Mg<sup>2+</sup>‐dependent inhibition of K<sub>ATP</sub> by sulphonylureas in CRI‐G1 insulin‐secreting cells

Lee, K.; Ozanne, Susan E.; Hales, C. N.; Ashford, M. L. J.

doi:10.1111/j.1476-5381.1994.tb14783.x

Cited by 26 publications

(22 citation statements)

References 30 publications

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“…We tested for a role of the presumed cytoplasmic domains of K ir 6.2 in ATP sensitivity of the K ATP channel because cytoplasmic but not external ATP inhibits the channel (17, 18) and cytoplasmic but not external mild trypsin treatment diminishes ATP sensitivity (19)(20)(21). We mutated K ir 6.2 rather than SUR1 for several reasons.…”

Section: Mouse Sur1 and Mouse K Ir 62 Coexpressed In Xenopusmentioning

confidence: 99%

K _ATP channel inhibition by ATP requires distinct functional domains of the cytoplasmic C terminus of the pore-forming subunit

Drain

Wang

1998

Proc. Natl. Acad. Sci. U.S.A.

187

228

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ATP-sensitive potassium (''K ATP '') channels are rapidly inhibited by intracellular ATP. This inhibition plays a crucial role in the coupling of electrical activity to energy metabolism in a variety of cells. The K ATP channel is formed from four each of a sulfonylurea receptor (SUR) regulatory subunit and an inwardly rectifying potassium (K ir 6.2) pore-forming subunit. We used systematic chimeric and point mutagenesis, combined with patch-clamp recording, to investigate the molecular basis of ATP-dependent inhibition gating of mouse pancreatic ␤ cell K ATP channels expressed in Xenopus oocytes. We identified distinct functional domains of the presumed cytoplasmic C-terminal segment of the K ir 6.2 subunit that play an important role in this inhibition. Our results suggest that one domain is associated with inhibitory ATP binding and another with gate closure.The ATP-sensitive potassium (K ATP ) channel couples membrane electrical activity to energy metabolism in a variety of cells and is important in several physiological systems. In pancreatic ␤ cells, for example, it is essential for coupling the rate of insulin release to blood glucose levels. Although the channel's name reflects its characteristic inhibition by intracellular ATP, little is known about the molecular nature of this property.To understand the molecular mechanisms underlying ATPdependent inhibition gating in the K ATP channel, one must identify those parts of the channel complex that form the ATP-binding site, the inhibition gate, and the ''linkage'' domains handling signal flow between them. The K ATP channel is assembled from four each of two subunit types, a regulatory sulfonylurea receptor (SUR) or SUR1 and a potassium poreforming subunit or K ir 6.2 (1-4). SUR1 is a member of the ATP-binding cassette (ABC) family of proteins featuring two cytoplasmic nucleotide-binding folds, viewed initially as likely mediators of inhibition by ATP (5, 6). However, a mutant K ir 6.2 in which the C-terminal 26 residues are deleted remarkably gives rise to potassium channels that retain much ATP sensitivity in the absence of SUR1 (7). The truncation does, however, diminish ATP sensitivity of the K ATP channel 10-fold, as does SUR2 when coexpressed with wild-type K ir 6.2 (6). These results have led to opposing models in which ATP acts either on K ir 6.2 or on SUR to inhibit the K ATP channel.We tested whether major components of the ATPdependent inhibition gating mechanism reside in the poreforming subunit. By systematically mutating K ir 6.2, we localized molecular components of ATP-dependent inhibition gating to distinct regions of its cytoplasmic C-terminal segment. Our results confirm and extend the findings of Tucker et al. (7) that the primary site of action of inhibitory ATP lies on K ir 6.2. We go on to show that one of the regions we identified is likely associated with inhibitory ATP binding, whereas a second region appears to be associated with inhibition gate closure. MATERIALS AND METHODSMolecular Biology. Cloning of mouse SUR1 and K ...

