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L Best

Publications and source records attributed to L Best.

At least 19 recordsLinked to original sources
PubMed2005

Glucose-induced electrical activity in rat pancreatic beta-cells: dependence on intracellular chloride concentration.

A rise in glucose concentration depolarizes the beta-cell membrane potential leading to electrical activity and insulin release. It is generally believed that closure of KATP channels underlies the depolarizing action of glucose, though work from several laboratories has indicated the existence of an additional anionic mechanism. It has been proposed that glucose activates a volume-regulated anion channel, generating an inward current due to Cl- efflux. This mechanism requires that intracellular [Cl-] is maintained above its electrochemical equilibrium. This hypothesis was tested in rat beta-cells by varying [Cl-] in the patch pipette solution using the Cl--permeable antibiotic amphotericin B to allow Cl- equilibration with the cell interior. Under such conditions, a depolarization and electrical activity could be evoked by 16 mM glucose with pipette solutions containing 80 or 150 mM Cl-. At 40 or 20 mM Cl-, a subthreshold depolarization was usually observed, whilst further reduction to 12 or 6 mM abolished depolarization, in some cases leading to a glucose-induced hyperpolarization. With a pipette solution containing gramicidin, which forms Cl--impermeable pores, glucose induced a depolarization and electrical activity irrespective of [Cl-] in the pipette solution. Under the latter conditions, glucose-induced electrical activity was prevented by bumetanide, an inhibitor of the Na+-K+-2Cl- co-transporter. This inhibition could be overcome by the use of amphotericin B with a high [Cl-] pipette solution. These findings suggest that the maintenance of high intracellular [Cl-] in the beta-cell is an important determinant in glucose-induced depolarization, and support the hypothesis that beta-cell stimulation by glucose involves activation of the volume-regulated anion channel and generation of an inward Cl- current.

Amphotericin B↗
PubMed2004

Tolbutamide potentiates the volume-regulated anion channel current in rat pancreatic beta cells.

AIMS/HYPOTHESIS: Hypoglycaemic sulphonylureas are thought to stimulate insulin release by binding to a sulphonylurea receptor, closing K(ATP) channels and inducing electrical activity. However, the fact that these drugs stimulate insulin release at high glucose concentrations where K(ATP) channels are closed suggests additional ionic actions. The aim of this study was to test the hypothesis that sulphonylureas influence the current of the glucose- and volume-regulated anion channel. METHODS: Electrical and ion-channel activity were recorded in isolated rat beta cells using the patch-clamp technique. (86)Rb(+) efflux was measured using intact islets. Beta cell volume was measured using a video-imaging technique. RESULTS: In the absence of glucose, tolbutamide (100 micromol/l) transiently depolarised the cells. In the presence of glucose (5 mmol/l), tolbutamide evoked a sustained period of electrical activity, whilst at 10 mmol/l glucose, the drug evoked a pronounced 'silent' depolarisation. In the absence of glucose, tolbutamide inhibited (86)Rb(+) efflux. However, at 10 mmol/l glucose, tolbutamide induced a transient stimulation of efflux. Tolbutamide potentiated the whole-cell volume-regulated anion conductance in a glucose-dependent manner with an EC(50) of 85 micromol/l. In single channel recordings, tolbutamide increased the channel-open probability. Tolbutamide caused beta cell swelling in the presence of glucose, but not in its absence. CONCLUSIONS/INTERPRETATION: Tolbutamide can induce beta cell electrical activity by potentiating the glucose- and volume-regulated anion channel current. This effect is probably not due to a direct effect of the drug on the channel, but could be secondary to a metabolic action in the beta cell.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed2003

Neoadjuvant radiotherapy concurrent with weekly paclitaxel and carboplatin and followed by surgery in locally advanced non-small-cell lung cancer.

Thirty-seven patients were enrolled in a phase II study to evaluate the efficacy and toxicity of neoadjuvant radiotherapy concurrent with weekly paclitaxel and carboplatin in locoregionally advanced non-small-cell lung cancer (NSCLC). The study was also designed to evaluate the operability following concurrent chemoirradiation. The following response rates to chemoirradiation were obtained: complete response (CR) 5 of 37 (13.5%), partial response 14 of 37 (38%), stable disease 12 of 37 (32.5%) and PD 6 of 37 (16%). Twenty patients underwent surgery, and in 19 patients the tumor was totally resected. There was pathologic CR in 4 patients. Moderate/severe esophagitis developed in 16 patients (43%); hematologic toxicity was mild. There was one case of postoperative mortality. Nine patients are alive without evidence of disease at 5+ to 39+ months. Median survival is 22 months. It is concluded that neoadjuvant radiotherapy concurrent with weekly paclitaxel/carboplatin is effective and well tolerated in patients and feasible for patients with locally advanced NSCLC, allowing complete tumor resection in 56% of the cases.

