title: Delayed-rectifier K channels contribute to contrast adaptation in mammalian retinal ganglion cells.
abstract: Retinal ganglion cells adapt by reducing their sensitivity during periods of high contrast. Contrast adaptation in the firing response depends on both presynaptic and intrinsic mechanisms. Here, we investigated intrinsic mechanisms for contrast adaptation in OFF Alpha ganglion cells in the in vitro guinea pig retina. Using either visual stimulation or current injection, we show that brief depolarization evoked spiking and suppressed firing during subsequent depolarization. The suppression could be explained by Na channel inactivation, as shown in salamander cells. However, brief hyperpolarization in the physiological range (5-10 mV) also suppressed firing during subsequent depolarization. This suppression was selectively sensitive to blockers of delayed-rectifier K channels (K(DR)). In somatic membrane patches, we observed tetraethylammonium-sensitive K(DR) currents that activated near -25 mV. Recovery from inactivation occurred at potentials hyperpolarized to V(rest). Brief periods of hyperpolarization apparently remove K(DR) inactivation and thereby increase the channel pool available to suppress excitability during subsequent depolarization.
authors: Department of Ophthalmology and Visual Sciences, Kellogg Eye Center, University of Michigan, 1000 Wall Street, Ann Arbor, MI 48105, USA.
authors: Michael
authors: M
authors: Weick
authors: Jonathan B
authors: JB
authors: Demb
mesh_terms: D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D000221:Adaptation, Ocular / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D051668:Delayed Rectifier Potassium Channels / Q000037:antagonists & inhibitors / Q000502:physiology*; D004558:Electric Stimulation / Q000379:methods; D006168:Guinea Pigs; D008564:Membrane Potentials / Q000502:physiology; D018408:Patch-Clamp Techniques; D010775:Photic Stimulation / Q000379:methods; D026902:Potassium Channel Blockers / Q000494:pharmacology; D012165:Retinal Ganglion Cells / Q000187:drug effects / Q000502:physiology*; D026941:Sodium Channel Blockers / Q000494:pharmacology; D019789:Tetraethylammonium / Q000494:pharmacology
chemical_list: D002121:Calcium Channel Blockers; D051668:Delayed Rectifier Potassium Channels; D026902:Potassium Channel Blockers; D026941:Sodium Channel Blockers; D019789:Tetraethylammonium