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Section: Mouse Sur1 and Mouse K Ir 62 Coexpressed In Xenopusmentioning

confidence: 99%

K _ATP channel inhibition by ATP requires distinct functional domains of the cytoplasmic C terminus of the pore-forming subunit

Drain

Wang

1998

Proc. Natl. Acad. Sci. U.S.A.

187

228

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“…These findings suggest the following: The specific binding site for PCOs is completely different from that for sulfonylureas, because the same phenomenon was observed using different PCOs such as benzopyran or a nicorandil-like structure. Recently, the specific binding sites for sulfonylureas and ATP-sensitive potassium channels were reported to be separate molecular entities, since the cloned channels were not inhibited by a micromolar concentration of glibenclamide, although they were activated by the PCO pinacidil (38,39). In addition, Bray and Quast (15) This study showed that the ISK(Ca) selective blocker apamin (30) also displaced the specific binding of [3H]glibenclamide in both membrane preparations in a concentration-dependent manner.…”

Section: The Effects Of Nip-121 Levcromakalim and Nicorandil On [Jhjmentioning

confidence: 99%

The Effects of Potassium Channel Openers and Blockers on the Specific Binding Sites for [3H]Glibenclamide in Rat Tissues

Yamashita

Masuda

Tanaka

1995

Japanese Journal of Pharmacology

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ABSTRACT-The effects of K+ channel openers (PCOs), NIP-121, levcromakalim and nicorandil, and the blockers of the specific binding sites for [3H]glibenclamide, ATP-sensitive K+ channel blocker, were investigated in rat brain and cardiac ventricle membrane preparations. When the microsomes were incubated with [3H]glibenclamide, the specific glibenclamide binding was fully inhibited by unlabeled glibenclamide (1 pM) and apamin (100 pM). However, the specific glibenclamide binding was not influenced by excess NIP-121, levcromakalim and nicorandil, although glibenclamide antagonized the increase in the 86Rb+ efflux by PCOs. On the other hand, the binding of [3H]glibenclamide after a long pre-incubation (60 min) at 37'C with NIP-121 and levcromakalim at pharmacological effective concentrations (10 nM to 1 pM) was significantly influenced. Both PCOs partially reduced both Kd and Bmax values of the specific [3H]-glibenclamide binding in a concentration-dependent manner that was not regulated by GTPIS. The doseeffect relationships for the Bmax's of NIP-121 and levcromakalim seemed similar to those for vasorelaxation. These findings indicate that the pharmacological effect of PCO may be caused by the binding to its own specific sites but not to the specific sulfonylurea sites. The binding of PCOs may inhibit, in a negative allosteric manner the binding of sulfonylureas.

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“…Flow debt repayment during the first re-perfusion minute after three periods of forearm ischaemia during concomitant infusion of placebo (R) and during the repeat (A) with placebo in the control group (n = 6) or with glibenclamide in the experimental group (n = 12). p-values refer to ANOVA with repeated measures; * post-hoc t-test p < 0.05, mean ± SEM including localized decreases of ATP-concentration in a submembranous compartment of the cell [29,30], endothelial release of a hyperpolarizing factor (endothelium derived hyperpolarising factor) [31], an increase in the intracellular concentration of adenosine-5′-diphosphate [32], an increase in interstitial concentrations of the ATP-degradation product adenosine [33], and alterations in concentrations of Mg 2 + [34] or pH [35].…”

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Blockade of vascular ATP-sensitive potassium channels reduces the vasodilator response to ischaemia in humans

