Calcium Channel Blocking Agent Verapamil Research Articles

MP67-09 HIGH-THROUGHPUT AND NON-INVASIVE FUNCTIONAL DRUG SCREENING PLATFORM FOR DROSOPHILA MELANOGASTER MODELS OF NEPHROLITHIASIS

INTRODUCTION AND OBJECTIVES: An experimental study in rats was performed to evaluate the potential protective effects of a calcium channel blocking agent (Verapamil) on the ischemia induced oxidative stress related changes during hyperoxaluric phase. METHODS: A total of 32 rats have been included into the study program. Hyperoxaluria was induced by continuous administration of ethyleneglycol (EG) (0.75%). In addition to hyperoxaluria induction applied in Group1 animals in Groups 2 did receive a calcium channel blocking agent (verapamil) and animals in Group 3 consituted the control group. Histologic alterations of the kidneys including crystal formation were evaluated on days 1,7 and 28, respectively. In addition to the scavenger enzymes (catalase (CAT), superoxide dismutase (SOD), total glutathione (GSH)),malonil dialdehid (MDA) levels, (nitric oxide)NO levelsand the total antioxidant capacity (TAOC) of the kidney were also assessed both in the serum as well as the kidney tissue specimens of the animals in all groups. RESULTS: While the evlautaion of the antioxidant enzyme levels did reveal a significant reduction in animals receiving EG only; application of verapamil was found to be protective with limited reduction with a statistical significance when compared with the control group animals (Sidak-Bonferroni method, alpha1⁄41.000%). Moreover, comparison of kidney tissue T-AOC as well as NO levels in a comparative manner between the groups agan showed a statistically significant difefrence between Group 1 and the other group animals where the antioxidant capacity of the kidney seemed to be protected by verapamil application (Sidak-Bonferroni method, alpha1⁄4 1.000%). Lastly, both serum as well as tissue MDA levels were also statistically significant high in animals receiving EG only when compared with Group 2 and control animals during day7 as well as day 28 evaluation. CONCLUSIONS: Our current results indicate that as a potent calcium channel blocking agent Verapamil may limit the extent of oxidative stress related changes in renal tubules following hyperoxaluria induction and preservation of antioxidant capacity of the kidney along with the limitation of crystallization by this agent may allow us to understand the pathophysiology of stone formation as well as the possible use of this agent to limit both stone formation and recurrence.

Effects of Arsenic Trioxide on Protein Kinase C and Cytosolic Calcium in Ventriclar Myocardium of Guinea Pig.

AIM To clarify the mechanisms of the cardiac side effects of arsenic trioxide (As2O3) in leukemia treatment, the effects of As2O3 on protein kinase C(PKC) and cytosolic calcium ([Ca2+]i) in ventriclar myocardium of guinea pig were investigated.METHODS Fluo-3/AM fluorescent probe tagged [Ca2+]i of guinea pig's ventriclar myocardium, detected the [Ca2+]i, by laser confocal microscopy before and after exposed to As2O3. Phosphorus radioisotope assay was used to detect the activity of PKC on cell membrane or in cytoplasm. DNA ladders of ventriclar myocardium in Tyrode's solution after exposed to As2O3 were evaluated.RESULTS The cytosolic [Ca2+]i did not change when incubated guinea pig's ventriclar myocardium in Tyrode's solution with 0.5μmol•L−1As2O3, after incubated in2μmol•L−1As2O3 for 6min, [Ca2+]i began to increase and was continuous increasing for about 9min. After exposed to 10μmol•L−1As2O3 for less than 3 min, the [Ca2+]i kept on increasing till the end (about 27min) of the examination and could not recover. The increasing of [Ca2+]i could be partly blocked by calcium channel blocking agents—verapamil and nifedipin. The PKC of myocardial cells began to rise after incubated in an As2O3 changing concentration culture media for 3 hours, which initial As2O3 was 10μmol•L−1, and the DNA ladders appeared after incubated in it for10 hours. No DNA ladders appeared when incubated in an As2O3 culture media in which the initial As2O3 concentration was under 5μmol•L−1.CONCLUSIONS As2O3 can active PKC, increase cytosolic [Ca2+]i and promote apoptosis of myocardial cells. The promoting apoptosis action of As2O3 is closely related to the lasting activation of PKC. The initial action target of As2O3 is cell membrane.

Regulation of free arachidonic acid levels in isolated salivary glands from the lone star tick: a role for dopamine.

