Relationship between light sensitivity and intracellular free Ca concentration in Limulus ventral photoreceptors. A quantitative study using Ca-selective microelectrodes.
Relationship between light sensitivity and intracellular free Ca concentration in Limulus ventral photoreceptors. A quantitative study using Ca-selective microelectrodes.
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DOI：
10.1085/jgp.85.6.805
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发表时间：
1985-06
期刊：
影响因子：
--
通讯作者：
Fein A
中科院分区：
文献类型：
--
作者：
Levy S;Fein A
钙离子在介导与光适应相关的灵敏度在鲎腹侧光感受器下降的可能作用进行了评估，通过同时测量光的敏感性和细胞内游离钙浓度（蔡），后者通过使用钙选择性微电极测量。在暗适应光感受器中，平均静息Cai为3.5 +/- 2.5 microM SD（n = 31）。静息Cai和细胞间绝对敏感性之间没有相关性。一般来说，光感受器对光线的敏感度并不一致，在均匀光照下，细胞最敏感区域（横纹肌叶）的Cai上升比远离它的区域大20-40倍，Cai上升速度也快20-40倍。在短暂的闪光中，当吸收10（2）个光子时，Cai上升几乎检测不到，当吸收大约10（5）个光子时，Cai上升达到饱和。在维持光照期间，从光适应阈值附近开始，稳定的Cai增加与几个对数单位的光强度的稳定脱敏相关：100倍脱敏与Cai增加2.5倍相关。在明亮的闪光之后，敏感性和Cai以不同的时间过程恢复：当Cai已经恢复到刺激前水平时，细胞仍然脱敏约0.5个对数单位，这表明在这些条件下Cai不是暗适应的限速步骤。EGTA的离子电泳注射显着降低光诱导的蔡上升，并增加了时间的光响应的峰值，但没有改变休息蔡，这表明，峰值的时间是由结合Ca 2+的能力的变化，而不是由休息蔡的影响。降低细胞外Ca 2+浓度（Cao）首先降低Cai，增加敏感性。较长时间暴露于低Cao导致Cai进一步降低，但敏感性降低而不是增加，这表明在某些条件下，Cai和敏感性是可能分离的。
The possible role of Ca ions in mediating the drop in sensitivity associated with light adaptation in Limulus ventral photoreceptors was assessed by simultaneously measuring the sensitivity to light and the intracellular free Ca concentration (Cai); the latter was measured by using Ca-selective microelectrodes. In dark-adapted photoreceptors, the mean resting Cai was 3.5 +/- 2.5 microM SD (n = 31). No correlation was found between resting Cai and absolute sensitivity from cell to cell. Typically, photoreceptors are not uniformly sensitive to light; the Cai rise evoked by uniform illumination was 20-40 times larger and faster in the most sensitive region of the cell (the rhabdomeral lobe) than it was away from it. In response to a brief flash, the Cai rise was barely detectable when 10(2) photons were absorbed, and it was saturated when approximately 10(5) photons were absorbed. During maintained illumination, starting near the threshold of light adaptation, steady Cai increases were associated with steady desensitizations over several log units of light intensity: a 100-fold desensitization was associated with a 2.5-fold increase in Cai. After a bright flash, sensitivity and Cai recovered with different time courses: the cell was still desensitized by approximately 0.5 log units when Cai had already recovered to the prestimulus level, which suggests that under those conditions Cai is not the rate-limiting step of dark adaptation. Ionophoretic injection of EGTA markedly decreased the light-induced Cai rise and increased the time to peak of the light response, but did not alter the resting Cai, which suggests that the time to peak is affected by a change in the capacity to bind Ca2+ and not by resting Cai. Lowering the extracellular Ca2+ concentration (Cao) first decreased Cai and increased sensitivity. Longer exposure to low Cao resulted in a further decrease of Cai but decreased rather than increased sensitivity, which suggests that under certain conditions it is possible to uncouple Cai and sensitivity.