Photosensitivity of 8BrcGMP-induced conductance in ROS-excised patches

Inside-out patches from ROS plasma membranes contain the basic enzymes of the phototransduction cascade. Similar to a native photoreceptor cell, such patches are capable of responding to light, the effect of which suppresses the cGMP-activated current. Photoresponses are observed only in the presence of GTP, whereas ATP essentially accelerates the current recovery to a dark level. Photoresponses are also observed in the presence of 8BrcGMP. Phosphodiesterase (PDE) hydrolyzes 8BrcGMP two orders of magnitude slower than cGMP, so the light inhibition of the 8BrcGMP-induced current cannot be accounted for by PDE activation. It seems that activity of cGMP-gated channels depends not only on cGMP concentration, but is additionally controlled by some other regulatory mechanisms.