Baker P F, Glitsch H G
Philos Trans R Soc Lond B Biol Sci. 1975 Jun 10;270(908):389-409. doi: 10.1098/rstb.1975.0018.
Transmitter release from depolarized nerve terminals seems to be preceded by a rise in the intracellular concentration of ionized calcium. In squid giant axons, depolarization promotes calcium entry by two routes: one that is blocked by tetrodotoxin and one that is insensitive to tetrodotoxin. The TTX-sensitive route seems to be the sodium channel of the action potential; but the TTX-insensitive route seems to be quite distinct from the sodium and potassium channels of the action potential. It is blocked by Mg-2+, Mn-2+ and Co-2+ ions and by the organic calcium antagonist D-600 and has many features in common with the mechanism that couples excitation to secretion.
去极化神经末梢释放递质之前，细胞内游离钙的浓度似乎会升高。在枪乌贼的巨大轴突中，去极化通过两条途径促进钙内流：一条被河豚毒素阻断，另一条对河豚毒素不敏感。对河豚毒素敏感的途径似乎是动作电位的钠通道；但对河豚毒素不敏感的途径似乎与动作电位的钠通道和钾通道有很大不同。它被镁离子、锰离子和钴离子以及有机钙拮抗剂D - 600阻断，并且在许多方面与将兴奋与分泌相偶联的机制有共同之处。