An important regulatory step for prostaglandin synthesis is the availability of the precursor, free arachidonic acid (AA). In isolated salivary glands of the lone star tick, Amblyomma americanum (L.), the level of free AA appears to depend on higher phospholipase A2 (PLA2) activity rather than decreased rates of re-esterification by lysophosphatide acyl transferase (LAT). This conclusion is supported by experiments where inhibition of LAT with merthiolate was without effect, while the calcium ionophore A23187, a PLA2 stimulant, increased levels of free AA. The PLA2 activity in A. americanum was reduced by the substrate analog, PLA2 inhibitor, oleyloxyethyl phosphorylcholine in a dose-dependent manner, but was insensitive to the other mammalian PLA2 inhibitors mepacrine (20 microM), aristolochic acid (45 microM), and dexamethasone (50 microM). No substrate preference was observed for the functional group of the phospholipid, with phosphatidylcholine and phosphatidylethanolamine being equal sources of AA in A23187-stimulated glands. Compared to phospholipids containing other fatty acids, only arachidonyl-phospholipid (arachidonyl-PL) was significantly hydrolyzed by PLA2 activity in A23187-stimulated glands. Dopamine was as effective as A23187 as a stimulant of PLA2 activity in isolated glands, but this effect was abolished in the presence of the calcium channel blocking agent verapamil. It is concluded that free AA levels in tick salivary glands are increased through activation of a Type IV-like PLA2 following an increase of intracellular calcium caused by the opening of voltage-dependent calcium channels due to dopamine stimulation.

PTH stimulates the proliferation of TE-85 human osteosarcoma cells by a mechanism not involving either increased cAMP or increased secretion of IGF-I, IGF-II or TGFβ

Injections of parathyroid hormone (PTH) result in increased bone formation in several species. Work in our laboratory and others has shown a stimulation of bone cell proliferation and growth factor production by PTH. Our purpose was to study the effects of PTH on a human bone cell line using TE-85 human osteosarcoma cells as a model. After 24 h treatment, PTH caused an increase in cell proliferation as measured by cell counts and [ 3H]-thymidine incorporation. Proliferation was not inhibited by an anti-transforming growth factor beta (TGFβ) antibody which could abolish stimulation by exogenous TGFβ. PTH did not stimulate cAMP production, alkaline phosphatase activity or production of insulin-like growth factors I or II (IGF-I or IGF-II) in TE-85 cells. Although basal TE-85 proliferation was slowed by incubation with the calcium channel blocking agent verapamil, PTH still caused an increase in growth rate. We conclude that PTH directly stimulates TE-85 proliferation via a mechanism not involving increased adenylate cyclase activity or increased secretion of IGF-I, IGF-II or TGFβ and may stimulate bone formation in vivo by activating some other mitogenic signal to increase bone cell proliferation.

CALCIUM-CHANNEL BLOCKING AGENTS VERAPAMIL AND DILTIAZEM ARE INHIBITORS OF VASOPRESSIN-INDUCED HUMAN PLATELET ACTIVATION

1. This study investigated the influences of calcium-channel blocking agents verapamil and diltiazem on platelet responses induced by arginine vasopressin (AVP) and lysine vasopressin (LVP). 2. The substances inhibited platelet aggregation induced by both low and high AVP concentrations, LVP and adrenaline plus AVP. IC50 values of each drug are lower than those determined for ADP- and collagen-elicited aggregation. Verapamil and diltiazem also decreased AVP-induced thromboxane B2 synthesis. 3. Other series of experiments showed that the addition of ethyleneglycol-bis-(beta-amino-ethyl ether) N, N'-tetra-acetic acid to platelet-rich plasma samples also prevented the platelet response to vasopressin polypeptides. 4. Our data provide evidence that the effects of verapamil and diltiazem on vasopressin-induced platelet responses may be directly related to inhibition of extracellular calcium entry.

