Nucleotide Regulation of a calcium-activated cation channel in the rat insulinoma cell line, CRI-G1.

The nucleotide regulation of a calcium-activated nonselective cation (Ca-NS+) channel has been investigated in the rat insulinoma cell line CRI-G1. The activity of the channel is reduced by both AMP and ADP (1-100 microM) in a concentration-dependent manner, with AMP being more potent than ADP. At lower concentrations (0.

The effects of trypsin on ATP-sensitive potassium channel properties and sulfonylurea receptors in the CRI-G1 insulin-secreting cell line.

The effects of the proteolytic enzyme trypsin upon ATP-sensitive potassium (KATP) channel activity were examined in the CRI-G1 insulin-secreting cell line. Trypsin activated channels only when applied to the intracellular surface of the cell membrane. The activation could be prevented by the concomitant application of trypsin inhibitor or by heat inactivation of the enzyme.

Effects of chemical modification of amino and sulfhydryl groups on KATP channel function and sulfonylurea binding in CRI-G1 insulin-secreting cells.

The effects of several group-specific chemical reagents were examined upon the activity of the ATP-sensitive potassium (KATP) channel in the CRI-G1 insulin-secreting cell line. Agents which interact with the sulfhydryl moiety (including 1 mM N-ethyl-maleimide (NEM), 1 mM 5,5'-dithio-bis-(2-nitrobenzoic acid) (DNTB) and 1 mM o-iodobenzoate) produced an irreversible inhibition of KATP channel activity when applied to the intracellular surface of excised inside-out patches. This inhibition was substantially reduced when attempts were made to eliminate Mg2+ from the intracellular compartment.

Mg(2+)-dependent inhibition of KATP by sulphonylureas in CRI-G1 insulin-secreting cells.

1 Patch-clamp recording techniques were used to examine the effects of tolbutamide, glibenclamide, meglitinide and thiopentone on KATP in CRI-GI insulin-secreting cells in the presence and absence of Mg2+. 2 In the absence of Mg2+ in the intracellular bathing solution, tolbutamide was significantly less effective when applied either to the intracellular or to the extracellular surfaces of cell-free patches. Removal of extracellular Mg2+ did not alter the effectiveness of tolbutamide provided that Mg2+ was present at the intracellular surface of the patch.

Targeting drugs to the colon: delivery systems for oral administration.

The oral delivery of drugs to the colon has applications in a variety of therapeutic areas. This review is concerned with the approaches taken to achieve a universal system for delivery. The design of such a system requires the identification and exploitation of a unique feature of the colonic environment.

Mg2+ modulates the binding of [3H]glibenclamide to its receptor in rat cerebral cortical membranes.

Radioligand binding studies were performed to determine the effect of various cations on the characteristics of [3H]glibenclamide binding to its high-affinity receptor in rat cerebral cortex membranes. Mg2+ was shown specifically to reduce radioligand binding to membranes pretreated with 5 mM EDTA. CaCl2 enhanced [3H]glibenclamide binding whilst MnCl2, KCl and NaCl were without significant effect.

The effects of potassium channel openers on isolated pregnant human myometrium before and after the onset of labor: potential for tocolysis.

Objective: Our purpose was to investigate the effects and pharmacologic properties of potassium channel openers in isolated pregnant human myometrium.

Study Design: Biopsy specimens of myometrium obtained from 67 women during pregnancy and labor were used for isometric recording under physiologic conditions.

Results: Levcromakalim and pinacidil, two prototype potassium channel openers, are potent inhibitors of spontaneous and induced (0.

Dissociation of KATP channel and sulphonylurea receptor in the rat clonal insulin-secreting cell line, CRI-D11.

It is generally considered that the sulphonylurea receptor is an integral part of the ATP-sensitive K+ channel. We have investigated this proposal by comparing the binding and functional characteristics of the sulphonylurea receptor and KATP channel by using two rat insulinoma cell lines (CRI-G1 and CRI-D11) of common origin. Insulin release was increased in both cell lines by a variety of metabolizable and non-metabolizable secretagogues but glibenclamide induced an increase in insulin release in G1 cells only.

Properties of large-conductance K+ channels in human myometrium during pregnancy and labour.

The conversion of the electrically silent pregnant uterus to highly excitable at term represents a dramatic physiological event which is poorly understood. Here we provide the first description, from single-channel recordings, of a large conductance (212 pS) calcium-activated potassium channel (BKCa) in human pregnant myometrium which, in labour tissue, is either absent or has been considerably altered in its physiological and pharmacological properties. In the latter, the K+ channels have an identical conductance (221 pS) and K+ selectivity to BKCa channels but exhibit no Ca2+ or voltage sensitivity.

Lack of effect of potassium channel openers on ATP-modulated potassium channels recorded from rat ventromedial hypothalamic neurones.

1. Single neuronal cells were freshly isolated from the ventromedial hypothalamic nuclei (VMHN) of the rat brain. Currents through ATP-modulated and large conductance (160 and 250 pS) calcium-activated potassium channels were recorded by the cell-attached and excised inside-out patch techniques.

Nucleotide-dependent activation of KATP channels by diazoxide in CRI-G1 insulin-secreting cells.

1. Patch-clamp recording techniques were used, to examine the effects of diazoxide on KATP currents in CRI-G1 insulin-secreting cells in the presence of non-hydrolysable nucleotides. 2.

Chloride channels and anion fluxes in a human colonic epithelium (HCA-7).

