Single-channel study of the cGMP-dependent conductance of retinal rods from incorporation of native vesicles into planar lipid bilayers.
Unitary currents through cGMP-dependent channels of retinal rods are observed following incorporation into planar lipid bilayers of native vesicles from purified rod outer segment membranes washed free of soluble and peripheral proteins. The influence of the concentration of cGMP, inhibitors (cis-diltiazem, tetracaine and Ag+) and divalent cations (Ca2+, Mg2+, and Co2+) on the conductance and open probability of the channel is described, as well as the voltage dependence of these effects. The cGMP dependence suggests the existence of four binding sites for cGMP and reveals that sequential binding of four cGMP molecules corresponds to the opening of four discrete conductance levels. Finally, we provide conclusive evidence that activated G-protein does not directly inactivate the cGMP-dependent channels of bovine retinal rods.
Ildefonse
M
M
Unité de Recherche Associée 520 du Centre National de la Recherche Scientifique, Centre d'Etudes Nucléaires de Grenoble, France.
Bennett
N
N
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002417:Cattle; D003035:Cobalt / Q000494:pharmacology; D006152:Cyclic GMP / Q000494:pharmacology*; D004110:Diltiazem / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004553:Electric Conductivity / Q000187:drug effects / Q000502:physiology; D019204:GTP-Binding Proteins / Q000502:physiology; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D008051:Lipid Bilayers / Q000378:metabolism*; D008274:Magnesium / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D010786:Photoreceptor Cells / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D012834:Silver / Q000494:pharmacology; D013748:Tetracaine / Q000494:pharmacology
D007473:Ion Channels; D008051:Lipid Bilayers; D013748:Tetracaine; D003035:Cobalt; D012834:Silver; D019204:GTP-Binding Proteins; D004110:Diltiazem; D006152:Cyclic GMP; D008274:Magnesium; D002118:Calcium