Secretagogue-induced exocytosis recruits G protein-gated K+ channels to plasma membrane in endocrine cells

Stimulation-regulated fusion of vesicles to the plasma membrane is an essen tial step for hormone secretion but may also serve for the recruitment of f unctional proteins to the plasma membrane. While studying the distribution of G protein-gated K+ (K-G) channels in the anterior pituitary lobe, we fou nd K-G channel subunits Kir3.1 and Kir3.4 localized on the membranes of int racellular dense core vesicles that contained thyrotropin. Stimulation of t hese thyrotroph cells with thyrotropin-releasing hormone provoked fusion of vesicles to the plasma membrane, increased expression of Kir3.1 and Kir3.4 subunits in the plasma membrane, and markedly enhanced K-G currents stimul ated by dopamine and somatostatin, These data indicate a novel mechanism fo r the rapid insertion of functional ion channels into the plasma membrane, which could form a new type of negative feedback control loop for hormone s ecretion in the endocrine system.