Ca2+ -Activated K+ Current at Presynaptic Terminals of Goldfish Retinal Bipolar Cells

Neurosci Res. 1997 Mar;27(3):219-28. doi: 10.1016/s0168-0102(97)01155-3.

Abstract

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Calcium / pharmacology*
  • Dose-Response Relationship, Drug
  • Goldfish
  • Potassium Channels / drug effects*
  • Presynaptic Terminals / drug effects*
  • Retina / drug effects*

Substances

  • Potassium Channels
  • Calcium