Lebrun P, Malaisse W J, Herchuelz A
Biochim Biophys Acta. 1982 Dec 30;721(4):357-65. doi: 10.1016/0167-4889(82)90090-8.
The removal of extracellular HCO3- together with a decrease in pCO2, in order to maintain a normal extracellular pH, caused a sustained increase of intracellular pH in rat pancreatic islets. This increase was more marked in glucose-deprived than in glucose-stimulated islets, and was associated with a facilitation of 45Ca efflux from the glucose-deprived islets. Such a facilitation was slightly reduced in the absence of extracellular Ca2+ and abolished at low extracellular Na+ concentration. It failed to occur in glucose-stimulated islets, whether in the presence or absence of extracellular Ca2+. The removal of HCO3- and decrease in the pCO2 also reduced the magnitude of both the secondary rise in 45Ca efflux and stimulation of insulin release normally evoked by an increase in glucose concentration. These findings suggest that changes in intracellular pH affect both the outflow of Ca2+ from islet cells as mediated by Na+ -Ca2+ countertransport and the inflow of Ca2+ by gated Ca2+ channels. The experimental data are also compatible with the view that islet cells are equipped with an active process of bicarbonate-chloride exchange involved in the regulation of intracellular pH.
为维持细胞外pH正常，去除细胞外HCO₃⁻并降低pCO₂，导致大鼠胰岛细胞内pH持续升高。这种升高在葡萄糖缺乏的胰岛中比在葡萄糖刺激的胰岛中更明显，并且与葡萄糖缺乏的胰岛中⁴⁵Ca外流的促进有关。在没有细胞外Ca²⁺的情况下，这种促进作用略有降低，而在低细胞外Na⁺浓度时则被消除。无论有无细胞外Ca²⁺，在葡萄糖刺激的胰岛中均未出现这种情况。去除HCO₃⁻和降低pCO₂也降低了通常由葡萄糖浓度升高引起的⁴⁵Ca外流的二次升高幅度和胰岛素释放的刺激程度。这些发现表明，细胞内pH的变化既影响由Na⁺-Ca²⁺逆向转运介导的Ca²⁺从胰岛细胞的流出，也影响通过门控Ca²⁺通道的Ca²⁺流入。实验数据也与胰岛细胞配备有参与细胞内pH调节的碳酸氢盐-氯交换的活跃过程这一观点相一致。
