单价和二价阳离子对嗜铬细胞分泌膜囊泡跨膜钙离子通量的影响。

Effects of monovalent and divalent cations on Ca2+ fluxes across chromaffin secretory membrane vesicles.

作者信息

Krieger-Brauer H I, Gratzl M

出版信息

J Neurochem. 1983 Nov;41(5):1269-76. doi: 10.1111/j.1471-4159.1983.tb00821.x.

DOI:10.1111/j.1471-4159.1983.tb00821.x

Abstract

Bovine chromaffin secretory vesicle ghosts loaded with Na+ were found to take up Ca2+ when incubated in K+ media or in sucrose media containing micromolar concentrations of free Ca2+. Li+- or choline+-loaded ghosts did not take up Ca2+. The Ca2+ accumulated by Na+-loaded ghosts could be released by the Ca2+ ionophore A23187, but not by EGTA. Ca2+ uptake was inhibited by external Sr2+, Na+, Li+, or choline+. All the 45Ca2+ accumulated by Na+-dependent Ca2+ uptake could be released by external Na+, indicating that both Ca2+ influx and efflux occur in a Na+-dependent manner. Na+-dependent Ca2+ uptake and release were only slightly inhibited by Mg2+. In the presence of the Na+ ionophore Monensin the Ca2+ uptake by Na+-loaded ghosts was reduced. Ca2+ sequestered by the Na+-dependent mechanism could also be released by external Ca2+ or Sr2+ but not by Mg2+, indicating the presence of a Ca2+/Ca2+ exchange activity in secretory membrane vesicles. This Ca2+/Ca2+ exchange system is inhibited by Mg2+, but not by Sr2+. The Na+-dependent Ca2+ uptake system in the presence of Mg2+ is a saturable process with an apparent Km of 0.28 microM and a Vmax = 14.5 nmol X min-1 X mg protein-1. Ruthenium red inhibited neither the Na+/Ca2+ nor the Ca2+/Ca2+ exchange, even at high concentrations.

摘要

发现装载了Na⁺的牛嗜铬细胞分泌囊泡幽灵在K⁺培养基或含有微摩尔浓度游离Ca²⁺的蔗糖培养基中孵育时会摄取Ca²⁺。装载Li⁺或胆碱⁺的幽灵不摄取Ca²⁺。由装载Na⁺的幽灵积累的Ca²⁺可被Ca²⁺离子载体A23187释放，但不能被EGTA释放。Ca²⁺摄取受到外部Sr²⁺、Na⁺、Li⁺或胆碱⁺的抑制。通过Na⁺依赖性Ca²⁺摄取积累的所有⁴⁵Ca²⁺均可被外部Na⁺释放，这表明Ca²⁺的流入和流出均以Na⁺依赖性方式发生。Na⁺依赖性Ca²⁺摄取和释放仅受到Mg²⁺的轻微抑制。在存在Na⁺离子载体莫能菌素的情况下，装载Na⁺的幽灵对Ca²⁺的摄取减少。通过Na⁺依赖性机制螯合的Ca²⁺也可被外部Ca²⁺或Sr²⁺释放，但不能被Mg²⁺释放，这表明分泌膜囊泡中存在Ca²⁺/Ca²⁺交换活性。这种Ca²⁺/Ca²⁺交换系统受到Mg²⁺的抑制，但不受Sr²⁺的抑制。在存在Mg²⁺的情况下，Na⁺依赖性Ca²⁺摄取系统是一个可饱和的过程，其表观Km为0.28微摩尔，Vmax = 14.5纳摩尔×分钟⁻¹×毫克蛋白质⁻¹。钌红即使在高浓度下也不抑制Na⁺/Ca²⁺或Ca²⁺/Ca²⁺交换。