The Calcium Messenger System and the Kinetics of Elastase Release from Human Neutrophils in Patients with Abdominal Aortic Aneurysms

Aortic elastase and neutrophil elastase is higher in patients with abdominal aortic aneurysms. The purpose of this study was to determine if these proteolytic elevations occur after abdominal aortic aneurysms have been repaired. Specifically, we studied the stimulation and inhibition of elastase degranulation from neutrophils in postoperative abdominal aortic aneurysm patients compared to aortic occlusive disease patients. Neutrophil elastase was determined in postoperative abdominal aortic aneurysm and aortic occlusive disease patients in response to calcium and the ionophore A23187. Inhibition of elastase release was determined with the calcium channel blocking agent Verapamil. Neutrophil elastase secretion was significantly higher in the abdominal aortic aneurysm patients (47%) versus aortic occlusive disease (20%) (p less than .05), while the effect of Verapamil in blocking this response was significantly lower in the abdominal aortic aneurysm patients (14%) compared to aortic occlusive disease patients (27%) (p less than .02). The time for degranulation to occur was longer in the abdominal aortic aneurysm patients (14.7 minutes) versus aortic occlusive disease patients (3.5 minutes), but the rate of secretion was not different between the two groups. These data indicate that, (1) neutrophils secrete more elastase in response to a calcium stimulus in abdominal aortic aneurysm patients; (2) it takes longer to secrete the increased amount of elastase in abdominal aortic aneurysm patients since the rate of secretion is similar between the two groups; and (3) Verapamil blocks elastase secretion ineffectively in abdominal aortic aneurysm patients. We conclude that the proteolytic alterations in abdominal aortic aneurysm patients are more likely a primary event and not a response to the abdominal aortic aneurysm and that Verapamil is a poor drug to use to medically manipulate the protease system in abdominal aortic aneurysm patients.

Metabolic protection by verapamil during graded coronary flow reduction independent of effect on baseline systolic function. Separation of mechanical and ionic markers of ischemia.

Pretreatment with the calcium channel-blocking agent verapamil lowers the coronary flow associated with the first rise in myocardial extracellular potassium [( K+]e). The mechanisms underlying this effect are unclear. It is not known whether this effect is a manifestation of verapamil-induced reduction in baseline cardiac work before the reduction in coronary flow, is dependent on a selective depression of contractility within the low-flow region, or is independent of an effect on myocardial work. This study was performed to determine the relations between changes in regional contractility and [K+]e before and after verapamil (0.2 mg/kg followed by 6.5 micrograms/kg/min) when left anterior descending (LAD) coronary flow is progressively reduced and when verapamil-induced alterations in baseline myocardial work are prevented by atrial pacing and by dobutamine (4.3 +/- 2.2 micrograms/kg/min) to maintain systemic arterial blood pressure and contractility. Before verapamil-dobutamine, myocardial [K+]e rose and regional contractility fell when LAD coronary flow was reduced to 87.7 +/- 9.6% and 83.4 +/- 7.4%, respectively, of the unrestricted control value (p = NS). After verapamil-dobutamine, the threshold flow for rise in [K+]e decreased to 56.4 +/- 13.5% of the unrestricted control flow (p = 0.003), but the threshold flow for regional contractility fall was unchanged (84.8 +/- 11.3%). Our results indicate that the protective effect of verapamil on preventing ischemia-induced [K+]e release is not dependent on a reduction in baseline myocardial work. In this setting, calcium channel blockade by verapamil results in a dissociation between the ionic and mechanical events that occur when coronary flow is reduced.

Effects of calcium availability on the release of ovine choriomammotropin from cotyledonary cells incubated in vitro

1. 1. In this study, we examined the basal release of choriomammotropin (oCM) from monolayer cultures of cotyledonary cells obtained from ewes at different gestational ages. 2. 2. oCM release increased with gestational age and displayed a similar profile to the concentration of oCM observed in maternal plasma. 3. 3. Release of oCM was significantly ( P < 0.05; n = 9) increased in calcium-depleted medium, and by treatment with either phospholipase C (0.125 units/ml) or KCl (50 mM). 4. 4. The calcium antagonist MgCl (12mM) and the calcium channel-blocking agents verapamil (50 μM) and nefidipine (10 μM) all significantly stimulated oCM release. 5. 5. These data are consistent with the suggestion that oCM release is inversely related to extracellular calcium concentration.

Modulation of mitoxantrone cytotoxicity by verapamil in human chronic myeloid leukemia cells.

Calcium channel-blocking agent verapamil has been established to be an effective drug to modulate the action of many anticancer drugs. In this study, we examined the effect of verapamil on the cytotoxicity of mitoxantrone in human chronic myeloid leukemia (CML) cells. Mitoxantrone alone exhibited dose-dependent inhibition of DNA biosynthesis in CML cells. The addition of verapamil (3.3 microM) enhanced the responsiveness of CML cells to mitoxantrone (1 microgram/ml) cytotoxicity indicated by significant increased inhibition of thymidine incorporation (p less than 0.001). The present study demonstrates the possible efficacy of verapamil in the chemotherapy of CML with mitoxantrone.

