Kometani T, Kasai M
J Membr Biol. 1980 Sep 30;56(2):159-68. doi: 10.1007/BF01875967.
The volume change of sarcoplasmic reticulum vesicles was induced by Ca2+ uptake. This volume change was measured by the light-scattering method. When vesicles were shrunk beforehand under the condition that anions are more permeable than cations, they swelled during Ca2+ uptake due to the concomitant incorporation of anions. On the contrary, they shrank with Ca2+ uptake due to the extrusion of cations under the condition that cations are more permeable than anions. From the analysis of the volume change it was concluded that all ions other than Ca2+ were transported passively in order to neutralize the membrane potential generated by the Ca2+ pump. These results support the idea that the Ca2+ pump is electrogenic. By using this technique, it became possible to measure the fast Ca2+ uptake rate. The dependence of the Ca2+ uptake rate on the Ca2+ concentration suggests that the site at which Ca2+ inhibits Ca2+ uptake is located inside the vesicle. From the osmotic response of the vesicles, the intravesicular concentration of free Ca2+ was estimated to be about 15 mM, when Ca2+ was fully taken up under the physiological condition.
肌浆网囊泡的体积变化是由钙离子摄取诱导的。这种体积变化通过光散射法进行测量。当囊泡在阴离子比阳离子更易通透的条件下预先收缩时，由于伴随阴离子的掺入，它们在钙离子摄取过程中会膨胀。相反，在阳离子比阴离子更易通透的条件下，它们会因阳离子的排出而在钙离子摄取时收缩。通过对体积变化的分析得出结论，除钙离子外的所有离子都是被动转运的，以中和由钙离子泵产生的膜电位。这些结果支持了钙离子泵是生电的这一观点。通过使用这种技术，得以测量快速的钙离子摄取速率。钙离子摄取速率对钙离子浓度的依赖性表明，钙离子抑制钙离子摄取的位点位于囊泡内部。根据囊泡的渗透反应，当在生理条件下钙离子被完全摄取时，囊泡内游离钙离子的浓度估计约为15 mM。
