Gribble F M, Ashcroft F M
University Laboratory of Physiology, Oxford, UK.
Diabetologia. 1999 Jul;42(7):845-8. doi: 10.1007/s001250051236.
AIMS/HYPOTHESIS: To investigate the tissue specificity of gliclazide for cloned beta-cell, cardiac and smooth muscle ATP-sensitive K-channels (K(ATP) channels). These channels share a common pore-forming subunit, Kir6.2, which associates with different sulphonylurea receptor isoforms (SUR1 in beta-cells, SUR2A in heart, SUR2B in smooth muscle).
Kir6.2 was coexpressed with SUR1, SUR2A or SUR2B in Xenopus oocytes, and channel activity was measured by recording macroscopic currents in giant inside-out membrane patches. Gliclazide was added to the intracellular membrane surface.
We reported previously that Kir6.2-SUR1 currents are blocked at two sites by tolbutamide: a high-affinity site on SUR1 and a low-affinity site on Kir6.2. We now show that gliclazide also inhibits beta-cell K(ATP) channels at two sites: a high-affinity site, which is half-maximally blocked (Ki) at 50 +/- 7 nmol/l (n = 8) and a low-affinity site with a Ki of 3.0 +/- 0.6 mmol/l (n = 4). The high-affinity site on SUR1 was thus about 40-fold more sensitive to gliclazide than to tolbutamide (Ki approximately 2 micromol/l). Cloned cardiac and smooth muscle K(ATP) channels did not show high-affinity block by gliclazide. Kir6.2-SUR2A currents exhibited a single low-affinity site with a Ki of 0.8 +/- 0.1 mmol/l (n = 5), which is likely to reside on the Kir6.2 subunit.
CONCLUSION/INTERPRETATION: Our results show that gliclazide is a sulphonylurea with high affinity and strong selectivity for the beta-cell type of K(ATP) channel.
目的/假设：研究格列齐特对克隆的β细胞、心脏和平滑肌三磷酸腺苷敏感性钾通道（K(ATP)通道）的组织特异性。这些通道共享一个共同的孔形成亚基Kir6.2，它与不同的磺脲类受体亚型相关联（β细胞中的SUR1、心脏中的SUR2A、平滑肌中的SUR2B）。
将Kir6.2与SUR1、SUR2A或SUR2B在非洲爪蟾卵母细胞中共表达，并通过记录巨大的内翻膜片上的宏观电流来测量通道活性。将格列齐特添加到细胞内膜表面。
我们之前报道过，甲苯磺丁脲在两个位点阻断Kir6.2-SUR1电流：SUR1上的一个高亲和力位点和Kir6.2上的一个低亲和力位点。我们现在表明，格列齐特也在两个位点抑制β细胞K(ATP)通道：一个高亲和力位点，在50±7 nmol/l（n = 8）时半数最大阻断（Ki），以及一个Ki为3.0±0.6 mmol/l（n = 4）的低亲和力位点。因此，SUR1上的高亲和力位点对格列齐特的敏感性比对甲苯磺丁脲（Ki约为2 μmol/l）高约40倍。克隆的心脏和平滑肌K(ATP)通道未显示被格列齐特高亲和力阻断。Kir6.2-SUR2A电流表现出一个单一的低亲和力位点，Ki为0.8±0.1 mmol/l（n = 5），该位点可能位于Kir6.2亚基上。
结论/解读：我们的结果表明，格列齐特是一种对β细胞型K(ATP)通道具有高亲和力和强选择性的磺脲类药物。
