Effects of Corticotrophin Releasing Factor, Muscarine and Somatostatin on Rubidium and Potassium Efflux from Mouse AtT-20 Pituitary Cells.
Effects of secretagogues and anti-secretagogues of ACTH secretion on K+ permeability in the clonal pituitary cell line AtT-20 were measured by recording 86Rb or 42K efflux. Efflux was accelerated by the secretagogues K+, corticotrophin, forskolin, isoprenaline, and the Ca-ionophore A23187. Efflux was reduced by the inhibitors somatostatin, muscarine, and oxotremorine, or by removing external Ca. Efflux was also reduced by the K+-channel blocking compound d-tubocurarine but not by tetraethylammonium. Muscarine, oxotremorine, somatostatin, and 0 Ca2+ also reduced intracellular Ca2+ measured by quin-2 fluorescence. It is suggested that most of the resting 86Rb or 42K efflux measured under these conditions occurs via tubocurarine-sensitive Ca2+-dependent K+-channels, and that changes in efflux rate produced by secretagogues or anti-secretagogues are secondary to changes in intracellular Ca2+.
Luini
A.
A
Istituto di Richerche Farmacologiche 'Mario Negri', Consorzio Mario Negri Sud, S. M. Imbaro (CH) 66030, Italy.
Brown
D. A.
DA