MODULATION OF THE CGMP-ACTIVATED CONDUCTA NCE OF ROS PLASMA-MEMBRANE BY CALMODULIN

The effect of calmodulin on the integral cGMP-activated conductance of ROS plasma membrane has been investigated using the <<patch-clamp>> t echnique (inside-out configuration). The apparent Michaelis constant ( K-m) and Hill coefficient of the cGMP-activated channel (cGMP-channel) well estimated in absence of calmodulin (19 +/- 1.5 mu M and 2.5 +/- 0.6, respectively). Calmodulin increased K-m to 33.7 +/- 5.5 mu M, how ever, it produced no effect on Hill coefficient and the maximum conduc tance of the cGMP-channels. Ca2+ ions were required for the effect of calmodulin (EC(50) = 452 +/- 47 nM). IBMX and replacement cGMP with 8- Br-cGMP did not abolish the effect of calmodulin. Calmodulin is sugges ted to play an important role in photorecovery and light adaptation pr ocesses by changing the affinity of the cGMP-channels for agonists.