Potassium channels in pituitary cells in the teleost, Gillichthys mirabilis

We have examined whole-cell K⁺ currents and a Ca²⁺-dependent K⁺ channel at the single channel level in rostral pars distalis cells of Gillichthys mirabilis. Whole-cell K⁺ currents activated by depolarizing pulses have an inactivating component and a sustained component. The magnitude of both of these components is increased when a hyperpolarizing prepulse is delivered prior to depolarization. Both components are partially blocked by application of 5 mM TEA⁺. The Ca-dependent K⁺ channel, (K(Ca)), was sensitive to 2 mM TEA⁺ in outside-out patches (O/O) but not in inside-out patches (I/O). Channel open probability (P(o)) was dependent on membrane potential (Vm), with depolarization leading to an increase in P(o). Calcium on the cytoplasmic face of I/O patches increased channel P(o) in a dose-dependent manner. A portion of the single K(Ca) channels studied displayed inactivation after depolarizing pulses. These channels may be a component of the inactivating whole-cell current.