Best L, Yates A P, Gordon C, Tomlinson S
Department of Medicine, University of Manchester, U.K.
Biochem Pharmacol. 1988 Dec 15;37(24):4611-5. doi: 10.1016/0006-2952(88)90328-0.
Cytosolic pH (pHi) of pancreatic islet cells was assessed using the fluorescent dye 2'7'-biscarboxyethyl-5'(6')-carboxyfluorescein (BCECF). pHi was rapidly lowered by addition of the sodium salt of a weak acid or by treatment with amiloride. In the latter case, no recovery of pHi occurred. NH4Cl produced a rise in pHi. Stimulation of islet cells with glyceraldehyde produced a sustained fall in pHi, whereas glucose and alpha-ketoisocaproate caused a small, gradual rise in pHi. Intracellular acidification, particularly with amiloride, resulted in an immediate potentiation of glucose-induced insulin secretion from perifused islets. In the case of weak acid treatment, subsequent removal of the weak acid produced a paradoxical stimulation of insulin release which was not observed upon removal of amiloride. NH4Cl produced a transient stimulation followed by a reduction in the rate of glucose-induced insulin secretion. A reduction in pHi, either in response to weak acid or amiloride treatment, was associated with a diminution in the rate of efflux of 86Rb+ and of 45Ca2+. Removal of weak acid produced a marked "rebound" stimulation of 86Rb+ and 45Ca2+ efflux. Treatment of islets with NH4Cl, either in the presence or absence of glucose or Ca2+, resulted in a marked stimulation of efflux of 86Rb+ and 45Ca2+. The stimulatory effect of NH4Cl on 45Ca2+ efflux was markedly impaired in the absence of Na+. It is concluded that pHi can influence the secretory activity of pancreatic islets, possibly via effects on potassium permeability and sodium-calcium exchange across the plasma membrane, resulting in altered mobilisation of calcium in the islet cell. However, it is unlikely that glucose or other nutrient stimuli activate islets solely via an effect on pHi.
使用荧光染料2'7'-双（羧乙基）-5'（6'）-羧基荧光素（BCECF）评估胰岛细胞的胞质pH（pHi）。添加弱酸的钠盐或用氨氯吡咪处理可使pHi迅速降低。在后一种情况下，pHi未恢复。氯化铵使pHi升高。用甘油醛刺激胰岛细胞导致pHi持续下降，而葡萄糖和α-酮异己酸引起pHi小幅、逐渐升高。细胞内酸化，尤其是氨氯吡咪引起的酸化，导致从灌流胰岛中葡萄糖诱导的胰岛素分泌立即增强。在用弱酸处理的情况下，随后去除弱酸会产生反常的胰岛素释放刺激，而去除氨氯吡咪时未观察到这种情况。氯化铵产生短暂刺激，随后葡萄糖诱导的胰岛素分泌速率降低。无论是对弱酸还是氨氯吡咪处理的反应，pHi降低都与86Rb +和45Ca2 +流出速率的降低有关。去除弱酸会产生明显的86Rb +和45Ca2 +流出“反弹”刺激。无论有无葡萄糖或Ca2 +，用氯化铵处理胰岛都会导致86Rb +和45Ca2 +流出明显增强。在没有Na +的情况下，氯化铵对45Ca2 +流出的刺激作用明显受损。结论是，pHi可能通过影响钾通透性和跨质膜的钠钙交换来影响胰岛的分泌活性，从而导致胰岛细胞中钙动员的改变。然而，葡萄糖或其他营养刺激物不太可能仅通过对pHi的影响来激活胰岛。
