Cyclic AMP formation in Tetrahymena pyriformis is controlled by a K +-conductance

Responses of the cAMP generating system of Tetrahymena to changes in the concentrations of external [K +] or [Ca +] ions were examined. When Tetrahymena are equilibrated in high [K +] buffers, intracellular levels of cAMP decreased to 40% within 2 h. Hyperpolarization of the cells by dilution of external [K +] to one-eighth of its original concentration instantly stimulated intracellular cAMP formation. Manipulations of the K + resting conductance of Tetrahymena by equilibration in buffers of different K + content greatly affected the responsivity of the adenylyl cyclase. Hyperpolarization of the cell by addition of Ca 2+ also resulted in a rapid generation of cAMP. Blockade of K + conductances by the K + channel blockers tetraethylammoniwn, quinine, and Cs +, dose-dependently inhibited hyperpolarization-stimulated cAMP formation. The data indicate that a hyperpolarization-activated K + current is directly coupled to adenylyl cyclase regulation.