Temperature dependence of drug blockade of a calcium-dependent potassium channel in cultured hippocampal neurons.
The temperature dependence of drug blockade of a calcium-dependent potassium channel K(Ca) has been studied in cultured CA1 hippocampal neurons. Channel openings from a 70-pS K+ channel were recorded when inside-out patches were exposed to a bath solution containing 140 mM K+ and 0.2 mM Ca2+. The mean open times of channel events were not significantly altered when the bath temperature was lowered from 24 degrees to 14 degrees C (Q10 = 1.2). Introduction of the drug RP-62719 into the bath solution (at 5 microM) resulted in the mean open time of the K(Ca) channel to be diminished by 85% (at 24 degrees C) with no change in the amplitudes of the unitary currents. Over the same temperature range of 24 degrees to 14 degrees C, in the presence of RP-62719, the mean open times were significantly prolonged (Q10 = 2.2). A simple open channel block scheme was used to determine the temperature dependence of the onward- (blocking) and off- (unblocking) rate constants. Thermodynamic analysis, using transition rate theory, showed that the blocking rate constant was associated with a large increase in entropy. The relatively high temperature dependence for channel blockade is not consistent with a rate-limiting process established by simple diffusion of the agent to a channel blocking site. Channel block may involve conformational changes in the channel protein as a consequence of hydrophobic interactions between drug and channel sites.
McLarnon
J G
JG
Department of Pharmacology & Therapeutics, Faculty of Medicine, University of British Columbia, Vancouver, Canada.
Wang
X P
XP
D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology; D055592:Biophysical Phenomena; D001703:Biophysics; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D002839:Chromans; D004594:Electrophysiology; D006624:Hippocampus / Q000378:metabolism*; D007700:Kinetics; D009474:Neurons / Q000378:metabolism; D010880:Piperidines; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D013696:Temperature; D013816:Thermodynamics
D000889:Anti-Arrhythmia Agents; D002839:Chromans; D010880:Piperidines; D015221:Potassium Channels; C063899:terikalant; D002118:Calcium