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 segments1,2. This conductance has properties suggesting that it is probably the light-sensitive conductance involved in visual transduction1,2. We now report a similar conductance in the outer segment membrane of catfish cones. Cyclic GMP showed positive cooperatively in opening this conductance, with a Hill coefficient of 1.6-3.0 and a half-saturating cGMP concentration of 35-70 μM. 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.
|Original language||English (US)|
|Number of pages||4|
|State||Published - Dec 1 1985|
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