Opposite effects of tolbutamide and diazoxide on the ATP-dependent K+ channel in mouse pancreatic ?-cells

Abstract

The influence of the antidiabetic sulphonylurea tolbutamide on K+ channels of mouse pancreatic beta-cells was investigated using different configurations of the patch clamp technique. The dominant channel in resting cells is a K+ channel with a single-channel conductance of 60 pS that is inhibited by intracellular ATP or, in intact cells, by stimulation with glucose. In isolated patches of beta-cells membrane, this channel was blocked by tolbutamide (0.1 mM) when applied to either the intracellular or extracellular side of the membrane. The dose-dependence of the tolbutamide-induced block was obtained from whole-cell experiments and revealed that 50% inhibition was attained at approximately 7 microM. In cell-attached patches low concentrations of glucose augmented the action of tolbutamide. Thus, the simultaneous presence of 5 mM glucose and 0.1 mM tolbutamide abolished channel activity and induced action potentials. These were not produced when either of these substances was added alone at these concentrations. The inhibitory action of tolbutamide or glucose on the K+ channel was counteracted by the hyperglycaemic sulphonamide diazoxide (0.4 mM). Tolbutamide (1 mM) did not affect Ca2+-dependent K+ channels. It is concluded that the hypo- and hyperglycaemic properties of tolbutamide and diazoxide reflect their ability to induce the closure or opening, respectively, of ATP-regulated K+ channels.

Inhibition of electrical activity in mouse pancreatic β‐cells by the ATP/ADP translocase inhibitor, bongkrekic acid

“…[ 11rnM Glucose ductance of 57 := 0.6 pS (n = 3) and a reversal potential of -74 ± 5.2 mV (n = 5), properties consistent with those of the glucose.sensitive channel (K-ATP-channel) that are well described in ~-cells [5,[11][12][13]. Addition of 11 mM glucose produced a gradual reduction in both channel activity and the single-channel current amplitude.…”

“…lO EGTA, 10 KOH.HEPES, I CaCl= (pH ?,2). 0,3 mM Na=ATP was included in the pipette solution to reduce rundown of K-ATP-channels [12]. Currents were recorded using a List EPC.7 amplifier (List, Darmstadt, Germany), filtered at ()..~ kHz (8-pole Bessel; Frequency Devices) and were digltised at l kHz (PCLAMP, Axon Instruments, Burlingame, USA), They were analysed using PCLAMP software.…”

“…The effects of bongkrekic acid on K.ATP-channels were studied in cell-attached membrane patches [12]. Fig.…”

Mechanisms of Exocytosis in Insulin‐Secreting B‐Cells and Glucagon‐Secreting A‐Cells

“…The principal effect of the sulfonylureas is to stimulate insulin secretion from the B-cells (Ashcroft & Ashcroft 1992). This is a consequence of their ability to selectively inhibit the K ATPchannels in the B-cell plasma membrane (Trube et al 1986) by binding to its sulfonylurea receptor (Aguilar-Bryan et al 1995) subunit. This short-circuits the normal physiological regulation of the channel by the metabolic state of the cell (via the ATP/ADP-ratio) and results in membrane depolarization, Ca 2π -influx and insulin secretion (Ashcroft & Rorsman 1989).…”

Effect of atrial natriuretic factor (ANF) on nicotinic acetylcholine receptor channels in bovine chromaffin cells

“…Based on this scheme, we have fitted a theoretical curve to the data, as has been reported elsewhere to describe the block of ion channels by drugs (Trube et al 1986;OhnoShosaku et al 1987):…”