Adult↗
PubMed2002

Evidence that glucose-induced electrical activity in rat pancreatic beta-cells does not require KATP channel inhibition.

KATP-channel activity, recorded in cell-attached patches from isolated rat pancreatic beta-cells, was found to be maximally inhibited in the presence of a substimulatory concentration (5 mM) of glucose, with no further effect of higher, stimulatory glucose concentrations. KATP channel-independent effects of glucose on electrical activity were therefore investigated by incubating cells in the presence of a supramaximal concentration of tolbutamide. Addition of tolbutamide (500 mM) to cells equilibrated in the absence of glucose resulted in a rapid depolarization and electrical activity followed by a gradual repolarization and disappearence of electrical activity. Repolarization was not due to desensitization of KATP channels to the sulfonylurea, but was probably the result of activation of another K+ conductance. The subsequent application of 16 mM glucose in the continued presence of tolbutamide depolarized the cells again, leading to renewed electrical activity. Input conductance of the cells was markedly reduced by tolbutamide, reflecting KATP-channel inhibition, but was not significantly affected by the addition of glucose in the presence of the drug. In cells voltage-clamped at -70 mV, addition of glucose in the presence of tolbutamide generated a noisy inward current, probably representing activation of the volume-sensitive anion channel. KATP channel-independent activation of electrical activity by glucose was inhibited by the anion channel inhibitor 4,4'-dithiocyanatostilbene-2,2'-disulphonic acid. It is concluded that the induction of electrical activity in rat pancreatic b-cells does not require inhibition of KATP channels. The KATP channel-independent mechanism could involve, at least in part, activation by glucose of the volume-sensitive anion channel.

Adenosine Triphosphate↗
PubMed2002

How does glucose evoke electrical activity in the pancreatic beta-cell?

In the absence of glucose, K(ATP) channel activity could be recorded in cell-attached patches. Addition of a sub-stimulatory concentration of glucose (5 mM) was sufficient to completely inhibit K(ATP) channel activity, and raising the glucose concentration to stimulatory levels (12 or 20 mM) had no further effect. Glucose was able to induce electrical activity and insulin release even when K(ATP) channel activity was completely inhibited by 0.5 mM tolbutamide. Glucose-induced electrical and secretory activity were, however, sensitive to inhibition by the anion channel blockers 4,4'-dithiocyanatostilbene-2,2'-disulphonic acid, 5-nitro-2-(3-phenylpropylamino) benzoic acid and 4-hydroxytamoxifen. A 200 pS anion-selective channel was identified in cell-attached patches generating an inward (depolarising) current at 0 mV pipette potential. The channel was activated by glucose over the range 4-20 mM. This channel is likely to be the volume-sensitive anion channel (VSAC) previously described in beta-cells. It is suggested that activation of the VSAC by stimulatory concentrations of glucose is the principal mechanism leading to depolarisation of the plasma membrane and hence electrical activity and insulin release. Channel activation requires glucose metabolism and could involve intracellular accumulation of metabolites and cell swelling. It is possible that the major role of the K(ATP) channel is in hyperpolarizing the cell, thus inhibiting electrical and secretory activity, during hypoglycaemia.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed2001

Linkage study in families with posterior helical ear pits and Wiedemann-Beckwith syndrome.