Effects of verapamil and converting enzyme inhibition on bilateral renal function of two-kidney, one-clip hypertensive rats.

Experiments were conducted in two-kidney, one-clip renal vascular hypertensive rats (GHR) to assess the responses of each kidney to acute treatment with the antihypertensive calcium channel blocking agent verapamil in the presence and in the absence of converting enzyme inhibitor (CEI). One group of GHR (0.2 mm inner diam. clip 3 weeks before study) were examined during a control period, and during a second period of infusion of verapamil (600 micrograms h-1 kg-1). A second group of GHR were examined during a control period, during CEI (teprotide, 3 mg h-1 kg-1) infusion and during a third period of verapamil (600 micrograms h-1 kg-1) infusion superimposed on CEI infusion. Although systemic blood pressure (BP) decreased from 175 +/- 4 to 149 +/- 5 mmHg (mean +/- SEM) in response to verapamil alone, renal blood flow for non-clipped kidneys increased from 5.9 +/- 0.4 to 6.5 +/- 0.3 ml/min, indicating a 30% reduction of renal vascular resistance (P values less than or equal to 0.01; n = 9). Glomerular filtration rate (GFR) for non-clipped kidneys (n = 24) increased from 0.91 +/- 0.09 to 1.47 +/- 0.14 ml/min and filtration fraction increased from 0.32 +/- 0.04 to 0.47 +/- 0.03 (P values less than or equal to 0.05). Urine flow rate and absolute and fractional sodium excretion for non-clipped kidneys increased. GFR for clipped kidneys decreased during verapamil. Treatment with CEI alone resulted in nearly identical responses of BP and function of the non-clipped kidney, except filtration fraction was unchanged. The addition of verapamil to ongoing converting enzyme blockade tended to augment the increased GFR of the non-clipped kidney. Plasma renin activity (PRA) increased from 30 +/- 3 to 59 +/- 7 ng of angiotensin (ANG) I h-1 ml-1 with verapamil alone, a significantly larger increment than the increase of PRA from 27 +/- 5 to 39 +/- 9 ng of ANG I h-1 ml-1 in GHR subjected to comparable blood pressure reduction by mechanical aortic constriction. Verapamil resulted in many similar effects on renal function to those observed during blockade of converting enzyme. The increased filtration fraction observed in response to verapamil may be the result of vasodilatation of the afferent arteriole or of an increase in the glomerular ultrafiltration coefficient.

ABNORMAL MEMBRANE DEPOLARIZATION IN THE PATHOGENESIS OF THE CHEMOTACTIC DEFECT IN NEONATAL PMNS

Although a number of investigators have reported that neonatal PMNs have a profound defect in chemotaxis, almost nothing is known about the pathogenesis of this disorder. In the present study we have examined membrane depolarization and calcium requirements for chemotaxis in neonatal and adult PMNs. Suspension of adult PMNs in calcium deprived media resulted in a decreased chemotactic response to FMLP (19% inhibition; p<0.05). Incubation of adult PMNs with the calcium channel blocking agent verapamil also significantly impaired chemotaxis (32% inhibition p<0.001). In marked contrast, the neonatal PMN demonstrated an enhanced chemotactic response when suspended in calcium deprived media (26% increase; p<0.05) and after incubation with verapamil (57% increase; p<0.001), suggesting that inhibitory levels of intracellular calcium might already exist. Adult and cord blood PMN membrane potential changes in response to FMLP were also studied using the membrane potential-sensitive dye, 3-3' dipenty-loxacarbocyanine and a spectrofluorescence assay. Adult PMNs showed a marked increase in fluorescence emission in response to FMLP (32% increase; p<0.001) indicating significant depolarization of the cell membrane. In contrast, FMLP stimulation of neonatal PMNS failed to evoke any significant change in fluorescence and, thus, membrane potential changes. These data suggest that altered intracellular calcium metabolism may exist in the neonatal PMN, preventing normal membrane depolarization from occurring.

