POTASSIUM CHANNELS IN PITUITARY-CELLS IN THE TELEOST, GILLICHTHYS MIRABILIS

We have examined whole-cell K+ currents and a Ca2+-dependent K+ channe l at the single channel level in rostral pars distalis cells of Gillic hthys mirabilis. Whole-cell K+ currents activated by depolarizing puls es have an inactivating component and a sustained component. The magni tude of both of these components is increased when a hyperpolarizing p repulse is delivered prior to depolarization. Both components are part ially blocked by application of 5 mM TEA(+). The Ca-dependent K+ chann el, (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 s ingle K(Ca) channels studied displayed inactivation after depolarizing pulses. These channels may be a component of the inactivating whole c ell current.