Cyclic GMP-sensitive conductance of retinal rods consists of aqueous pores.
The surface membrane of retinal rod and cone outer segments contains a cation-selective conductance which is activated by 3',5'-cyclic guanosine monophosphate (cGMP). Reduction of this conductance by a light-induced decrease in the cytoplasmic concentration of cGMP appears to generate the electrical response to light, but little is known about the molecular nature of the conductance. The estimated unitary conductance is so small that ion transport might occur via either a carrier or a pore mechanism. Here we report recordings of cGMP-activated single-channel currents from excised rod outer segment patches bathed in solutions low in divalent cations. Two elementary conductances, of approximately 24 and 8 pS, were observed. These conductances are too large to be accounted for by carrier transport, indicating that the cGMP-activated conductance consists of aqueous pores. The dependence of the channel activation on the concentration of cGMP suggests that opening of the pore is triggered by cooperative binding of at least three cGMP molecules.
A L
AL
Zimmerman
D A
DA
Baylor
D000818:Animals; D006152:Cyclic GMP / Q000494:pharmacology*; D004553:Electric Conductivity; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects; D010786:Photoreceptor Cells / Q000502:physiology*; D012374:Rod Cell Outer Segment / Q000187:drug effects / Q000502:physiology*; D014562:Caudata
D007473:Ion Channels; D006152:Cyclic GMP