Cyclic GMP-sensitive conductance in outer segment membrane of catfish cones.
A cyclic GMP-sensitive conductance has recently been observed with patch-clamp recording in excised inside-out patches of plasma membrane from frog and toad rod outer segments. This conductance has properties suggesting that it is probably the light-sensitive conductance involved in visual transduction. We now report a similar conductance in the outer segment membrane of catfish cones. Cyclic GMP showed positive cooperativity in opening this conductance, with a Hill coefficient of 1.6-3.0 and a half-saturating cGMP concentration of 35-70 microM. Cyclic AMP at 1 mM, or changing Ca concentration (in the presence of Mg), had little effect on the conductance. In physiological solutions the cGMP-induced current had a reversal potential near +10 mV; the current amplitude increased roughly exponentially with membrane potential in both depolarizing and hyperpolarizing directions. Our results suggest that cGMP is also the internal transmitter for phototransduction in cones.
Haynes
L
L
Yau
K W
KW
D000818:Animals; D002462:Cell Membrane / Q000502:physiology; D006152:Cyclic GMP / Q000494:pharmacology / Q000502:physiology*; D004553:Electric Conductivity / Q000187:drug effects; D005399:Fishes; D008564:Membrane Potentials; D010775:Photic Stimulation; D010786:Photoreceptor Cells / Q000187:drug effects / Q000502:physiology*; D012374:Rod Cell Outer Segment / Q000502:physiology*; D014785:Vision, Ocular
D006152:Cyclic GMP