Kinetics of the Ca(2+)-activated K+ channel in rat hippocampal neurons.
The kinetics of the large-conductance Ca(2+)-activated K+ channel (235 pS in symmetrical 150 mM K+) were examined in the inside-out mode of the patch clamp technique. The open probability of the channel increased when [Ca2+]i, [Sr2+]i, or [Ba2+]i was increased. The [Ca2+]i-response relation was fitted with a Hill coefficient of 2 and half-maximum concentrations of 185, 80, 14.5, and 5.5 microM at -40, -20, +20, and +40 mV, respectively. The channel was blocked by TEA or Ba2+. The open-time histogram showed a single exponential component and the closed-time histogram showed at least two exponential components at various [Ca2+]i. Increasing [Ca2+]i decreased the time constant of the slow component of the closed-time histogram. Cell-attached patch recording revealed activation of the large-conductance Ca(2+)-activated K+ channel (BK channel) during the action potential. The deactivation time course was consistent with the fast after-hyperpolarization. A minimum model of the channel, close(2)-close(1)-open, where the transition from close(2) to close(1) requires the binding of 2 Ca2+, reconstructed quick activation of the channel if [Ca2+]i of 40 microM was assumed.
Yoshida
A
A
Second Department of Oral Surgery, Faculty of Dentistry, Kyushu University, Fukuoka, Japan.
Oda
M
M
Ikemoto
Y
Y
D000200:Action Potentials; D000818:Animals; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D004553:Electric Conductivity; D005260:Female; D006624:Hippocampus / Q000378:metabolism*; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000187:drug effects; D007700:Kinetics; D008297:Male; D008564:Membrane Potentials; D009474:Neurons / Q000378:metabolism; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D001464:Barium; D019789:Tetraethylammonium; D002118:Calcium