PROTEIN-KINASE A MEDIATES ACTIVATION OF ATP-SENSITIVE K+ CURRENTS BY CGRP IN GALLBLADDER SMOOTH-MUSCLE

The signal transduction mechanisms underlying the activation of ATP-sensitive potassium (K-ATP) current by calcitonin gene-related peptide (CGRP) in gallbladder smooth muscle were examined with intracellular microelectrode recording and whole cell patch-clamp techniques. In the intact gallbladder preparation, the adenylyl cyclase activator forskolin hyperpolarized the membrane potential and abolished spontaneous action potentials. This response was inhibited by the K-ATP channel blocker glibenclamide. CGRP (10 nM), forskolin (10 mu M), the membrane-permeable adenosine 3',5'-cyclic monophosphate (cAMP) analogue adenosine 3',5'cyclic monophosphothioate (Sp-cAMP[S]; 500 mu M), and the catalytic subunit of protein kinase A (100 U/ml) activated glibenclamide-sensitive currents in enzymatically dissociated gallbladder smooth muscle cells. CGRP activation of potassium currents was prevented by dialysis of the cell cytoplasm with guanosine 5'-O-(2-thiodiphosphate) (5 mM) or a specific peptide inhibitor of protein kinase A (2.3 mu M). Okadaic acid (5 mu M), a phosphatase inhibitor, slowed the deactivation of the K-ATP current, following removal of CGRP. The results of this study indicate that CGRP hyperpolarizes gallbladder smooth muscle by elevation of cAMP and subsequent stimulation of protein kinase A.