Chinn K, Lisman J
J Gen Physiol. 1984 Sep;84(3):447-62. doi: 10.1085/jgp.84.3.447.
In addition to increasing the conductance to sodium, light reduces the maintained voltage-dependent potassium current (iK) in Limulus ventral photoreceptors. We have investigated the mechanism underlying this long-lasting decrease in ik. Intracellular injection of calcium produced a similar reduction of the voltage-dependent outward current. This reduction was not due to an activation of the voltage-dependent inward current (iin) because calcium injection reduced the outward current even under conditions where iin was blocked with Ni2+, and because calcium injection produced a decrease in conductance, as measured from the slope of the instantaneous i-V curve. The effect of light on ik could be blocked by injection of the calcium buffer EGTA (pCa 7.1) to an intracellular concentration of 50-70 mM. Even larger injections of the pH buffer MOPS (100-200 mM) did not reduce the effect of light on ik. These experiments show that intracellular free calcium (Cai2+) can reduce ik. Furthermore, since Cai2+ is known to increase in light, our results are consistent with the hypothesis that calcium is the internal transmitter for the light-induced decrease in ik.
除了增加对钠的电导外，光还会降低鲎腹侧光感受器中持续存在的电压依赖性钾电流（iK）。我们已经研究了iK这种长期下降背后的机制。细胞内注射钙会使电压依赖性外向电流产生类似的降低。这种降低并非由于电压依赖性内向电流（iin）的激活，因为即使在iin被Ni2+阻断的条件下，注射钙仍会降低外向电流，而且注射钙会导致电导降低，这是根据瞬时i-V曲线的斜率测量得出的。通过将钙缓冲剂EGTA（pCa 7.1）注射到细胞内浓度为50 - 70 mM，可以阻断光对iK的影响。即使注射更大剂量的pH缓冲剂MOPS（100 - 200 mM）也不会降低光对iK的影响。这些实验表明细胞内游离钙（Cai2+）可以降低iK。此外，由于已知Cai2+在光照下会增加，我们的结果与钙是光诱导iK降低的细胞内递质这一假设一致。
