Calcium channel block by cadmium in chicken sensory neurons.
Cadmium block of calcium channels was studied in chicken dorsal root ganglion cells by a whole-cell patch clamp that provides high time resolution. Barium ion was the current carrier, and the channel type studied had a high threshold of activation and fast deactivation (type FD). Block of these channels by 20 microM external Cd2+ is voltage dependent. Cd2+ ions can be cleared from blocked channels by stepping the membrane voltage (Vm) to a negative value. Clearing the channels is progressively faster and more complete as Vm is made more negative. Once cleared of Cd2+, the channels conduct transiently on reopening but reequilibrate with Cd2+ and become blocked within a few milliseconds. Cd2+ equilibrates much more slowly with closed channels, but at a holding potential of -80 mV virtually all channels are blocked at equilibrium. Cd2+ does not slow closing of the channels, as would be expected if it were necessary for Cd2+ to leave the channels before closing occurred. Instead, the data show unambiguously that the channel gate can close when the channel is Cd2+ occupied.
Swandulla
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Department of Physiology, University of Pennsylvania, School of Medicine, Philadelphia 19104.
Armstrong
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D000818:Animals; D001464:Barium / Q000494:pharmacology; D002104:Cadmium / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D002645:Chickens; D004533:Egtazic Acid / Q000494:pharmacology; D005727:Ganglia, Spinal / Q000502:physiology; D008274:Magnesium / Q000494:pharmacology; D008536:Meglumine / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D009475:Neurons, Afferent / Q000187:drug effects / Q000502:physiology*; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D015220:Calcium Channels; D013757:Tetraethylammonium Compounds; D002104:Cadmium; D001464:Barium; D004533:Egtazic Acid; D019789:Tetraethylammonium; D008536:Meglumine; D008274:Magnesium