title: Protons block the dark current of isolated retinal rods.
abstract: Membrane currents of isolated frog rods were recorded with the suction pipette technique and tested by perfusion techniques for their sensitivity to H+. The following facts have been established. (i) Increased [H+] suppresses the Na+ conductance of the outer segment rapidly and reversibly. (ii) H+ acts in the rod interior. (iii) The [H+] necessary to cause a 50% decrement in Na+ conductance is inversely related to the [Ca2+] over 5 orders of magnitude. (iv) The sensitivity to H+ and the sensitivity to light, as a function of [Ca2+], have the same slope. Thus, H+ act like light in effecting membrane current suppression but behave as if their effect is mediated through Ca2+. Based on these results and properties of rod disk membrane phosphodiesterase, we propose that protons produced in the light-activated hydrolysis of cGMP liberate Ca2+ from the disks by ion exchange.
mesh_terms: D015106:3',5'-Cyclic-GMP Phosphodiesterases / Q000378:metabolism; D000818:Animals; D002118:Calcium; D003624:Darkness; D006863:Hydrogen-Ion Concentration; D007473:Ion Channels / Q000502:physiology; D010786:Photoreceptor Cells / Q000502:physiology*; D011522:Protons; D011894:Rana pipiens; D012374:Rod Cell Outer Segment / Q000502:physiology*; D012964:Sodium / Q000502:physiology; D014785:Vision, Ocular
chemical_list: D007473:Ion Channels; D011522:Protons; D012964:Sodium; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D002118:Calcium