Sener Abdullah, Jijakli Hassan, Zahedi Asl Saleh, Courtois Philippe, Yates Allen P, Meuris Sylvain, Best Leonard C, Malaisse Willy J
Laboratory of Experimental Hormonology, Brussels Free University, Brussels, Belgium.
Am J Physiol Endocrinol Metab. 2007 Jun;292(6):E1624-30. doi: 10.1152/ajpendo.00631.2006. Epub 2007 Feb 6.
The presence of carbonic anhydrase (type V) was recently documented in rat and mouse pancreatic islet beta-cells by immunostaining and Western blotting. In the present study, the activity of carbonic anhydrase was measured in rat islet homogenates and shown to be about four times lower than in rat parotid cells. The pattern for the inhibitory action of acetazolamide on carbonic anhydrase activity also differed in islet and parotid cell homogenates, suggesting the presence of different isoenzymes. NaN3 inhibited carbonic anhydrase activity in islet homogenates and both D-[U-14C]glucose oxidation and glucose-stimulated insulin secretion. Acetazolamide (0.3-10.0 mM) also decreased glucose-induced insulin output but failed to affect adversely D-[U-14C]glucose oxidation, although it inhibited the conversion of D-[5-3H]glucose to [3H]OH and that of D-[U-14C]glucose to acidic metabolites. Hydrochlorothiazide (3.0-10.0 mM), which also caused a concentration-related inhibition of the secretory response, like acetazolamide (5.0-10.0 mM), decreased H(14)CO3- production from D-[U-14C]glucose (16.7 mM). Acetazolamide (5.0 mM) did not affect the activity of volume-sensitive anion channels in beta-cells but lowered intracellular pH and adversely affected both the bioelectrical response to d-glucose and its effect on the cytosolic concentration of Ca2+ in these cells. The lowering of cellular pH by acetazolamide, which could well be due to inhibition of carbonic anhydrase, might in turn account for inhibition of glycolysis. The perturbation of stimulus-secretion coupling in the beta-cells exposed to acetazolamide may thus involve impaired circulation in the pyruvate-malate shuttle, altered mitochondrial Ca2+ accumulation, and perturbation of Cl- fluxes, resulting in both decreased bioelectrical activity and insulin release.
最近通过免疫染色和蛋白质印迹法在大鼠和小鼠胰岛β细胞中证实了碳酸酐酶（Ⅴ型）的存在。在本研究中，测定了大鼠胰岛匀浆中碳酸酐酶的活性，结果显示其活性比大鼠腮腺细胞中的活性低约四倍。乙酰唑胺对碳酸酐酶活性的抑制作用模式在胰岛和腮腺细胞匀浆中也有所不同，这表明存在不同的同工酶。NaN₃抑制胰岛匀浆中的碳酸酐酶活性以及D-[U-¹⁴C]葡萄糖氧化和葡萄糖刺激的胰岛素分泌。乙酰唑胺（0.3 - 10.0 mM）也降低了葡萄糖诱导的胰岛素分泌，但未能对D-[U-¹⁴C]葡萄糖氧化产生不利影响，尽管它抑制了D-[5-³H]葡萄糖向[³H]OH的转化以及D-[U-¹⁴C]葡萄糖向酸性代谢产物的转化。氢氯噻嗪（3.0 - 10.0 mM）也像乙酰唑胺（5.0 - 10.0 mM）一样引起与浓度相关的分泌反应抑制，降低了D-[U-¹⁴C]葡萄糖（16.7 mM）产生的H¹⁴CO₃⁻。乙酰唑胺（5.0 mM）不影响β细胞中容积敏感性阴离子通道的活性，但降低了细胞内pH值，并对d-葡萄糖的生物电反应及其对这些细胞中细胞质Ca²⁺浓度的影响产生不利影响。乙酰唑胺引起的细胞pH值降低很可能是由于碳酸酐酶的抑制，这反过来可能导致糖酵解受到抑制。因此，暴露于乙酰唑胺的β细胞中刺激-分泌偶联的扰动可能涉及丙酮酸-苹果酸穿梭循环受损、线粒体Ca²⁺积累改变以及Cl⁻通量扰动，从而导致生物电活动和胰岛素释放均减少。
