不同钙离子浓度对鲎腹神经光感受器二种光碰击的影响

THE EFFECTS OF DIFFERENT CALCIUM CONCENTRATION ON THE TWO TYPES OF BUMPS IN LIMULUS POLYPHEMUS VENTRAL PHOTORECEPTORS

在生理盐水中用持续的弱光（６×１０６～９×１０６个光子／ｃｍ２）刺激鲎的腹神经光感受器细胞可得到二种类型的碰击，一种称谓“标准光碰击”或“Ｃ２碰击”，它有对称的形状，信号衰退的指数常数（λ）大于００１／毫秒。第二种光碰击是“小且慢光碰击”或“Ｃ１碰击”，它的平均振幅小于１００ｐＡ，信号衰退较慢，λ小于００１／毫秒。用“形态商数”，即碰击的振幅除半宽度（Ｔｈ／Ａ）可在计算机上把这两种光碰击较容易地区别。Ｃ２碰击的商数小于０５毫秒／ｐＡ，而Ｃ１碰击的商数大于１毫秒／ｐＡ。在低钙离子溶液中，Ｃ２碰击的振幅增加了１９０％。向细胞内注入微量１２ｍｍｏｌ／Ｌ钙离子螯合剂（ＥＧＴＡ），可减小Ｃ２碰击的振幅５０％以上，而且产生的频率也明显下降。但是，在同样的条件下，Ｃ１碰击的振幅和频率没有明显的改变。

Dark adapted ventral nerve photoreceptors of Limulus polyphemus were continuously illuminated with dim light and produced two types of bumps in saline containing 10 mmol/L calcium. One type of bumps was called “standard bump” or “C2 bump” which had a symmetrical form with fast rise and decay kinetics. The other type of bumps was called “small and slow bump”or “C1 bump” which had a small amplitude and slower kinetics. The half width of a bump divided by its amplitude (Th/Jmax=ms/pA) was found to be a reliable criterion to distinguish between the bumps. This shape quotient is never larger than 0 5 ms/pA in the “C2 bump” and is larger than 1 ms/pA in the “C1 bump”. When the calcium concentration in the superfusate was lowered to 0 25 mmol/L, the average amplitude of C2 bump rose to 190%. Pressure injection of 1 2 mmol/L EGTA saline into the photoreceptor cell reduced the average amplitude of C2 bump about 50% and the average frequency of the bump was also reduced. The average amplitude and frequency of C1 bump, however, was not significantly influenced. Our results confirm the assumption that these two types of bumps are generated by different light activated mechanisms that are differentially sensitive to changes of the cytosolic calcium concentration.