KINETICS OF PHOTOTRANSDUCTION IN RETINAL RODS OF THE NEWT TRITURUS-CRISTATUS
KINETICS OF PHOTOTRANSDUCTION IN RETINAL RODS OF THE NEWT TRITURUS-CRISTATUS
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DOI：
10.1113/jphysiol.1989.sp017873
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发表时间：
1989-12-01
影响因子：
5.5
通讯作者：
TORRE, V
中科院分区：
文献类型：
--
作者：
FORTI, S;MENINI, A;TORRE, V
用吸电极记录膜电流的方法，分析了蝾螈视网膜视杆细胞对闪光和阶跃光的光反应动力学。在暗适应条件下，在光开始后1 s的固定时间的光响应的归一化幅度与光强度之间的关系可以通过指数或多项式关系来拟合。在存在稳定的强光的情况下，同样的关系可以用米氏关系来拟合。光刺激的光响应动力学重建使用的模型中，其中：（i）三个分子的鸟苷3“，5”-环一磷酸（ii）光激活磷酸二酯酶，其水解环GMP，从而关闭光敏通道;（iii）Ca 2+离子渗透通过光敏通道;和（iv）胞内Ca 2+以协同方式抑制合成环GMP的酶环化酶。该模型再现了缩短的时间，从约1080毫秒到约690毫秒，更明亮的灯光短暂的闪光光响应的峰值。该模型还解释了在存在稳定光的情况下观察到的达到峰值的时间缩短到350 ms，以及在更亮的闪光下缺乏进一步的加速。在模型中的细胞内钙缓冲的存在下帐户的光电流的部分再激活后，光的一个步骤，持续几秒钟。这种再激活的时间过程在实验和模型中都没有被稳定的强光加速。在消光到长的光阶跃后，光电流显示出快速的部分再活化，随后是光响应的缓慢组分，其以约0.05 s-1的速率常数熄灭。该模型解释了这一缓慢的组成部分的起源，假设激活视紫红质的失活是部分可逆的。该模型还能够解释当将不同量的外源性钙缓冲剂掺入到杆中时的特定动力学变化（Torre，马修斯和Lamb，1986）。
The kinetics of photoresponses to flashes and steps of light of rods, from the retina of the newt Triturus cristatus, were analysed by recording the membrane current with a suction electrode. In dark-adapted conditions the relation between the normalized amplitude of the photoresponse at a fixed time 1 s after the onset of light and the light intensity could be fitted by an exponential or a polynomial relation. In the presence of a steady bright light the same relation could be fitted by a Michaelis-Menten relation. The kinetics of photoresponses to light stimuli were reconstructed using a model in which: (i) three molecules of guanosine 3'',5''-cyclic monophosphate (cyclic GMP) open a light-sensitive channel; (ii) light activates the enzyme phosphodiesterase, which hydrolyses cyclic GMP, thus closing light-sensitive channels; (iii) Ca2+ ions permeate through light-sensitive channels; and (iv) intracellular Ca2+ inhibits, in a co-operative way, the enzyme cyclase, which synthesizes cyclic GMP. The model reproduces the shortening of the time to peak of brief flash photoresponses from about 1080 ms to about 690 ms with brighter lights. The model also explains the shortening of the time to peak to 350 ms observed in the presence of a steady light and the lack of a further acceleration with brighter flashes of lights. The presence in the model of an intracellular calcium buffer accounts for the partial reactivation of the photocurrent following a step of light, lasting several seconds. The time course of this reactivation is not accelerated by a steady bright light both experimentally and in the model. After the extinction to a long step of light the photocurrent showed a rapid partial reactivation, which was followed by a slow component of the photoresponse which extinguished with a rate constant of about 0.05 s-1. The model exlains the origin of this slow component by assuming that the inactivation of excited rhodopsin is partially reversible. The model is also able to explain the particular chnges of kinetics when different amounts of exogenous calcium buffers are incorporated into rods (Torre, Matthews and Lamb, 1986).