The effects of protons on 3',5'-cGMP-activated currents in photoreceptor patches.
Macroscopic 3',5'-guanine cyclic monophosphate (cGMP)-activated currents from photoreceptor outer segment membranes were examined as the pH on the cytoplasmic face of inside/out patches was reduced. In the absence of divalent cations, protons reduced the current in both directions without affecting the shape of the current-voltage relation consistent with a voltage-independent block. When Ca2+ was added to the bath, increasing the [H+] relieved the Ca2+ block and eliminated the Ca(2+)-induced reversal potential shifts seen at pH 7.4. These results suggest that protons alter Na+/Ca2+ permeability of the channel and relieve Ca2+ block of the sodium transport.
Tanaka
J C
JC
Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia 19104-6089.
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology; D002413:Cations, Divalent / Q000494:pharmacology; D006152:Cyclic GMP / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects; D010786:Photoreceptor Cells / Q000187:drug effects / Q000502:physiology; D011522:Protons; D011894:Rana pipiens; D012374:Rod Cell Outer Segment / Q000187:drug effects / Q000502:physiology*; D015222:Sodium Channels / Q000187:drug effects / Q000502:physiology
D015220:Calcium Channels; D002413:Cations, Divalent; D007473:Ion Channels; D011522:Protons; D015222:Sodium Channels; D006152:Cyclic GMP; D002118:Calcium