title: Calcium activates two types of potassium channels in rat hippocampal neurons in culture.
abstract: Several calcium-dependent potassium currents can contribute to the electrophysiological properties of neurons. In hippocampal pyramidal cells, 2 afterhyperpolarizations (AHPs) are mediated by different calcium-activated potassium currents. First, a rapidly activated current contributes to action-potential repolarization and the fast AHP following individual action potentials. In addition, a slowly developing current underlies the slow AHP, which occurs after a burst of action potentials and contributes substantially to the spike-frequency accommodation observed in these cells during a prolonged depolarizing current pulse. In order to investigate the single Ca2(+)-dependent channels that might underlie these currents, we performed patch-clamp experiments on hippocampal neurons in primary culture. When excised inside-out patches were exposed to 1 microM Ca2+, 2 types of channel activity were observed. In symmetrical bathing solutions containing 140 mM K+, the channels had conductances of 19 pS and 220 pS, and both were permeable mainly to potassium ions. The properties of these 2 channels differed in a number of ways. At negative membrane potentials, the small-conductance channels were more sensitive to Ca2+ than the large channels. At positive potentials, the small-conductance channels displayed a flickery block by Mg2+ ions on the cytoplasmic face of the membrane. Low concentrations of tetraethylammonium (TEA) on the extracellular face of the membrane specifically caused an apparent reduction of the large-channel conductance. The properties of the large- and small-conductance channels are in accord with those of the fast and slow AHP, respectively.
authors.affiliation: Department of Pharmacology, University of California, San Francisco 94143.
authors.forename: B
authors.initials: B
authors.lastname: Lancaster
authors.forename: R A
authors.initials: RA
authors.lastname: Nicoll
authors.forename: D J
authors.initials: DJ
authors.lastname: Perkel
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002478:Cells, Cultured; D004553:Electric Conductivity; D004594:Electrophysiology / Q000379:methods; D006624:Hippocampus / Q000502:physiology*; D015640:Ion Channel Gating / Q000187:drug effects; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
chemical_list: D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D019789:Tetraethylammonium; D002118:Calcium