a dose-dependent manner, e.g., 100 microM capsaicin consistently increased the 340:380 fluorescence ratio from 1.04+/-0.05 in the resting state to 1.40+/-0.05 (n=28). These results suggest that capsaicin can enhance or modify the gustatory sensation by inhibiting the K(+) currents of the TRCs directly.

Animals↗

PubMed2003

Expression of aquaporin 1 and aquaporin 4 water channels in rat choroid plexus.

The role of aquaporins in cerebrospinal fluid (CSF) secretion was investigated in this study. Western analysis and immunocytochemistry were used to examine the expression of aquaporin 1 (AQP1) and aquaporin 4 (AQP4) in the rat choroid plexus epithelium. Western analyses were performed on a membrane fraction that was enriched in Na(+)/K(+)-ATPase and AE2, marker proteins for the apical and basolateral membranes of the choroid plexus epithelium, respectively. The AQP1 antibody detected peptides with molecular masses of 27 and 32 kDa in fourth and lateral ventricle choroid plexus. A single peptide of 29 kDa was identified by the AQP4 antibody in fourth and lateral ventricle choroid plexus. Immunocytochemistry demonstrated that AQP1 is expressed in the apical membrane of both lateral and fourth ventricle choroid plexus epithelial cells. The immunofluorescence signal with the AQP4 antibody was diffusely distributed throughout the cytoplasm, and there was no evidence for AQP4 expression in either the apical or basolateral membrane of the epithelial cells. The data suggest that AQP1 contributes to water transport across the apical membrane of the choroid plexus epithelium during CSF secretion. The route by which water crosses the basolateral membrane, however, remains to be determined.

Animals↗

PubMed2002

Inward-rectifying anion channels are expressed in the epithelial cells of choroid plexus isolated from ClC-2 'knock-out' mice.

Choroid plexus epithelial cells express inward-rectifying anion channels which have a high HCO(3)(-) permeability. These channels are thought to have an important role in the secretion of cerebrospinal fluid. The possible relationship between these channels and the ClC-2 Cl(-) channel was investigated in the present study. RT-PCR, using specific ClC-2 primers, amplified a 238 bp fragment of mRNA from rat choroid plexus, which was 99 % identical to the 5' sequence of rat ClC-2. A 2005 bp clone was isolated from a rat choroid plexus cDNA library using a probe for ClC-2. The clone showed greater than 99 % identity with the sequence of rat ClC-2. Inward-rectifying anion channels were observed in whole-cell recordings of choroid plexus epithelial cells isolated from ClC-2 knock-out mice. The mean inward conductance was 19.6 plus minus 3.6 nS (n = 8) in controls (3 heterozygote animals), and 22.5 plus minus 3.1 nS (n = 10) in three knock-out animals. The relative permeability of the conductances to I(-) and Cl(-) (P(I) : P(Cl)) was determined. I(-) was more permeant than Cl(-) in both heterozygotes (P(I):P(Cl) = 4.0 +/- 0.9, n = 3) and knock-out animals (P(I) : P(Cl) = 4.1 +/- 1.4, n = 3). These results indicate that rat choroid plexus expresses the ClC-2 variant that was originally reported in other tissues. ClC-2 does not contribute significantly to inward-rectifying anion conductance in mouse choroid plexus, which must therefore express a novel inward-rectifying anion channel.

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