Effects of verapamil on contraction and relaxation of cultured chick embryo ventricular cells during calcium overload

The calcium channel blocking agents verapamil and nifedipine have been reported to lessen abnormalities of left ventricular relaxation in patients with severe left ventricular hypertrophy or coronary artery disease. Whether these effects in human beings are related in part to a direct effect on myocardial calcium metabolism is difficult to determine because of complicating drug influences on ventricular loading via systemic arterial vasodilation, on myocardial blood supply via coronary artery vasodilation and on reflex changes in sympathetic tone. For this reason, the effects of verapamil were investigated in a cellular model of impaired relaxation using spontaneously contracting tissue cultured monolayers of chick embryo ventricular cells exposed to high external calcium ([Ca]o). Under control conditions ([Ca]o, 0.9 mM), verapamil (2 X 10(-8)M) induced a 57 +/- 8% decrease in amplitude of cell contraction monitored with a phase contrast microscope video motion detector system. Elevation of [Ca]o from 0.9 to 8.0 mM resulted in a decrease in amplitude and velocity of contraction and a decrease in velocity of relaxation associated with an upward shift in diastolic cell wall position, suggesting a failure of normal myofilament dissociation. These abnormalities were completely reversible on reperfusion with [Ca]o, 0.9 mM. On re-exposure of the cells to [Ca]o, 8.0 mM, in the presence of verapamil, there was an increase in amplitude of contraction (0.56 +/- 0.11 to 1.03 +/- 0.09 micron, p less than 0.01) and velocity of relaxation (4.97 +/- 0.89 to 9.94 +/- 0.87 micron/s, p less than 0.01) compared with exposure to [Ca]o, 8.0 mM, alone, and an attenuation of the upward shift in diastolic cell wall position.(ABSTRACT TRUNCATED AT 250 WORDS)

Fibrinogen interaction with human platelets: Effect of other coagulation factors, prostaglandins and platelet inhibitors

Fibrinogen (fg) binding to platelets is a critical step in the formation of the hemostatic plug. The interaction requires platelet stimulation and the induction of receptor sites on the platelet membrane. In this paper we report on the effect of other clotting factors on 125I-labeled fg binding to gel filtered human platelets. The action of exogenously added or endogenously synthesized prostaglandins and the effect of antiplatelet drugs were also investigated. Prothrombin and active factor X enhance ADP-induced platelet-fg binding whereas active factor VIII and active factor IX, separately or combined, are without effect. Human prothrombin complex (PC) factor concentrates (II-VII-IX-X) cause significant enhancement of platelets-fg binding; this effect is most likely due to activated factors and/or traces of thrombin present in the preparation. In the concentration used, these clotting factors and the PC factor concentrates failed to aggregate platelets in platelet rich plasma. Acetylsalicylic acid, carbenicillin and the calcium channel blocking agents verapamil and nifedipine showed variable degrees of inhibition of ADP-induced platelet-fg binding. Chlorpromazine and propranolol were without effect. Estrogen and progesterone had some enhancing effect on binding. These results suggest that, when the hemostatic mechanism is initiated, thromboxane A 2 synthesis and activated prothrombin complex factors significantly enhance fg binding to platelets, a key step in hemostasis. Inhibitors of aggregation do not necessarily impede platelet fibrinogen interaction.

Verapamil therapy for stable exertional angina pectoris

Clinical and exercise responses to therapy with the calcium-channel blocking agent verapamil were assessed in 26 patients with stable exertional angina pectoris using a double-blind, placebo-controlled, randomized crossover study design. Verapamil, 480 mg daily, reduced the frequency of angina attacks (5.6 ± 7.3 to 2.2 ± 3.0 attacks per week, p <0.001) and number of nitroglycerln tablets consumed (3.4 ± 4.9 to 1.2 ± 2.5 tablets per week, p <0.05), and increased exercise duration (6.4 ± 2.1 to 7.5 to 1.8 minutes, p <0.001) (all data are mean ± standard deviation). These changes were significantly better than those seen with placebo. These beneficial effects of verapamil were related to significant reduction in the heart rate-systolic blood pressure product during submaximal exercise. Adverse effects from verapamil were few and consisted primarily of constipation in 6 patients. A total of 193 patients had been entered in 6 independent clinical trials, which have compared verapamil with placebo for the treatment of stable exertional angina pectoris, using a similar study design. The combined evidence from all these studies indicates that verapamil is a highly effective and safe drug for the treatment of stable effort-related angina pectoris.

