Biphasic effect of thyrotropin-releasing hormone on membrane K+ permeability in rat clonal pituitary cells.

The effect of thyrotropin-releasing hormone (TRH) on the membrane electrical properties of the rat clonal pituitary cell (GH3) was studied in Cl- -free solution. TRH induced biphasic changes in the membrane K+ permeability, namely a transient increase followed by a prolonged decrease. The late decrease in K+ permeability is responsible for the enhanced generation of action potentials.