Van Breemen C, Daniel E E, Van Breemen D
J Gen Physiol. 1966 Jul;49(6):1265-97. doi: 10.1085/jgp.0491265.
The calcium content and distribution of the rat uterus were determined employing flame photometry and Ca determinations. The total uterine calcium concentration was found to be 2.25 millimoles (mmoles) per kilogram wet weight, 0.45 of which was inexchangeable. The exchangeable Ca could be divided into 0.8 mmole/kg wet weight extracellular and 1.0 mmole/kg wet weight intracellular. The concentration of ionic Ca in rat serum was obtained by equilibrium dialysis as 1.5 mM or 53 % of the total serum Ca. The observed Ca distribution required that its active transport be postulated, since the membrane was shown to be permeable to Ca and the internal Ca concentration was far below its electrochemical equilibrium value. Metabolic inhibition by iodoacetate or dinitrophenol caused a net Ca uptake, but cooling to 4°C and ouabain did not. Iodoacetate did not affect the Ca efflux, but did increase the influx, suggesting that active Ca transport is accomplished by an exclusion mechanism. In experiments with varied external sodium concentrations, no evidence was obtained that sodium competes with calcium for inward transport. Cellular Ca binding was measured under conditions of prolonged metabolic inhibition, which abolished both active transport and the membrane potential. The association constants obtained were compatible with intracellular Ca binding to proteins, but insufficient to account for the low level of intracellular ionic Ca believed essential for relaxation. Hence metabolically dependent intracellular Ca binding was postulated. The Ca efflux was slowed down by Ca-free efflux media. The presence of Sr or EDTA could completely prevent this decrease in efflux rate, and Ba could partly prevent it. Changes in Mg and Na concentration did not affect the rate of Ca efflux. A model to explain Ca exchange across smooth muscle membranes has been proposed.
采用火焰光度法和钙测定法测定了大鼠子宫的钙含量和分布。发现子宫总钙浓度为每千克湿重2.25毫摩尔（mmol），其中0.45为不可交换钙。可交换钙可分为细胞外0.8 mmol/kg湿重和细胞内1.0 mmol/kg湿重。通过平衡透析测得大鼠血清中离子钙浓度为1.5 mM，占血清总钙的53%。观察到的钙分布情况表明需要假定其存在主动转运，因为已证明细胞膜对钙具有通透性，而细胞内钙浓度远低于其电化学平衡值。碘乙酸或二硝基酚引起的代谢抑制导致净钙摄取，但冷却至4°C和哇巴因则不会。碘乙酸不影响钙外流，但会增加钙内流，这表明钙的主动转运是通过一种排阻机制完成的。在不同外部钠浓度的实验中，未获得钠与钙竞争内向转运的证据。在长期代谢抑制的条件下测量了细胞钙结合情况，这种抑制消除了主动转运和膜电位。得到的结合常数与细胞内钙与蛋白质的结合情况相符，但不足以解释据信对舒张至关重要的低水平细胞内离子钙。因此假定存在代谢依赖性细胞内钙结合。无钙外流培养基使钙外流减慢。锶或乙二胺四乙酸（EDTA）的存在可完全阻止外流速率的这种降低，钡可部分阻止。镁和钠浓度的变化不影响钙外流速率。已提出一个解释钙在平滑肌膜上交换的模型。
