Dopamine modulates voltage‐activated potassium currents in zebrafish retinal on bipolar cells

We report a study of the characterization of voltage‐activated potassium (K + ) currents in retinal ON bipolar cells in zebrafish. At single‐channels levels, the open probability of the K + channels increased when the membrane potential was increased. The maximal open proportion was 0.76 ± 0.05 under our testing conditions. In whole‐cell recordings, the K + current displayed two exponential components with the activation time constants of 11–22 msec (tau1) and 0.8–4 msec (tau2). Dopamine modulated the K + current. Dopamine reduced the time constant tau2 when the membrane potential was depolarized to high voltages. A decrease in K + current was seen when dopamine D 1 receptors were selectively activated by SKF38393 or when the D 1 receptor‐coupled G‐proteins were activated by GTP‐γ‐S. The activation of adenylate cyclase by forskolin or the increase of intracellular cAMP concentrations by 8‐Br‐cAMP or Sp‐cAMPS also resulted in a decrease in K + current. Together, the data suggest that dopamine modulates the K + current via D 1 receptor‐coupled G‐protein pathways. © 2005 Wiley‐Liss, Inc.