1. Colonic epithelial cells, derived from a human adenocarcinoma (HCA-7), were examined by the patch clamp technique. 2.

Extracellular cations modulate the ATP sensitivity of ATP-K+ channels in rat ventromedial hypothalamic neurons.

ATP-sensitive K+ (ATP-K+) channels underlie the glucose-sensing nature of pancreatic beta-cells by way of their inhibition by intracellular ATP. Recently it has been proposed that ATP-K+ channels have a similar function in certain hypothalamic neurons that become excitable in raised concentrations of extracellular glucose. The aim of this study was to assess the ATP sensitivity of ATP-K+ channels in inside-out membrane patches excised from glucose-sensing neurons that were acutely isolated from the ventromedial nucleus of rat hypothalamus.

Characterization of sulfonylurea receptors and the action of potassium channel openers on cholinergic neurotransmission in guinea pig isolated small intestine.

Specific binding sites for [3H]glibenclamide, a potent ATP-sensitive K+ channel blocker, have been characterized in the isolated guinea pig longitudinal muscle-myenteric plexus preparation. The Scatchard plot of the saturation isotherm was curvilinear and revealed two binding sites, one of high affinity (Kd = 0.42 nM; maximum binding site = 156 fmol/mg of protein), the other of low affinity (Kd = 83 nM; maximum binding site = 3100 fmol/mg of protein).

Barbiturates inhibit ATP-K+ channels and voltage-activated currents in CRI-G1 insulin-secreting cells.

1. Patch-clamp recording techniques were used to examine the effects of barbiturates upon the ATP-K+ channel, and voltage-activated channels present in the plasma membrane of CRI-G1 insulin-secreting cells. 2.

Calcium-activated potassium channels in rat dissociated ventromedial hypothalamic neurons.

Abstract A potassium-selective channel, characterized by a single channel conductance of 160 pS was demonstrated to be present in rat freshly dispersed ventromedial hypothalamic nucleus neurons. The single channel activity was shown to be dependent, using inside-out membrane patches, upon the presence of intracellular calcium ions, with maximal sensitivity between 10(-6) and 10(-6) M[Ca(2+)], and to be modulated by membrane voltage, depolarization causing an increase in open-state probability in the presence of an activating concentration of calcium. Therefore these properties place this channel into the category of a large conductance (maxi-K(+)) calcium-activated potassium (Ca(2+)-K(+)) channel.

The regional distribution of sulphonylurea binding sites in rat brain.

Sulphonylureas such as glibenclamide, which are used in the treatment of Type-2 diabetes, are inhibitors of ATP-sensitive potassium channels. These channels link cellular metabolism to membrane electrical activity and it is likely that they are closely associated with glibenclamide binding sites. Quantitative autoradiography was used to localize high-affinity [3H]glibenclamide binding sites in coronal sections of rat brain.

Voltage-activated currents in the CRI-G1 rat insulin-secreting cell-line.

1. The whole-cell configuration of the patch-clamp recording technique was used to characterize the electrophysiological properties of CRI-G1 insulin-secreting cells. 2.

Tolbutamide excites rat glucoreceptive ventromedial hypothalamic neurones by indirect inhibition of ATP-K+ channels.

1. The sulphonylureas, tolbutamide (0.1-10 mM) and glibenclamide (0.

ATP-sensitive K(+)-channel run-down is Mg2+ dependent.

ATP-sensitive K(+)-channel currents were recorded from isolated membrane patches and voltage-clamped CRI-G1 insulin-secreting cells. Internal Mg2+ ions inhibited ATP-K+ channels by a voltage-dependent block of the channel current and decrease of open-state probability. The run-down of ATP-K+ channel activity was also shown to be [Mg2+]i dependent, being almost abolished in Mg2(+)-free conditions.

Glucose-induced excitation of hypothalamic neurones is mediated by ATP-sensitive K+ channels.

Intracellular recordings were made from neurones located in the ventromedial hypothalamic nucleus (VMHN) of slices from rat hypothalamus. These neurones were hyperpolarized on removal of extracellular glucose, resulting in an inhibition of firing, actions which were reversed on the re-introduction of glucose. No reversal of the inhibition of firing was observed when 10 mM mannoheptulose, an inhibitor of glucose metabolism, was present in addition to glucose.

Dual effects of diazoxide on ATP-K+ currents recorded from an insulin-secreting cell line.

1. The effects of diazoxide on ATP-K+ channel currents, recorded from the insulin-secreting cell line, CRI-G1, were studied using patch-clamp techniques. 2.

Enhancement of desensitization of quisqualate-type glutamate receptor by the dissociative anaesthetic ketamine.

Application of ketamine (10(-4)-10(-3)mol l-1) to locust retractor unguis muscle produced a reversible, dose-dependent reduction in neurally evoked twitches, and blocked agonist-induced contractions. With increasing ketamine concentration (5 x 10(-5)-10(-3) mol l-1), the amplitude of glutamate potentials was reduced and dose-response curves for ionophoresis of L-glutamate were shifted to the right, particularly after concanavalin A treatment. Ketamine (10(-4) mol l-1) enhanced the rate of desensitization to consecutive pulses of L-glutamate and this action was eliminated by concanavalin A.

Effects of sulphonylureas and diazoxide on insulin secretion and nucleotide-sensitive channels in an insulin-secreting cell line.

1. The effects of various sulphonylureas and diazoxide on insulin secretion and the activity of various channels have been studied using tissue culture and patch-clamp methods in an insulin-secreting cell line derived from a rat islet cell tumour. 2.