Anwer M S
Department of Medicine, Tufts University School of Veterinary Medicine, North Grafton, Massachusetts 01536.
Hepatology. 1993 Aug;18(2):433-9.
Calcium ionophores such as ionomycin and A23187 are often used to determine the role of intracellular Ca++ in cellular processes. Ionomycin but not Ca+(+)-mobilizing agonists increases basal intracellular pH in hepatocytes. To explain this difference in effects of agents that increase intracellular Ca++ concentration, the mechanism of ionomycin-induced increases in basal intracellular pH in isolated rat hepatocytes was studied. Changes in intracellular pH and intracellular Ca++ concentration were measured with the fluorescent probes BCECF (2',7'-bis-2-[carboxyethyl ester]-5[6]carboxyfluorescein) and quin-2, respectively. Ionomycin produced dose-dependent increases in intracellular pH and intracellular Ca++ concentration, with the increase in intracellular Ca++ concentration preceded by the increase in intracellular pH. Ionomycin-induced increases in intracellular pH were not affected by 1 mmol/L amiloride, 100 mumol/L diisothiocyanostilbene disulfonate or removal of extracellular Na+, indicating that the effect is not mediated by Na+/H+ exchange, Cl-/HCO3- exchange or Na+/HCO3- cotransport. Ionomycin failed to increase intracellular pH or intracellular Ca++ concentration in the absence of extracellular Ca++, and both intracellular pH and intracellular Ca++ concentration increased promptly when extracellular Ca++ was reintroduced. Ionomycin-induced increases in intracellular Ca++ concentration but not intracellular pH were smaller in hepatocytes loaded with the Ca++ buffering agent MAPTA. Thapsigargin increased intracellular Ca++ concentration but failed to increase intracellular pH. Thus the effect of ionomycin is independent of the effect of ionomycin on intracellular Ca++ concentration and dependent on extracellular intracellular Ca++ concentration. Experimental conditions that produce cell depolarization did not increase basal intracellular pH but lowered ionomycin-induced increases in intracellular pH by 25% without affecting increases in intracellular Ca++ concentration.(ABSTRACT TRUNCATED AT 250 WORDS)
钙离子载体如离子霉素和A23187常用于确定细胞内钙离子在细胞过程中的作用。离子霉素而非钙离子动员激动剂会增加肝细胞的基础细胞内pH值。为解释增加细胞内钙离子浓度的药物在作用上的这种差异，研究了离子霉素诱导分离的大鼠肝细胞基础细胞内pH值升高的机制。分别用荧光探针BCECF（2'，7'-双-2-[羧乙基酯]-5[6]羧基荧光素）和喹啉-2测量细胞内pH值和细胞内钙离子浓度的变化。离子霉素使细胞内pH值和细胞内钙离子浓度呈剂量依赖性增加，细胞内钙离子浓度的增加先于细胞内pH值的增加。离子霉素诱导的细胞内pH值升高不受1 mmol/L氨氯吡咪、100 μmol/L二异硫氰酸芪二磺酸或细胞外钠离子去除的影响，表明该作用不是由钠/氢交换、氯/碳酸氢根交换或钠/碳酸氢根共转运介导的。在没有细胞外钙离子的情况下，离子霉素未能增加细胞内pH值或细胞内钙离子浓度，当重新引入细胞外钙离子时，细胞内pH值和细胞内钙离子浓度迅速增加。在加载钙离子缓冲剂MAPTA的肝细胞中，离子霉素诱导的细胞内钙离子浓度增加但细胞内pH值增加较小。毒胡萝卜素增加细胞内钙离子浓度但未能增加细胞内pH值。因此，离子霉素的作用独立于其对细胞内钙离子浓度的影响，且依赖于细胞外钙离子浓度。产生细胞去极化的实验条件并未增加基础细胞内pH值，但使离子霉素诱导的细胞内pH值升高降低了25%，而不影响细胞内钙离子浓度的增加。（摘要截短于250字）
