The significance of Gprotein-gated inwardly rectifying K^+ channel in the anterior pituitary endcrine cells

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G protein-gated inwardly rectifying K+ (K_G) channel, a member of inwardly rectifying K^+ channel, is directly activated by pertussis toxin-sensitive G proteins.In endocrine organs, i.e., the anterior pituitary lobe, it was reported that some neurotransmitters including dopamine and somatostatin hyperpolarize the membrane by activating K_G channels, which results in the inhibition of hormone secretion.We found GIRK1 (Kir3.1), the main subunit of K_G channels, to be localized predominantly on the membranes of intracellular dense core vesicles which contained thyrotropin.Stimulation of these thyrotroph cells with thyrotrpin-releasing-hormone provoked fusion of vesicles to the plasma membrane, increased expression of GIRK1 subunit in the plasma membrane, and markedly enhanced K_G currents stimulated by dopamine and somatostatin.These data indicate a novel mechanism for the rapid insertion of functional ion channels into the plasma membrane, which could form a new type of negative feedback control loop for hormone secretion in the endocrine system.