MODULATION OF THE CGMP-ACTIVATED CONDUCTANCE OF THE PLASMA-MEMBRANE OF PHOTORECEPTOR CELLS BY CALMODULIN

The effect of calmodulin on the integral cGMP-activated conductance of ROS plasma membrane has been investigated by using the ''patch-clamp' ' techniques (inside-out configuration) Calmodulin increased the appar ent Michaelis constant (K-m) from 19+/-1.5 (in the absence of calmodul in) to 33.7+/-5.5 mM. However, it did not influence the Hill coefficie nt and the maximum conductance of cGMP-channels. Ca2+ ions were requir ed for the calmodulin effect (EC(50) = 452+/-47 nM). The results of ou r experiments with the use of 8-Br-cGMP and IBMX suggest that the modu lating action of calmodulin was not mediated by the ROS phosphodiester ase activation. The action of some calmodulin inhibitors has been test ed. On the basis of our study calmodulin is suggested to be very signi ficant for the recovery and light adaptation processes by changing the affinity of the cGMP-channel for agonist.