The Wiedemann-Beckwith syndrome (WBS) is defined by a group of anomalies, including macrosomia, macroglossia, omphalocele, and ear creases. Several minor anomalies have also been reported in the syndrome, including posterior helical ear pits (PHEP). Two independent linkage studies of pedigrees with autosomal dominant inheritance have shown linkage of WBS to 11p15.5 markers. Further confirming the location of WBS to this location is the finding of 11p15.5 duplications and translocations, as well as uniparental disomy for a small area of 11p15.5. In this study, members of previously described families exhibiting autosomal dominant inheritance of the PHEP phenotype were genotyped for three markers in the 11p15.5 region. These three markers were in the insulin-like growth factor (IGF2), insulin (INS), and tyrosine hydroxylase (TH) region. The data were examined by linkage analysis using the same genetic model used previously to demonstrate linkage of WBS to markers on chromosome 11p15.5: an autosomal dominant model with a penetrance of 0.90 and a gene frequency of 0.001. In one large pedigree, linkage analysis of the 11p15.5 markers excluded the PHEP phenotype from the IGF2, INS, and TH region. In the four other pedigrees examined, the marker loci were not sufficiently informative or the pedigrees did not provide sufficient power to exclude linkage from this region. The strongest evidence against linkage of the PHEP phenotype to 11p15.5 was evident by inspection of the segregation of the haplotypes of the markers in the pedigrees. In two informative pedigrees, relatives with the PHEP phenotype did not share the same haplotype of markers identical by descent. Our results show that the PHEP phenotype is not linked to chromosome 11p15.5 in the informative families tested. In the families examined, there are not enough individuals with WBS to determine if WBS was linked to 11p15.5 in these families. Although locus heterogeneity has not been demonstrated in WBS, it is possible that a second WBS locus exists and that the PHEP phenotype in these families is linked to a second WBS locus. Alternatively, the PHEP phenotype may occur independently of WBS so that the association of WBS and PHEP in our pedigrees may, in fact, represent causal heterogeneity.

Alleles↗
PubMed2001

Expression of volume-sensitive Cl(-) channels and ClC-3 in acinar cells isolated from the rat lacrimal gland and submandibular salivary gland.

1. The expression of ClC-3 was examined in rat lacrimal gland and submandibular salivary gland cells using RT-PCR and Western analysis. Whole-cell patch clamp methods were used to investigate the expression of volume-sensitive anion channels in acinar cells isolated from these tissues. 2. Expression of mRNA encoding ClC-3, and ClC-3 protein, was found in rat submandibular gland by RT-PCR and Western analysis. Rat lacrimal gland cells, however, did not appear to express mRNA encoding for ClC-3, nor the ClC-3 protein. 3. Volume-sensitive anion conductances were observed in both rat lacrimal gland and submandibular salivary gland acinar cells. The conductance was of a similar size in the two cell types, but was much slower to activate in the lacrimal cells. 4. The properties of the conductances in lacrimal and submandibular cells were similar, e.g. halide selectivity sequence (P(I) > P(Cl) > P(aspartate)) and inhibition by 4,4'-diisothiocyanostilbene-2,2'-disulphonic acid, 5-nitro-2-(3-phenylpropylamino)-benzoate and tamoxifen. 5. The data suggest that the expression of ClC-3 is not an absolute requirement for the activity of volume-sensitive anion channels in rat lacrimal gland acinar cells.

Animals↗
PubMed2001

Swelling-induced changes in cytosolic [Ca2++] in insulin-secreting cells: a role in regulatory volume decrease?

Exposure of insulin-secreting cells to hypotonic solutions causes cell swelling followed by regulatory volume decrease (RVD). We have previously demonstrated that RVD is due to activation of a Cl(-) conductance. The present study investigates whether changes in cytosolic [Ca(2+)] play a role in these responses. Hypotonic swelling of RINm5F insulinoma cells caused a marked increase in cytosolic [Ca(2+)]. This effect was abolished by omission of extracellular Ca(2+), by the Ca(2+) channel blockers D600 or Gd(3+)and by 4,4'-dithiocyanatostilbene-2,2'-disulphonic acid (DIDS), an inhibitor of the volume-sensitive anion. RVD was markedly impaired in the absence of extracellular Ca(2+), but not by D600 nor by Gd(3+). RVD was also inhibited by the maxi-K(+) (BK(Ca)) channel blockers tetraethylammonium (TEA) and iberiotoxin (IbTx), whereas the K(ATP) channel blocker tolbutamide was ineffective. Cell swelling was accompanied by activation of a K(+) conductance which was sensitive to TEA and IbTx but not to tolbutamide. It is concluded that cell swelling causes activation of the volume-sensitive anion channel, leading to depolarization and Ca(2+) entry via voltage-gated Ca(2+) channels. RVD is a Ca(2+)-dependent process, requiring low 'resting' levels of intracellular [Ca(2+)]. However, the swelling-induced increase in cytosolic [Ca(2+)] is not required for RVD to occur. RVD depends upon simultaneous activation of Cl(-) and K(+) channels. We suggest that the BK(Ca) channel is the major K(+) conductance involved in RVD.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed2001

Cytotoxic action of methylglyoxal on insulin-secreting cells.

