Glibenclamide binding to sulphonylurea receptor subtypes: dependence on adenine nucleotides

Abstract

1 ATP-sensitive K + channels are composed of pore-forming subunits Kir6.2 and of sulphonylurea receptors (SURs); the latter are the target of the hypoglycaemic sulphonylureas like glibenclamide. Here, we report on the negative allosteric modulation by MgATP and MgADP of glibenclamide binding to SUR1 and to SUR2 mutants with high glibenclamide anity, SUR2A(Y1206S) and SUR2B(Y1206S). 2 ATP, in the presence of an ATP-regenerating system to oppose hydrolysis during incubation, inhibited glibenclamide binding to SUR1 and SUR2B(Y1206S) by *60%, to SUR2A(Y1206S) by 21%). Inhibition curves for the SUR2(Y1206S) isoforms were monophasic with IC 50 values of 5 ± 10 mM; the curve for SUR1 was biphasic (IC 50 values 4.7 and 1300 mM). 3 Glibenclamide inhibition curves for ADP, performed in the presence of an ATP-consuming system to oppose ATP formation from ADP, were generally shifted rightwards and showed positive cooperativity, in particular with the SUR2(Y1206S) isoforms. 4 In the absence of the coupled enzyme systems, inhibition curves of MgATP or MgADP were generally shifted leftwards. This indicated synergy of MgATP and MgATP in acting together. 5 Coexpression of SUR1 and SUR2B(Y1206S) with Kir6.2 reduced both potency and ecacy of ATP in inhibiting glibenclamide binding; this was particularly marked for Kir6.2/SUR1. 6 The data show (a) that the inhibitory eects of ATP and ADP on glibenclamide binding dier from one another, (b) that they depend on the SUR subtype, and (c) that they are weakened by coexpression with Kir6.2.

Mg2+ sensitizes KATP channels to inhibition by DIDS: dependence on the sulphonylurea receptor subunit

“…. Values at 228C were determined for this study, values at 378C are from Hambrock et al (2002) and Table 4. 4 The two-component ®t was signi®cantly better than the ®t of the Hill equation (eqn (1)) which gave an IC 50 value of 13 (10,17) mM and a Hill coecient of 0.74+0.1.…”

“…However, these complexities may also be interpreted assuming that SUR expressed alone forms tetramers (LoÈ er-Walz et al, 2002;Hambrock et al, 2002) and that site-site interactions between subunits occur. More importantly, the inhibition of [ 3 H]-glibenclamide binding to the Kir6.2/SUR2B(Y1206S) complex by DIDS (30 mM) was entirely reversible with a half-time of 4 min.…”

Glibenclamide-Induced Apoptosis Is Specifically Enhanced by Expression of the Sulfonylurea Receptor Isoform SUR1 but Not by Expression of SUR2B or the Mutant SUR1(M1289T)

“…Alternative splicing of the SUR2 gene leads to expression of either SUR2A, predominantly found in heart and skeletal muscle, or SUR2B, typically occurring in smooth vascular muscle (Gribble and Reimann, 2003). To some extent, SUR1 and SUR2 show inverse pharmacological profiles; SUR1 exhibits high affinity for several sulfonylureas but low affinity for most K ATP channel openers, whereas SUR2 shows lower affinity for sulfonylureas and high affinity for openers (Schwanstecher et al, 1998;Hambrock et al, 2002).In the pancreatic ␤-cell, K ATP channels (constituted by SUR1 and Kir6.2) are essential for triggering insulin secretion via membrane depolarization. High blood glucose concentrations lead to an elevated ATP/ADP ratio and result in closure of K ATP channels, opening of voltage-dependent Ca 2ϩ channels, and release of insulin-containing vesicles (Ashcroft, 2000;Gribble and Reimann, 2003;Bryan et al, 2004).…”

“…Alternative splicing of the SUR2 gene leads to expression of either SUR2A, predominantly found in heart and skeletal muscle, or SUR2B, typically occurring in smooth vascular muscle (Gribble and Reimann, 2003). To some extent, SUR1 and SUR2 show inverse pharmacological profiles; SUR1 exhibits high affinity for several sulfonylureas but low affinity for most K ATP channel openers, whereas SUR2 shows lower affinity for sulfonylureas and high affinity for openers (Schwanstecher et al, 1998;Hambrock et al, 2002).…”

Metal-Based Optical Probes for Live Cell Imaging of Nitroxyl (HNO)

“…Strategies to label particular cellular organelles include genetically encoded fusion protein tags, [40][41][42] synthetic peptides, [43][44][45][46] and smallmolecule vectors [47][48][49] to deliver HNO sensors to programmed locations within the cell.…”