Dipolo R, Beaugé L
Biochim Biophys Acta. 1982 May 21;688(1):237-45. doi: 10.1016/0005-2736(82)90599-5.
The effect of internal and external pH, on the components of the Ca2+ efflux have been investigated in internally displayed squid axons. (1) Internal pH: a fall in intracellular pH (below 7.3) inhibited both the ATP-dependent uncoupled (Ca2+ pump) (50% at pHi 6.3) and the Na+o-dependent Ca2+ efflux (forward Na+/Ca2+ exchange) (50% at pHi 6.8). Internal alkalinization of pH 8.8 had no effect on the uncoupled component but markedly increased (4-fold) the Na+o-dependent Ca2+ efflux. (2) External pH: altering the external pH from 7.3 to 9.0 had no effect on the Na+o-dependent Ca2+ efflux mechanism. In the absence of Ca2+o, alkalinization to pHo 8.8 caused a reduction in the magnitude of the uncoupled Ca2+ pump. This inhibition is markedly enhanced by the presence of Ca2+ in the external medium. As for the case of the sarcoplasmic reticulum Ca2+-ATPase, this combined inhibitory effect of high pHo and Ca2+o is most probably related to a reversal of the cycle of the ATP driven Ca2+ pump. The marked differences in the pH dependence of the components of the Ca2+ efflux support the model of two separate mechanisms of Ca2+ extrusion in squid axons: Ca2+ pump and Na+/Ca2+ exchange.
在内部呈现的枪乌贼轴突中，研究了细胞内外pH值对Ca2+外流成分的影响。(1) 细胞内pH值：细胞内pH值下降（低于7.3）会抑制ATP依赖的非偶联（Ca2+泵）（在细胞内pH值为6.3时抑制50%）和Na+o依赖的Ca2+外流（正向Na+/Ca2+交换）（在细胞内pH值为6.8时抑制50%）。细胞内碱化至pH值8.8对非偶联成分没有影响，但显著增加（4倍）了Na+o依赖的Ca2+外流。(2) 细胞外pH值：将细胞外pH值从7.3改变到9.0对Na+o依赖的Ca2+外流机制没有影响。在没有Ca2+o的情况下，碱化至细胞外pH值8.8会导致非偶联Ca2+泵的幅度降低。外部介质中存在Ca2+会显著增强这种抑制作用。至于肌浆网Ca2+-ATP酶的情况，高细胞外pH值和Ca2+o的这种联合抑制作用很可能与ATP驱动的Ca2+泵循环的逆转有关。Ca2+外流成分对pH值依赖性的显著差异支持了枪乌贼轴突中Ca2+外排的两种独立机制模型：Ca2+泵和Na+/Ca2+交换。
