Pickkers P, Garcha R S, Schachter M, Smits P, Hughes A D
Department of Pharmacology, University Hospital Nijmegen, Nijmegen, The Netherlands.
Hypertension. 1999 Apr;33(4):1043-8. doi: 10.1161/01.hyp.33.4.1043.
Hydrochlorothiazide has been shown to exert direct vasodilator effects by activation of calcium-activated potassium (KCa) channels in human and guinea pig isolated resistance arteries. Since hydrochlorothiazide binds to and inhibits the enzyme carbonic anhydrase and because KCa channel activation is pH sensitive, we investigated the role of intracellular and extracellular carbonic anhydrase in the vascular effects of thiazide diuretics. Small arteries were isolated from guinea pig mesentery and studied by use of a microvascular myograph technique. In some experiments, tone and intracellular pH (pHi) were measured simultaneously with 2', 7'-bis(2-carboxyethyl)-5(6)'-carboxyfluorescein (BCECF-AM). Bendroflumethiazide, a thiazide diuretic with minimal inhibitory effects on carbonic anhydrase, had little effect on noradrenaline-induced tone (16+/-8% relaxation) compared with hydrochlorothiazide (74+/-12% relaxation). In contrast to hydrochlorothiazide, the action of bendroflumethiazide was unaffected by 100 nmol/L charybdotoxin, a selective blocker of KCa channels. All inhibitors of carbonic anhydrase relaxed noradrenaline-induced tone in a concentration-dependent manner, and this effect was blocked by charybdotoxin. Hydrochlorothiazide and the inhibitors of carbonic anhydrase failed to relax tone induced by a depolarizing potassium solution. Acetazolamide and hydrochlorothiazide increased pHi by 0.27+/-0.07 and 0.21+/-0.04, respectively, whereas bendroflumethiazide had a much smaller effect: 0.06+/-0.03. The rise in pHi induced by any agent was not inhibited by charybdotoxin. The vasorelaxant effect of hydrochlorothiazide is shared by other inhibitors of carbonic anhydrase. Inhibitors of carbonic anhydrase, but not bendroflumethiazide, cause intracellular alkalinization, which is associated with KCa channel opening. These data suggest that the vasodilator effect of thiazide diuretics results primarily from inhibition of vascular smooth muscle cell carbonic anhydrase, which results in a rise in pHI, leading to KCa channel activation and vasorelaxation.
氢氯噻嗪已被证明可通过激活人和豚鼠离体阻力动脉中的钙激活钾（KCa）通道发挥直接血管舒张作用。由于氢氯噻嗪与碳酸酐酶结合并抑制该酶，且KCa通道激活对pH敏感，我们研究了细胞内和细胞外碳酸酐酶在噻嗪类利尿剂血管效应中的作用。从小鼠肠系膜分离出小动脉，并使用微血管肌动描记术进行研究。在一些实验中，使用2'，7'-双（2-羧乙基）-5（6）'-羧基荧光素（BCECF-AM）同时测量张力和细胞内pH（pHi）。与氢氯噻嗪（74±12%舒张）相比，对碳酸酐酶抑制作用最小的噻嗪类利尿剂苄氟噻嗪对去甲肾上腺素诱导的张力几乎没有影响（16±8%舒张）。与氢氯噻嗪相反，苄氟噻嗪的作用不受100 nmol/L卡律毒素（一种KCa通道的选择性阻滞剂）的影响。所有碳酸酐酶抑制剂均以浓度依赖性方式舒张去甲肾上腺素诱导的张力，且该效应被卡律毒素阻断。氢氯噻嗪和碳酸酐酶抑制剂未能舒张去极化钾溶液诱导的张力。乙酰唑胺和氢氯噻嗪分别使pHi升高0.27±0.07和0.21±0.04，而苄氟噻嗪的作用则小得多：0.06±0.03。任何药物诱导的pHi升高均未被卡律毒素抑制。氢氯噻嗪的血管舒张作用与其他碳酸酐酶抑制剂相同。碳酸酐酶抑制剂而非苄氟噻嗪会导致细胞内碱化，这与KCa通道开放有关。这些数据表明，噻嗪类利尿剂的血管舒张作用主要源于对血管平滑肌细胞碳酸酐酶的抑制，这导致pHi升高，进而导致KCa通道激活和血管舒张。
