Inactivation of a high conductance calcium dependent potassium current in rat hippocampal neurons.
Inactivating, high conductance BK-type currents have been recorded from inside-out patches (internal and external K+ of 140 mM and 5 mM, respectively), obtained from cultured rat hippocampal neurons. The presence of prominent inactivation, not normally associated with BK channel activity, was dependent on two factors: a depolarizing step to 0 mV from a holding level of -80 mV and internal calcium at a concentration of 0.7 microM. Without the prior conditioning step to a negative potential, unitary currents were not evident at 0 mV; in addition, such currents were not elicited with the stimulus protocol if the internal Ca2+ was reduced to a level of 0.3 microM. Concomitant with current inactivation was the finding of a delayed activation of BK currents following the depolarizing step. Higher internal calcium, at 100 microM, led to persistent and sustained channel activity at 0 mV which was not dependent on a prior step to -80 mV. These results may be relevant to the complex nature of the repolarizing neuronal current Ic which is the macroscopic analogue of the unitary BK current.
McLarnon
J G
JG
Department of Pharmacology and Therapeutics, Faculty of Medicine, University of British Columbia, Vancouver, Canada.
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002478:Cells, Cultured / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D006624:Hippocampus / Q000187:drug effects*; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains
D015221:Potassium Channels; D002118:Calcium