Modulation of rod, but not cone, cGMP-gated photoreceptor channels by calcium-calmodulin
Modulation of rod, but not cone, cGMP-gated photoreceptor channels by calcium-calmodulin
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DOI：
10.1017/s0952523800011378
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发表时间：
1997-03-01
影响因子：
1.9
通讯作者：
Stotz, SC
中科院分区：
文献类型：
--
作者：
Haynes, LW;Stotz, SC
从鲶鱼杆或锥体外段切除含有cgmp门控通道的内向外斑块，并置于电压钳下。测量饱和和过饱和cGMP浓度在+/-30 mV下引起的cGMP净依赖电流，并确定电流与cGMP浓度的依赖关系。用希尔方程拟合这些数据，估计了通道对其配体的表观亲和力。在+30 mV下，杆状通道和锥状通道中提供一半最大电流（K-1/2）所需的cGMP浓度分别与28 μ M和37 μ M相似，并且与电压依赖性较弱。因此，锥通道具有本质上比杆通道高的K-1/2。两种渠道的希尔系数均接近于2.3。在钙调蛋白存在下，杆状通道对cGMP的表观亲和力降低了约2倍，而锥状通道的表观亲和力未受影响。这些结果表明，钙调蛋白不能调节其配体的锥通道打开概率。这代表了光导机制中杆状和锥状光感受器之间的第一个显著差异，并表明锥状通道的β亚基一定不同于杆状通道的β亚基。
Inside-out patches containing cGMP-gated channels were excised from catfish rod or cone outer segments and held under voltage clamp. The net cGMP-dependent currents elicited by saturating and subsaturating concentrations of cGMP at +/-30 mV were measured and the dependence of current upon cGMP concentration was determined. The apparent affinity of the channel for its ligand was estimated by fitting these data with the Hill equation. The concentration of cGMP required to give half the maximum current (K-1/2) in rod and cone channels at +30 mV was similar to 28 mu M and similar to 37 mu M, respectively, and was weakly voltage dependent. Thus, cone channels have an intrinsically higher K-1/2 than rod channels. For both types of channel, the Hill coefficient was similar to 2.3. In the presence of calcium-calmodulin, the apparent affinity of the rod channel for cGMP decreased by about twofold, but the apparent affinity of the cone channels was unaffected. These results indicate that the open probability of the cone channel for its ligand cannot be modulated by calmodulin. This represents the first significant departure between rod and cone photoreceptors in mechanisms used by phototransduction and suggests that the beta subunit of the cone channel must be different from that of the rod channel.