Uptake and release of 45Ca by Myxicola axoplasm.
Uptake and release of 45Ca by Myxicola axoplasm.
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DOI：
10.1085/jgp.78.4.413
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发表时间：
1981-10
期刊：
影响因子：
--
通讯作者：
Livengood D
中科院分区：
文献类型：
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作者：
Abercrombie RF;Masukawa LM;Sjodin RA;Livengood D
检查了从 Myxicola 巨轴突中分离出的轴浆对 45Ca 的结合和释放。观察到两种不同的结合成分，一种需要 ATP，一种不需要 ATP。添加线粒体抑制剂很大程度上阻止了 ATP 依赖性结合，而 ATP 独立成分则不受这些抑制剂的影响。在含有离子化 [Ca2+] = 0.54 microM 的溶液中，不依赖 ATP 的结合约占总 45Ca 吸收的三分之二，也是本次研究的主要焦点。这部分结合的 45Ca 以随培养液中 Ca2+ 浓度增加而增加的速率从轴浆中释放。离子 Cd2+ 和 Mn2+ 也能够增加样品中的 45Ca 流出量，但 Co2+、Ni2+、Mg2+ 和 Ba2+ 没有效果。 45Ca流出速率系数与浴液中Ca2+、Cd2+和Mn2+浓度的浓度响应曲线呈S形。添加饱和浓度的第二种离子不能超过由这些二价离子之一引起的最大流出速率。将浴液中的 EGTA 浓度从 100 µM 增加到 200 µM 并不会增加 45Ca 流出；然而，将摄取培养基中 EGTA 缓冲液的浓度从 100 µM 增加到 200 µM，并保持离子化 Ca2+ 恒定，导致更多的 45Ca 被轴浆结合。这些结果表明，Myxicola 轴浆中存在高亲和力、不依赖 ATP 的 45Ca 结合位点，可与 100 microM EGTA 竞争。 45Ca 流出结果根据与 Ca2+、Cd2+ 或 Mn2+ 相互作用的内源位点进行解释。
The binding and release of 45Ca by axoplasm isolated from Myxicola giant axons were examined. Two distinct components of binding were observed, one requiring ATP and one not requiring ATP. The ATP- dependent binding was largely prevented by the addition of mitochondrial inhibitors, whereas the ATP-independent component was unaffected by these inhibitors. The ATP-independent binding accounted for roughly two-thirds of the total 45Ca uptake in solutions containing an ionized [Ca2+] = 0.54 microM and was the major focus of this investigation. This fraction of bound 45Ca was released from the axoplasm at a rate that increased with increasing concentrations of Ca2+ in the incubation fluid. The ions Cd2+ and Mn2+ were also able to increase 45Ca efflux from the sample, but Co2+, Ni2+, Mg2+, and Ba2+ had no effect. The concentration-response curves relating the 45Ca efflux rate coefficients to the concentration of Ca2+, Cd2+, and Mn2+ in the bathing solution were S-shaped. The maximum rate of efflux elicited by one of these divalent ions could not be exceeded by adding a saturating concentration of a second ion. Increasing EGTA concentration in the bath medium from 100 to 200 microM did not increase 45Ca efflux; yet increasing the concentration of the EGTA buffer in the uptake medium from 100 to 200 microM and keeping ionized Ca2+ constant caused more 45Ca to be bound by the axoplasm. These results suggest the existence of high-affinity, ATP-independent binding sites for 45Ca in Myxicola axoplasm that compete favorably with 100 microM EGTA. The 45Ca efflux results are interpreted in terms of endogenous sites that interact with Ca2+, Cd2+, or Mn2+.