Methylglyoxal is a spontaneous product of glucose metabolism which is known to have cytotoxic actions and to be present in raised concentrations in hyperglycaemia. It could therefore play an important role in glucose toxicity. We have investigated the cytotoxic effects of methylglyoxal on insulin-secreting cells, which are particularly sensitive to glucose toxicity. Methylglyoxal caused a concentration-dependent increase in the number of apoptotic RINm5F cells within 4-6 hours. A similar effect was observed with rat pancreatic beta-cells. tert-butylglyoxal, which is a poor substrate for the glyoxalase pathway, exerted a similar, though more potent apoptotic action. Dexamethasone and NaF were also found to induce apoptosis in RINm5F cells. Flow cytometric analysis suggested a degree of necrosis in addition to apoptosis resulting from treatment with methylglyoxal. The cytotoxic effect of methylglyoxal could contribute towards glucose toxicity in insulin-secreting cells.

Animals↗
PubMed2001

Expression of the Na+K+-2CI- cotransporter in alpha and beta cells isolated from the rat pancreas.

The expression of the Na+-K+-2Cl- cotransporter (NKCC1) in alpha cells and beta cells from the rat pancreas was examined. Isolated alpha cells and beta cells in a mixed islet cell preparation were identified by volume using video-imaging methods, and by the expression of glucagon or insulin. The expression of mRNA for NKCC1 in pancreatic islets was demonstrated by RT-PCR. Immunocytochemical studies showed that the NKCCI protein was expressed in rat beta cells, but not alpha cells. The activity of Na+-K+-2Cl- cotransporter was also examined, by studying cell volume regulation in response to HEPES-buffered, hypertonic solutions. A regulatory volume increase was observed in the beta cells but not the alpha cells. It is concluded that the NKCC1 is expressed in rat pancreatic beta cells but not alpha cells. This is consistent with the hypothesis that Cl- is accumulated above the expected equilibrium distribution in beta cells, but is below equilibrium in alpha cells.

Animals↗
PubMed2001

Hereditary hemorrhagic telangiectasia with pulmonary arteriovenous malformations.

BACKGROUND: Most congenital pulmonary arteriovenous malformations are associated with hereditary hemorrhagic telangiectasia. During pregnancy, pulmonary hemorrhage can occur, compromising maternal and fetal health. CASES: We studied three pregnancies in two women with hemorrhagic telangiectasia complicated by pulmonary arteriovenous malformations. A 28-year-old primigravida's fetus died at 25 weeks' gestation, and she had embolotherapy with coil springs, which corrected the hypoxemic state. In a subsequent pregnancy she delivered a healthy 2315-g infant at 38 weeks' gestation. A 19-year-old primigravida had spontaneous hemothorax at 26 weeks' gestation with severe hypoxemia and a growth-restricted fetus without umbilical artery diastolic flow. Pulmonary arteriovenous malformation was diagnosed by computed tomography of the maternal lung. She had continued pulmonary bleeding, so emergency lung lobectomy was done. Maternal hypoxemia and umbilical diastolic flow improved, and she had term delivery of a healthy 2250-g infant. CONCLUSION: Antenatal diagnosis and treatment of women with hereditary hemorrhagic telangectasia and pulmonary arteriovenous malformations might prevent potentially life-threatening fetomaternal complications.

Adult↗
PubMed2001

Functional characterisation of the volume-sensitive anion channel in rat pancreatic beta-cells.

The whole-cell and perforated patch configurations of the patch-clamp technique were used to characterise the volume-sensitive anion channel in rat pancreatic beta-cells. The channel showed high permeability (P ) relative to Cl(-) to extracellular monovalent organic anions (P(SCN)/P(Cll) = 1.73, P(acetate)/P(Cll) = 0.39, P(lactate)/P(Cll) = 0.38, P(acetoacetate)/P(Cll) = 0.32, P(glutamate)/P(Cll) = 0.28) but was less permeable to the divalent anion malate (P(malate)/P(Cll) = 0.14). Channel activity was inhibited by a number of putative anion channel inhibitors, including extracellular ATP (10 mM), 1,9-dideoxyforskolin (100 microM) and 4-OH tamoxifen (10 microM). Inclusion of the catalytic subunit of protein kinase A in the pipette solution did not activate the volume-sensitive anion channel in non-swollen cells. Furthermore, addition of 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP) or forskolin failed to activate the channel in intact cells under perforated patch conditions. Addition of phorbol 12,13-dibutyrate (200 nM), either before or after cell swelling, also failed to affect channel activation. Our findings do not support the suggestion that the volume-sensitive anion channel in pancreatic beta-cells can be activated by protein kinase A. Furthermore, the beta-cell channel does not appear to be subject to regulation via protein kinase C. Experimental Physiology (2001) 86.2, 145-150.

