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Cyclic AMP formation in Tetrahymena pyriformis is controlled by a K(+)-conductance
1Universität Tübingen, Fakultät für Chemie und Pharmazie, Germany.
Abstract:
Responses of the cAMP generating system of Tetrahymena to changes in the concentrations of external [K+] or [Ca2+] 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 Ca2+ also resulted in a rapid generation of cAMP. Blockade of K+ conductances by the K+ channel blockers tetraethylammonium, 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.
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