The effect of verapamil on myocardial ultrastructure during and following release of coronary artery occlusion

Although the calcium channel blocking agent verapamil has been shown to have beneficial effects on ischemic myocardium, its effect on cardiac ultrastructure during regional myocardial ischemia and following coronary reperfusion has not been studied in detail. The purpose of this study was to investigate the effect of verapamil on the ultrastructure of myocardium during the early phase of ischemia and following coronary reperfusion. Open-chest anesthetized dogs were subjected to 1 hr of occlusion of the proximal left anterior descending coronary artery followed by 1 hr of reperfusion. The mean ischemic score, a semiquantitative index of ultrastructural damage, was significantly lower in verapamil-treated (0.9 ± 0.3) than in untreated dogs (1.9 ± 0.2, P < 0.025) during coronary occlusion and especially following reperfusion (1.0 ± 0.3 versus 2.9 ± 0.5, respectively P < 0.025). Verapamil treatment prevented the hastening of ultrastructural damage (explosive cell swelling phenomenon) associated with reperfusion into severely ischemic myocardium. Verapamil resulted in a more profound reduction of the extent of ultrastructural damage of mitochondria compared to other organelles. Thus, this study supports the concepts that verapamil reduces ultrastructural damage both during coronary occlusion and following coronary reperfusion and may reduce ischemic damage by protecting mitochondrial structure.

Antiarrhythmic and hemodynamic effects of calcium channel blocking agents during coronary arterial reperfusion: Comparative effects of verapamil and nifedipine

To determine the comparative actions of the calcium channel blocking agents verapamil and nifedipine on coronary flow and ventricular arrhythmias during myocardial reperfusion, 24 open chest dogs underwent proximal occlusion of the left anterior descending coronary artery. Regional myocardial blood flow (ml/mln per 100 g) was quantltated by microspheres (strontium [ 85Sr]and cerium [ 141Ce]) 20 minutes after coronary occlusion and 10 minutes after reperfusion. Dogs were randomly assigned to one of three groups 20 minutes after coronary occlusion: (1) control group ( n = 8); (2) dogs given intravenous verapamil ( n = 8), 0.2 mg/kg body weight in 5 minutes followed by an infusion of 0.01 mg/kg per min; or (3) dogs given nifedipine ( n = 8), 100 μg/kg in 5 minutes followed by an infusion of 3 μg/kg per min. Ten minutes after reperfusion, transmural regional myocardial blood flow in the ischemic zone was unchanged by verapamil and nifedipine (p = not significant [NS]versus control value). The endocardial/epicardial ratio in the hyperemlc zone tended to be lowered by the calcium blocking agents compared with that observed in control animals. Coronary resistance during reperfusion was similar ( p = NS) in animals treated with verapamil and nifedipine. Ventricular tachycardia or fibrillation occurred in six dogs In the control group (tachycardia in three and fibrillation in three). Among dogs given verapamil, none had ventricular tachycardia and one of eight had ventricular fibrillation ( p <0.05 versus control value). Four of the eight dogs given nifedipine, had ventricular tachycardia (two dogs) or fibrillation (two dogs) ( p = NS versus control and verapamil values). Thus, verapamil and nifedipine had similar effects on central and coronary hemodynamics during myocardial reperfusion. However, verapamil, in contrast to nifedipine, decreased reperfusion ventricular arrhythmias. These data suggest that despite similar calcium channel blocking actions, verapamil and nifedipine possess different antiarrhythmic effects.

Circumcision

A preterm female infant presented with intractable hypoglycaemia within 10 minutes of delivery. Normoglycaemia could be maintained only by the intravenous infusion of glucose at a rate of 20-22 mg/kg/min. Persistent hyperinsulinaemic hypoglycaemia of infancy was diagnosed from an inappropriately raised plasma insulin concentration (33 mU/l) at the time of hypoglycaemia (blood glucose &lt; 0.5 mmol/l). Medical treatment with glucagon, somatostatin, and diazoxide led to only a modest reduction in the intravenous glucose requirement; a 95% pancreatectomy was performed and histological 9nesidioblastosis9 confirmed. In vitro electrophysiological studies using patch clamp techniques on isolated pancreatic beta cells characterised the ionic basis for insulin secretion in nesidioblastosis. The beta cells were depolarised in low ambient glucose concentrations with persistently firing action potentials; these were blocked reversibly by the calcium channel blocking agent verapamil. Persistent postoperative hyperinsulinaemic hypoglycaemia was treated with oral nifedipine. This increased median blood glucose concentrations from 3.5 to 4.8 mmol/l and increased in duration the child9s tolerance to fasting from 3 to 10.5 hours. These data allude to an abnormality in the ionic control of insulin release in nesidioblastosis and offer a new logical approach to treatment which requires further evaluation.