Cervetto L, McNaughton P A
J Physiol. 1986 Jan;370:91-109. doi: 10.1113/jphysiol.1986.sp015924.
The light-sensitive current of isolated toad rods was recorded using the method of Yau, McNaughton & Hodgkin (1981) and the effects of the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX) and of La ions were examined. IBMX caused an increase in the light-sensitive current and a prolongation of the time course of the response. A small inward current which may reflect the operation of an Na-Ca exchange pump was also increased in IBMX. With low doses of IBMX the time course of the dim flash response could be mapped onto that in Ringer solution by a linear transformation of the time scale. Light adaptation had opposite effects to those of IBMX on the time course of the dim flash response, and a steady background light could exactly neutralize the effects of IBMX on the time course. Light adaptation had the additional effect of strongly reducing the amplitude of the dim flash response. La ions caused a rapid inhibition (t1/2 less than 1 s) followed by slow inhibition (t1/2 approximately equal to 30 s) of the light-sensitive current. In low [Ca] the rapid inhibition became more prominent, perhaps because of a competition between La and Ca for a blocking site near the light-sensitive channel. The time constants of the falling phases of responses to both bright and dim flashes were slowed by La. The dim flash response could be fitted by a model in which a single time constant in the chain underlying the flash response is slowed by La. La reduced the rate of activation of light-sensitive current in response to a reduction of external [Ca]. A concentration of La sufficient to block the activation of current in low [Ca] did not prevent the activation of current in IBMX. Light-sensitive currents carried by Mn, Ca or Mg in the absence of Na and in the presence of IBMX were inhibited by La. An outward current observed in the absence of permeable ions was inhibited by La. The effects of La on the time course of the response and on the rate of activation of current when [Ca] is reduced are consistent with an inhibition of the Ca pump. La ions also have a high affinity for the light-sensitive channel and can block current carried by another ion.
采用Yau、McNaughton和Hodgkin（1981年）的方法记录分离的蟾蜍视杆细胞的光敏电流，并研究磷酸二酯酶抑制剂3-异丁基-1-甲基黄嘌呤（IBMX）和镧离子的作用。IBMX使光敏电流增加，并使反应的时间进程延长。一种可能反映钠钙交换泵运作的小内向电流在IBMX中也增加了。使用低剂量的IBMX时，暗闪光反应的时间进程可以通过时间尺度的线性变换映射到林格氏液中的时间进程上。光适应对暗闪光反应的时间进程的影响与IBMX相反，稳定的背景光可以完全抵消IBMX对时间进程的影响。光适应还有强烈降低暗闪光反应幅度的额外作用。镧离子对光敏电流产生快速抑制（t1/2小于1秒），随后是缓慢抑制（t1/2约等于30秒）。在低[Ca]时，快速抑制变得更加明显，这可能是因为镧和钙在光敏通道附近的一个阻断位点存在竞争。镧使对明亮和暗闪光反应的下降阶段的时间常数减慢。暗闪光反应可以用一个模型来拟合，在该模型中，闪光反应基础链中的单个时间常数被镧减慢。镧降低了对外界[Ca]降低时光敏电流的激活速率。在低[Ca]中足以阻断电流激活的镧浓度并不能阻止在IBMX中电流的激活。在无钠且存在IBMX的情况下，由锰、钙或镁携带的光敏电流被镧抑制。在无通透离子时观察到的外向电流被镧抑制。镧对反应时间进程和[Ca]降低时电流激活速率的影响与对钙泵的抑制作用一致。镧离子对光敏通道也有高亲和力，并且可以阻断由另一种离子携带的电流。
