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Am J Physiol Endocrinol Metab 266: E318-E325, 1994;
0193-1849/94 $5.00
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AJP - Endocrinology and Metabolism, Vol 266, Issue 3 E318-E325, Copyright © 1994 by American Physiological Society

ARTICLES

Activation of G protein-coupled K+ channels by dopamine in human GH-producing cells

K. Takano, S. Asano and N. Yamashita
Fourth Department of Internal Medicine, University of Tokyo School of Medicine, Japan.

Dopamine (DA) inhibited the secretion of growth hormone (GH) from cultured human GH-secreting adenoma cells. The mechanism of this DA effect on these cultured cells was investigated with electrophysiological techniques. Under current clamp, DA (10(-6) M) hyperpolarized the membrane and arrested Ca(2+)-dependent action potentials. Voltage clamp experiments revealed that this membrane hyperpolarization was the result of a K+ conductance increase caused by DA. The current-voltage relationship of the DA-induced K+ current showed an inward-going rectification. Application of sulpiride (10(-6) M) abolished the DA-induced K+ current, indicating that the hyperpolarization was caused by the activation of D2-like receptors. Pertussis toxin (PTX) treatment eliminated the DA-induced K+ current as well as the DA-induced inhibition of GH secretion. An intracellular application of guanosine-5'-O-(3-thiotriphosphate) (100 microM) evoked a spontaneous increase in the K+ current in the absence of an agonist, and the application of DA did not further increase conductance. Intracellular application of guanosine-5'-O-(2-thiodiphosphate) (2 mM) inhibited the DA-induced K+ current. These results indicate that the DA-induced K+ channel is coupled to a G protein. When adenosine 3',5'-cyclic monophosphate (cAMP, 100 microM) was added to the patch-pipette solution, the DA-induced K+ current was still observed, indicating that the DA-induced K+ current was not caused by an inhibition of cAMP production.(ABSTRACT TRUNCATED AT 250 WORDS)


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