CONTROL OF LIGHT-SENSITIVE CURRENT IN SALAMANDER RODS
CONTROL OF LIGHT-SENSITIVE CURRENT IN SALAMANDER RODS
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DOI：
10.1113/jphysiol.1988.sp017258
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发表时间：
1988-09-01
影响因子：
5.5
通讯作者：
NUNN, BJ
中科院分区：
文献类型：
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作者：
HODGKIN, AL;NUNN, BJ
1. 在Ca2+存在下，从Na+切换到Li+后光敏电流的指数下降可能取决于水解环GMP的磷酸二酯酶（PDE）的活性。2. 这种可能性得到了吸力电极实验的支持，该实验表明，在蟾蜍和蝾螈杆中，中等光照强度下电流的暴露衰减速率常数b增加了至少10倍，而在PDE抑制剂3-异丁基-1-甲基黄嘌呤（IBMX）的作用下电流的暴露衰减速率常数b降低了约10倍。3. 速率常数b对弱光或IBMX的敏感性约为膜电流的3倍。这可能是由钙离子的反馈所解释的，钙离子倾向于保持电流恒定，可能是通过钙抑制鸟苷酸环化酶。4. b的时间过程可能代表PDE活性的变化，通过在闪烁后的不同时间从Na+切换到Li+来测量。结果表明，中等强度的闪光（140 Rh*）在0.5 s内使b增加约7倍，之后b以1.5 ~ 2 s的时间常数下降。参数b的外推值表明，强闪光（5000-10,000 Rh*）使b从黑暗中的1 s-1增加到大约60 s-1，并且在电流达到饱和后，b继续随着闪光强度增加几个对数单位。6. 4和5中的观察结果很好地符合b与PDE活动有关的想法，后者的变化足以解释闪光响应的上升阶段。7. 闪光后，光敏电流比时间常数b-1恢复得快得多，如果闪光导致鸟苷酸环化酶活性的延迟增加，就可以解释这种差异。8. 环化酶激活的明显延迟增加与[Ca2+]i的抑制作用是一致的，当钙在反应的平台期被泵出时，抑制作用就会降低。9. 在闪光反应期间不同时间施加IBMX脉冲的实验支持闪光导致环状GMP供应速率延迟增加的观点。用IBMX对这些试验和其他试验进行定量分析，得到的速率常数与用Na+ .fwdarw得到的速率常数相似。李+方法。
1. The exponential decline of light-sensitive current seen after a switch from Na+ to Li+ in the presence of Ca2+ probably depends on the activity of the phosphodiesterase (PDE) which hydrolyses cyclic GMP. 2. This probability is supported by experiments with suction electrodes which show that in toad and salamander rods the rate constant, b, of the expoential decline of current was increased at least 10-fold by moderate light intensities and decreased about 10-fold by 3-isobutyl-1-methylxanthine (IBMX), an inhibitor of PDE. 3. The rate constant b is about 3 times more sensitive to weak lights or to IBMX than the membrane current. This may be explained by a feed-back involving calcium ions which tends to hold current constant, perhaps by calcium inhibition of guanylate cyclase. 4. The time course of b, which probably represents the changes in PDE activity, was measured by switching from Na+ to Li+ at various times after a flash. The results suggest that a moderate flash (140 Rh*) increased b about 7 times in 0.5 s and that b then declined with a time constant of 1.5-2 s. 5. Extrapolated values of the parameter b suggest that strong flashes (5000-10,000 Rh*) increased b from 1 s-1 in the dark to perhaps 60 s-1 and that b continued to increase with flash strength for several log units after the current had reached saturation. 6. The observations in 4 and 5 fit well with the idea that b is related to PDE activity and that changes in the latter are sufficient to account for the rising phase of the flash response. 7. After a flash the light-sensitive current recovers much more rapidly than the time constant b-1, a discrepancy which is explained if a light flash causes a delayed increase in guanylate cyclase activity. 8. The apparent delayed increase in cyclase activation is consistent with an inhibitory effect of [Ca2+]i which is reduced when calcium is pumped out during the plateau of the response. 9. Experiments in which pulses of IBMX were applied at different times during a flash response support the idea that a flash causes a delayed increase in the rate of supply of cyclic GMP. Quantitative analysis of these and other tests with IBMX gave rate constants similar to those obtained by the Na+ .fwdarw. Li+ method.