Sakai Y, Grover A K, Fox J A, Daniel E E
Can J Physiol Pharmacol. 1983 Jul;61(7):699-704. doi: 10.1139/y83-108.
Calcium movements across plasma membrane enriched vesicles isolated from canine gastric corpus smooth muscle were investigated. The ATP-dependent Ca2+ uptake increased with time up to 10 min. The uptake for the initial 2-min period was approximately linear with time. The apparent initial velocity of the ATP-dependent Ca2+ uptake increased monotonically with free Ca2+ concentration from 0.1 to 2 microM, and further increases in free Ca2+ concentration did not increase the Ca2+ uptake. The free Ca2+ dependence curve could be described with a Hill coefficient of approximately 1.0 and Km of 0.85 +/- 0.01 microM for free Ca2+ concentration. Passive Ca2+ uptake (reaction time = 1 h) also increased with increasing free Ca2+ concentrations from 0.02 to 4.0 mM. Dilution of loaded vesicles in isotonic media containing EGTA led to initial rapid loss (less than 1 min) followed by a slower release which showed simple exponential decay. The t 1/2 values of the slower Ca2+ loss from these vesicles were 16.1 +/- 0.9 min (actively loaded n = 5) and 18.4 +/- 0.9 min (passively loaded n = 3), respectively. Dilution in isotonic medium containing both EGTA and A23187 released all the sequestered Ca2+ from these loaded vesicles.
对从犬胃体平滑肌分离的富含质膜的囊泡中的钙转运进行了研究。ATP 依赖的 Ca2+摄取在长达 10 分钟的时间内随时间增加。最初 2 分钟期间的摄取与时间大致呈线性关系。ATP 依赖的 Ca2+摄取的表观初始速度随游离 Ca2+浓度从 0.1 微摩尔增加到 2 微摩尔而单调增加，游离 Ca2+浓度进一步增加并未增加 Ca2+摄取。游离 Ca2+依赖性曲线可用 Hill 系数约为 1.0 和游离 Ca2+浓度的 Km 为 0.85±0.01 微摩尔来描述。被动 Ca2+摄取（反应时间 = 1 小时）也随着游离 Ca2+浓度从 0.02 毫摩尔增加到 4.0 毫摩尔而增加。在含有 EGTA 的等渗介质中稀释加载的囊泡导致最初的快速损失（小于 1 分钟），随后是较慢的释放，显示出简单的指数衰减。这些囊泡中较慢的 Ca2+损失的 t1/2 值分别为 16.1±0.9 分钟（主动加载，n = 5）和 18.4±0.9 分钟（被动加载，n = 3）。在含有 EGTA 和 A23187 的等渗介质中稀释会从这些加载的囊泡中释放所有螯合的 Ca2+。
