细胞内外钙离子浓度对鲎腹神经感光器光适应的影响

THE INFLUENCE OF EXTRA AND INTRACELLULAR CALCIUM ON THEADAPTATION OF Limulus polyphemus VENTRAL NERVE PHOTORECEPTORS

用细胞内记录的方法研究了由微弱持续光刺激（６×１０６～９×１０６光子／ｃｍ２，１０ｓ）引起鲎（Ｌｉｍｕｌｕｓｐｏｌｙｐｈｅｍｕｓ）腹神经感光器膜电流的变化———光碰击。结果表明，在生理盐水（１０ｍｍｏｌ／ＬＣａ２＋）中光碰击的平均面积为（３９５±１７６）ｐＣ，微弱光适应（记录前２５ｓ加１次光闪，９×１０９光子／ｃｍ２）使得光碰击的面积下降至（１０５±２２９）ｐＣ（ｎ＝４）。在低钙溶液（０２５ｍｍｏｌ／ＬＣａ２＋）中，光适应的作用没有减弱，这次光闪使得平均的光碰击面积从（９２±１８７）ｐＣ下降到（２９±３０４）ｐＣ。为了消耗细胞内储存的钙离子，在低钙溶液中对感光器进行几次强光刺激（６４×１０１４光子／ｃｍ２），这时由２５ｓ前光闪引起的光适应现象减弱，光碰击的平均面积从（８１±１２９）ｐＣ降到（４１±３７４）ｐＣ。把１２ｍｍｏｌ／ＬＥＧＴＡ注入到浸浴在生理盐水中的感光器后，２５ｓ前光闪造成的光适应现象消失。实验结果说明，光刺激使得钙离子从存储器中释放出来，造成细胞内钙离子浓度上升，决定了感光器的光适应程度。

In physiological (10 mmol/L Ca 2+ )or low calcium saline (0 25 mmol/L Ca 2+ ) bumps were evoked by dim continuous light (6×10 6～9×10 6 photons/cm 2; 10 s) in Limulus polyphemus ventral nerve photoreceptors. The photoreceptor was dark adapted or weakly light adapted by a 0 5 ms conditioning flash (9×10 9 photons/cm 2), 2 5 s prior to the continuous illumination. In 10 mmol/L external calcium the mean size (current time integral)of the bumps was(39 5±1 76)pC; the light adaptation caused a decrease to (10 5±2 29)pC ( n =4). In low calcium saline the effect of light adaptation was not reduced. The conditioning flash caused a reduction of the average bump size from(92±18 7)pC to(29±3 04)pC. However, when in low calcium saline the photoreceptors were stimulated by a few strong flashes(6 4×10 14 photons/cm 2) in order to exhaust the intracellular calcium stores, the effect of light adaptation by the conditioning flash was reduced. The light adaptation caused a reduction of the bump size from(81±10 1)pC to(41±3 74)pC. Injection of 1 2 mmol/L EGTA into the dark adapted photoreceptors which were soaked by physiological saline almost abolished the effect of the light adaptation Thus, we conclude that the illumination releases calcium from the organelles. The changes of the cytosolic calcium concentration decides the degree of the light adaptation of the photoreceptors.