Takuma T, Kuyatt B L, Baum B J
Biochem J. 1985 Apr 1;227(1):239-45. doi: 10.1042/bj2270239.
Ca2+ transport was studied by using basolateral plasma membrane vesicles from rat parotid gland prepared by a Percoll gradient centrifugation method. In these membrane vesicles, there were two Ca2+ transport systems; Na+/Ca2+ exchange and ATP-dependent Ca2+ transport. An outwardly directed Na+ gradient increased Ca2+ uptake. Ca2+ efflux from Ca2+-preloaded vesicles was stimulated by an inwardly directed Na+ gradient. However, Na+/Ca2+ exchange did not show any 'uphill' transport of Ca2+ against its own gradient. ATP-dependent Ca2+ transport exhibited 'uphill' transport. An inwardly directed Na+ gradient also decreased Ca2+ accumulation by ATP-dependent Ca2+ uptake. The inhibition of Ca2+ accumulation was proportional to the external Na+ level. Na+/Ca2+ exchange was inhibited by monensin, tetracaine and chlorpromazine, whereas ATP-dependent Ca2+ transport was inhibited by orthovanadate, tetracaine and chlorpromazine. Oligomycin had no effect on either system. These results suggest that in the parotid gland cellular free Ca2+ is extruded mainly by an ATP-dependent Ca2+ transport system, and Na+/Ca2+ exchange may modify the efficacy of that system.
采用通过Percoll梯度离心法制备的大鼠腮腺基底外侧质膜囊泡研究Ca2+转运。在这些膜囊泡中，存在两种Ca2+转运系统；Na+/Ca2+交换和ATP依赖的Ca2+转运。外向的Na+梯度增加Ca2+摄取。Ca2+预加载囊泡中的Ca2+外流受内向的Na+梯度刺激。然而，Na+/Ca2+交换未显示出任何逆自身梯度的Ca2+“上坡”转运。ATP依赖的Ca2+转运表现出“上坡”转运。内向的Na+梯度也通过ATP依赖的Ca2+摄取减少Ca2+积累。Ca2+积累的抑制与细胞外Na+水平成比例。Na+/Ca2+交换受莫能菌素、丁卡因和氯丙嗪抑制，而ATP依赖的Ca2+转运受原钒酸盐、丁卡因和氯丙嗪抑制。寡霉素对这两种系统均无影响。这些结果表明，在腮腺中，细胞内游离Ca2+主要通过ATP依赖的Ca2+转运系统排出，并且Na+/Ca2+交换可能会改变该系统的功效。
