Bittner M A, Holz R W
Department of Pharmacology, University of Michigan Medical School, Ann Arbor 48109-0626.
J Biol Chem. 1992 Aug 15;267(23):16219-25.
We have determined that there are components to the time course of Ca(2+)-dependent secretion from digitonin-permeabilized bovine adrenal chromaffin cells that can be distinguished by Ca2+ sensitivity and ATP dependence. The effects of various Ca2+ concentrations are different on the initial rates and later rates of secretion. The earliest rates (5 s) are half-maximal between 30-100 microM Ca2+ and maximal by 300 microM Ca2+. Later rates of secretion are maximal by 10 microM and decline above 30 microM Ca2+. At low Ca2+ concentrations secretion begins after a lag of several seconds. The early rates of secretion (within 1 min) are dependent on the prior effects of MgATP. MgATP primes the cells to secrete. Later rates require the continuous presence of MgATP for optimal secretion. Incubation with low concentrations of Ca2+ increases the ability of MgATP to stimulate subsequent Ca(2+)-dependent secretion. Preincubation with Ca2+ has no effect on the rapid loss of ATP-independent secretion with time after permeabilization. The data indicate that: 1) as secretion progresses in digitonin-permeabilized cells, different events become rate-limiting; 2) maximal secretion at the early times requires at least 10-fold higher Ca2+ concentrations than at later times; 3) the rate at which Ca2+ initiates secretion is concentration-dependent; and 4) Ca2+ not only triggers the final events in secretion but enhances the ability of ATP to prime secretion.
我们已经确定，从洋地黄皂苷通透的牛肾上腺嗜铬细胞中进行的钙依赖分泌的时间进程存在不同组分，这些组分可通过钙敏感性和ATP依赖性来区分。不同钙浓度对分泌的初始速率和后期速率的影响不同。最早的速率（5秒）在30 - 100微摩尔/升钙时达到半最大，在300微摩尔/升钙时达到最大。后期分泌速率在10微摩尔/升时达到最大，在钙浓度高于30微摩尔/升时下降。在低钙浓度下，分泌在延迟几秒后开始。早期分泌速率（1分钟内）依赖于MgATP的先前作用。MgATP使细胞做好分泌准备。后期速率需要持续存在MgATP以实现最佳分泌。用低浓度钙孵育可增强MgATP刺激后续钙依赖分泌的能力。用钙预孵育对通透后ATP非依赖性分泌随时间的快速丧失没有影响。数据表明：1）随着洋地黄皂苷通透细胞中的分泌过程推进，不同事件成为限速因素；2）早期最大分泌所需的钙浓度比后期至少高10倍；3）钙引发分泌的速率是浓度依赖性的；4）钙不仅触发分泌的最终事件，还增强ATP引发分泌的能力。
