TISSUE-SPECIFIC REGULATION OF G-PROTEIN-COUPLED INWARDLY RECTIFYING K+ CHANNEL EXPRESSION BY MUSCARINIC RECEPTOR ACTIVATION IN OVO

We investigated the effects of muscarinic acetylcholine receptor stimu lation on the expression levels of the G-protein-coupled inwardly rect ifying K+ channel (GIRK) subunits using solution hybridization and imm unoblot analyses, We report here that treatment of chick embryos in ov o with muscarinic agonist causes decreases in mRNA levels encoding GIR K1 and GIRK4 in atria but does not alter GIRK1 expression in ventricle s, In addition, GIRKI protein levels also demonstrate a decrease in at ria upon muscarinic acetylcholine receptor stimulation, Numerous recep tors couple to the activation of the GIRK family of inwardly rectifyin g K+ channels; thus, these decreases represent a novel mechanism for r egulating physiological responses to chronic agonist exposure.