Animals↗
PubMed2001

Fibrinogen and preclinical echocardiographic target organ damage: the strong heart study.

Relations of fibrinogen to preclinical target organ damage, such as left ventricular hypertrophy, systolic dysfunction, and increased arterial stiffness while accounting for traditional risk factors, are unknown in a population-based sample free of clinically overt coronary heart disease. Therefore, we studied clinical and echocardiographic characteristics of 2709 American Indians participating in the Strong Heart Study without symptomatic atherosclerosis. The study sample was divided into tertiles of fibrinogen (cut-points, 3.24 and 3.83 g/L). Mean age, body mass index, proportion of women, and prevalences of hypertension and diabetes increased from the first to third tertile of fibrinogen. After adjustment for covariates, systolic and pulse pressures did not significantly differ among tertiles of fibrinogen, whereas diastolic pressure was slightly lower in the third than in lower tertiles of fibrinogen. HDL cholesterol was lower and plasma creatinine and urinary albumin/creatinine ratio was higher in the third tertile of fibrinogen. Left ventricular mass index, pulse pressure/stroke index, an estimate of arterial stiffness, and cardiac index were higher and left ventricular systolic function and total peripheral resistance were lower in the third than in two lower tertiles of fibrinogen independent of major covariates. In multiple regression analyses, left ventricular mass and pulse pressure/stroke index were positively associated with, and stress-corrected midwall shortening negatively associated with fibrinogen, independent of major covariates. Participants with fibrinogen >3.83 g/L were more likely to have at least 1 preclinical cardiovascular abnormality such as left ventricular hypertrophy, elevated arterial stiffness, or systolic myocardial dysfunction independent of covariates including renal dysfunction (adjusted odds ratio, 1.38; P<0.001). Thus, in a population sample of adults without clinically overt coronary heart disease, elevated fibrinogen is an independent correlate of prognostically relevant cardiovascular target organ damage.

Arteries↗
PubMed2000

Glucose-sensitive conductances in rat pancreatic beta-cells: contribution to electrical activity.

The perforated patch technique was used to assess the relative contribution of K(ATP) channel activity, assessed from input conductance (G(input)), and volume-sensitive anion channel activity to the induction of electrical activity in single isolated rat pancreatic beta-cells by glucose, 2-ketoisocaproate and tolbutamide. In cells equilibrated in the absence of glucose, the membrane potential was -71 mV and G(input) 3.66 nS. Addition of 8 mM glucose resulted in depolarisation, electrical activity and a reduction in G(input), reflecting an inhibition of K(ATP) channels. Cells equilibrated in 4 mM glucose had a membrane potential of -59 mV and a G(input) of 0.88 nS. In this case, a rise in glucose concentration to 8-20 mM again resulted in depolarisation and electrical activity, but caused a small increase in G(input). 2-Ketoisocaproate also evoked electrical activity and an increase in G(input), whereas electrical activity elicited by addition of tolbutamide was accompanied by reduced G(input). Increasing the concentration of glucose from 4 to 8-20 mM generated a noisy inward current at -70 mV, reflecting activation of the volume-sensitive anion channel. The mean amplitude of this current was glucose-dependent within the range 4-20 mM. Addition of 2-ketoisocaproate or a 15% hypotonic solution elicited similar increases in inward current. In contrast, addition of tolbutamide failed to induce the inward current. It is concluded that K(ATP) channel activity is most sensitive to glucose within the range 0-4 mM. At higher glucose concentrations effective in generating electrical activity, activation of the volume-sensitive anion channel could contribute towards the nutrient-induced increase in G(input).

Animals↗
PubMed2000

Selective inhibition of glucose-stimulated beta-cell activity by an anion channel inhibitor.

