Haynes L, Yau K W
Nature. 1985;317(6032):61-4. doi: 10.1038/317061a0.
A cyclic GMP-sensitive conductance has recently been observed with patch-clamp recording in excised inside-out patches of plasma membrane from frog and toad rod outer segments. This conductance has properties suggesting that it is probably the light-sensitive conductance involved in visual transduction. We now report a similar conductance in the outer segment membrane of catfish cones. Cyclic GMP showed positive cooperativity in opening this conductance, with a Hill coefficient of 1.6-3.0 and a half-saturating cGMP concentration of 35-70 microM. Cyclic AMP at 1 mM, or changing Ca concentration (in the presence of Mg), had little effect on the conductance. In physiological solutions the cGMP-induced current had a reversal potential near +10 mV; the current amplitude increased roughly exponentially with membrane potential in both depolarizing and hyperpolarizing directions. Our results suggest that cGMP is also the internal transmitter for phototransduction in cones.
最近在青蛙和蟾蜍视杆细胞外段质膜的内向外膜片钳记录中观察到一种环鸟苷酸（cGMP）敏感电导。这种电导的特性表明它可能是视觉转导中涉及的光敏感电导。我们现在报告在鲶鱼视锥细胞外段膜中也存在类似的电导。环鸟苷酸在打开这种电导时表现出正协同性，希尔系数为1.6 - 3.0，半饱和cGMP浓度为35 - 70微摩尔。1毫摩尔的环腺苷酸（cAMP）或改变钙离子浓度（在存在镁离子的情况下）对该电导几乎没有影响。在生理溶液中，cGMP诱导的电流反转电位接近 +10毫伏；在去极化和超极化方向上，电流幅度大致随膜电位呈指数增加。我们的结果表明，cGMP也是视锥细胞光转导的胞内递质。
