Nachshen D A, Blaustein M P
Department of Physiology, University of Maryland School of Medicine, Baltimore 21201, USA.
J Gen Physiol. 1980 Dec;76(6):709-28. doi: 10.1085/jgp.76.6.709.
Potassium-stimulated 45Ca entry into rat brain synaptosomes was measured at times ranging from 1 to 60 s. The K-rich solutions were used to depolarize the synaptosomes. Backflux of 45Ca from the synaptosomes was negligible during the first 10-20 s of incubation. An initial ("fast") phase of K-stimulated Ca entry, lasting from 1 to 2 s was observed. This phase was inhibited by low concentrations of La (KI approximately equal to 0.3 microM). It was also abolished ("inactivated") by incubating the synaptosomes in depolarizing solutions (containing veratridine, gramicidin, or elevated [K]o) before the addition of 45Ca. An additional long lasting ("slow") phase of K-stimulated Ca entry was also detected. This "slow" Ca entry was much less sensitive to La (KI > 100 microM) and was not affected by depolarizing the synaptosomes before the addition of 45Ca. The rate of influx during the fast phase was about four times the rate of Ca influx during the slow phase. Neither the fast nor slow phase of Ca entry was sensitive to tetrodotoxin (10 microM), a potent blocker of Na channels, but both phases were inhibited by Ni, Mn, Mg, and other agents that block Ca channels. The data are consistent with the presence of two distinct populations of voltage-regulated, divalent cation-selective pathways for Ca entry in presynaptic brain nerve endings.
在1至60秒的时间段内，测定了钾刺激的45Ca进入大鼠脑突触体的情况。用富含钾的溶液使突触体去极化。在孵育的最初10 - 20秒内，45Ca从突触体的反向通量可忽略不计。观察到钾刺激的钙进入有一个初始（“快速”）阶段，持续1至2秒。该阶段受到低浓度镧（KI约等于0.3 microM）的抑制。在添加45Ca之前，将突触体置于去极化溶液（含有藜芦碱、短杆菌肽或升高的[K]o）中孵育，该阶段也会被消除（“失活”）。还检测到钾刺激钙进入的另一个持久（“缓慢”）阶段。这种“缓慢”的钙进入对镧的敏感性要低得多（KI > 100 microM），并且在添加45Ca之前对突触体去极化不敏感。快速阶段的流入速率约为缓慢阶段钙流入速率的四倍。钙进入的快速阶段和缓慢阶段对河豚毒素（10 microM）均不敏感（河豚毒素是钠通道的有效阻滞剂），但两个阶段均受到镍、锰、镁和其他阻断钙通道的试剂的抑制。这些数据与在突触前脑神经末梢存在两种不同的电压调节二价阳离子选择性钙进入途径的情况一致。
