Ca2+ -activated K+ current at presynaptic terminals of goldfish retinal bipolar cells.
Properties of the Ca2+ -activated K+ current (I[K(Ca)]) were investigated in bipolar cells isolated from the goldfish retina. Pharmacological experiments and single channel current recordings demonstrated that I[K(Ca)] represented currents through BK channels, which were confined mostly to the presynaptic terminal. The ensemble noise analysis of I[K(Ca)], which was evoked following the activation of presynaptic Ca2+ current, revealed that the single channel conductance and open probability (P(o)) were approximately 50 pS ([K+]o = 2.6 mM, [K+]i = 140 mM) and 0.6 at 0 mV, respectively. To estimate [Ca2+]i at the cytosolic side of BK channels, activation of I[K(Ca)] was examined in Ca2+-loaded bipolar cells bathed in Co2+ solution. [Ca2+]i was monitored using furaptra fluorimetry. It was found that [Ca2+]i ranged between 10 and 20 microM when P(o) was 0.6. A high concentration of BAPTA ( > 20 mM) was required to suppress I[K(Ca)]. Under this condition, channel number was reduced without changing P(o). Therefore, it is likely that some BK channels are co-localized with Ca2+ channels in presynaptic terminals of retinal bipolar cells.
Sakaba
T
T
Department of Psychology, Graduate School of Humanities and Sociology, The University of Tokyo, Bunkyo-ku, Japan.
Ishikane
H
H
Tachibana
M
M
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D006054:Goldfish; D015221:Potassium Channels / Q000187:drug effects*; D017729:Presynaptic Terminals / Q000187:drug effects*; D012160:Retina / Q000187:drug effects*
D015221:Potassium Channels; D002118:Calcium