et al. 1996

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In 1983, Noma [1] was the first to describe that an outward potassium current increased significantly when guinea pig or rabbit cardiac muscle cells were subjected to hypoxia. This current was caused by the activation of potassium channels, which was independent of the intracellular Ca 2+ concentration, but dependent on the intracellular concentration of adenosine-5 ′-triphosphate ([ATP] i ). These so-called ATPsensitive potassium (K ATP ) channels were suggested to play a cardioprotective role during ischaemia. Later, K ATP channels were also found in skeletal muscle [2], smooth muscle [3] and pancreatic beta cells [4] from animals. In pancreatic beta cells the K ATP channels mediate insulin secretion [5] and are a target for sulphonylurea derivatives in the treatment of non-insulin-dependent diabetes mellitus (NIDDM) [6]. Sulphonylurea derivatives are highly specific in blocking pancreatic and cardiovascular K ATP channels, and Diabetologia (1996Diabetologia ( ) 39: 1562Diabetologia ( -1568 Blockade of vascular ATP-sensitive potassium channels reduces the vasodilator response to ischaemia in humans Summary Experimental data show that ATP-sensitive potassium (K ATP ) channels not only occur in pancreatic beta cells, but also in the cardiovascular system, where they mediate important cardioprotective mechanisms. Sulphonylurea derivatives can block the cardiovascular K ATP channels and may therefore interfere with these cardioprotective mechanisms. Therefore, it is of clinical importance to investigate whether sulphonylurea derivatives interact with vascular K ATP channels in humans. Using venous-occlusion strain-gauge plethysmography, we investigated whether ischaemia-induced reactive hyperaemia is reduced by the sulphonylurea derivative glibenclamide in 12 healthy male non-smoking volunteers. Forearm vasodilator responses to three periods of arterial occlusion (2, 5 and 13 min) during concomitant infusion of placebo into the brachial artery were compared with responses during concomitant intra-arterial infusion of glibenclamide (0.33A control study (n = 6) showed that time itself did not change the vasodilator response to ischaemia.Glibenclamide significantly increased minimal vascular resistance (from 2.1 ± 0.1 to 2.3 ± 0.2 arbitrary units, Student's t-test: p = 0.01), and reduced mean forearm blood flow (from 37.5 ± 2.0 to 35.4 ± 2.0 ml ⋅ min -1 ⋅ dl -1 after 13 min occlusion, ANOVA with repeated measures: p = 0.006) and flow debt repayment during the first reperfusion minute (ANOVA with repeated measures: p = 0.04). In contrast, total flow debt repayment was not affected. Infusion of glibenclamide into the brachial artery resulted in local concentrations in the clinically relevant range, whereas the systemic concentration remained too low to elicit hypoglycaemic effects. Our results suggest that therapeutic concentrations of glibenclamide induce a slight but significant reduction in the early and peak vasodilation during reactive hyperaemia.

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Mg²⁺‐dependent inhibition of K_ATP by sulphonylureas in CRI‐G1 insulin‐secreting cells

Cited by 26 publications

References 30 publications

K _ATP channel inhibition by ATP requires distinct functional domains of the cytoplasmic C terminus of the pore-forming subunit

K _ATP channel inhibition by ATP requires distinct functional domains of the cytoplasmic C terminus of the pore-forming subunit

The Effects of Potassium Channel Openers and Blockers on the Specific Binding Sites for [3H]Glibenclamide in Rat Tissues

Blockade of vascular ATP-sensitive potassium channels reduces the vasodilator response to ischaemia in humans

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Mg2+‐dependent inhibition of KATP by sulphonylureas in CRI‐G1 insulin‐secreting cells

Cited by 26 publications

References 30 publications

K ATP channel inhibition by ATP requires distinct functional domains of the cytoplasmic C terminus of the pore-forming subunit

K ATP channel inhibition by ATP requires distinct functional domains of the cytoplasmic C terminus of the pore-forming subunit

The Effects of Potassium Channel Openers and Blockers on the Specific Binding Sites for [3H]Glibenclamide in Rat Tissues

Blockade of vascular ATP-sensitive potassium channels reduces the vasodilator response to ischaemia in humans

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Resources

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Mg²⁺‐dependent inhibition of K_ATP by sulphonylureas in CRI‐G1 insulin‐secreting cells

K _ATP channel inhibition by ATP requires distinct functional domains of the cytoplasmic C terminus of the pore-forming subunit

K _ATP channel inhibition by ATP requires distinct functional domains of the cytoplasmic C terminus of the pore-forming subunit