4,4'-Dithiocyanatostilbene-2,2'-disulfonic acid (DIDS), an inhibitor of the volume-sensitive anion channel, was used to investigate the role of this channel in the stimulation of rat pancreatic beta-cells by glucose and by tolbutamide. Glucose-stimulated electrical activity in beta-cells was markedly and reversibly inhibited by DIDS. The increase in cytosolic [Ca2+] and stimulated insulin release evoked by glucose were also inhibited by DIDS. In contrast to its inhibitory effect on glucose-induced beta-cell activity, DIDS had no effect on electrical activity, the rise in [Ca2+]i or insulin release induced by tolbutamide. DIDS failed to increase beta-cell input conductance, an index of whole-cell K(ATP) channel activity, or the rate of efflux of 86Rb+ from perifused islets, a measure of net K+ permeability. Furthermore, DIDS had no effect on intracellular pH or on regulatory volume increase following exposure of cells to hypertonic solutions, indicating that the effects of DIDS were not the result of inhibition of Cl- transport systems. It is suggested that the DIDS-induced repolarization is caused by inactivation of the volume-sensitive anion channel. The stimulation of beta-cell electrical and secretory activity by glucose, but not tolbutamide, may therefore involve activation of the anion channel.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed2000

Is Helicobacter pylori eradication associated with gastroesophageal reflux disease?

OBJECTIVES: A recent report has suggested an association between Helicobacter pylori eradication and the development of gastroesophageal reflux disease (GERD). We therefore assessed the incidence of GERD among comparable patients having undergone successful versus failed H. pylori eradication in a controlled trial. We also compared the H. pylori strains in the subjects that developed GERD to those that did not. METHODS: Patients with a history of proven duodenal ulcer and H. pylori infection were randomised into a H. pylori eradication study. Patients subsequently underwent gastroscopy with gastric biopsies every 3 months for 1 yr. At each visit, the presence of GERD symptoms and endoscopic esophagitis were noted, and the incidence of these variables among patients in whom H. pylori eradication was successful was compared to those in whom it was not. In a subgroup, the presence of the cagA, cagE, and vacA genotypes and of cagA antibodies were determined. RESULTS: Of 98 patients randomized into this study, 11 dropped out before determination of H. pylori eradication, leaving 87 patients with analyzable results. H. pylori eradication was successful in 63 (72%). By the end of the follow-up period, patients with GERD symptoms or endoscopic esophagitis were more prevalent in the successful than in the failed eradication group (37% [95% CI: 25-50%] vs 13% [95% CI: 3-32%], p = 0.04, 95% CI for the difference: 6-42%), as were patients with GERD symptoms alone (29% [95% CI: 18-41%] vs 8% [95% CI: 1-27%], p = 0.04, 95% CI for the difference: 4-36%) or esophagitis alone (21% [95% CI: 12-33%] vs 4% [95% CI: 0-21%], p = 0.10, 95% CI for the difference: 4-29%, respectively). Multivariate analysis revealed no significant association between the incidence of symptoms or esophagitis and age, gender, Quetelet index, caffeine or alcohol intake, smoking, weight change, or the presence of a hiatus hernia. There were also no differences in the prevalence of H. pylori genotypes from patients who developed GERD as compared to those who did not. CONCLUSIONS: In this patient population, the incidence of new GERD-type symptoms or endoscopic esophagitis was greater in patients in whom successful eradication was achieved. This difference does not appear to be attributable to weight gain, habits, or specific H. pylori strains.

Adolescent↗
PubMed1999

Cell-attached recordings of the volume-sensitive anion channel in rat pancreatic beta-cells.

The cell-attached configuration of the patch-clamp technique was used to study the volume-sensitive anion conductance in isolated rat pancreatic beta-cells at the single-channel level. In unstimulated cells, current level was close to zero. Exposure of cells to a 33% hypotonic solution resulted in the generation of an inward current at 0 mV pipette potential. A similar inward current was elicited by a rise in glucose concentration or by addition of alpha-ketoisocaproate. In contrast, the sulphonylurea tolbutamide was ineffective. The inward current evoked by hypotonic solutions consisted of occasional discreet channel events interspersed with periods of current noise which could not be clearly resolved into unitary channel events. Stimulation with glucose resulted in a predominantly noisy pattern of current. With a reduced [Cl(-)] pipette solution, regular channel openings could be resolved in the presence of a stimulatory glucose concentration, with a calculated conductance of 215 pS. Channel activity could also be recorded in excised inside-out patches, though rapid 'rundown' occurred under such conditions. It is concluded that hypotonic solutions and glucose activate the volume-sensitive anion channel in the cell-attached configuration by increasing channel open probability. This generates an inward current in non-voltage-clamped cells. The channel showed complex kinetics which depended in part upon extracellular [Cl(-)].

Animals↗