CALCITONIN-GENE-RELATED PEPTIDE ACTIVATED ATP-SENSITIVE K-MUSCLE VIA PROTEIN-KINASE-A( CURRENTS IN RABBIT ARTERIAL SMOOTH)

1. Whole-cell K+ currents activated by calcitonin gene-related peptide (CGRP) in smooth muscle cells enzymatically isolated from rabbit mese nteric arteries were measured in the conventional and perforated confi gurations of the patch clamp technique. The signal transduction pathwa y from CGRP receptors to activation of potassium currents was investig ated. 2. CGRP (10 nM) activated a whole-cell current that was blocked by glibenclamide (10 mu M), an inhibitor of ATP-sensitive K+ channels. Elevating intracellular ATP reduced glibenclamide-sensitive currents. CGRP increased the glibenclamide-sensitive currents by 3- to 6-fold i n cells dialysed with 0.1 mM ATP, 3.0 mM ATP or in intact cells. The r eversal potential of the glibenclamide-sensitive current in the presen ce of CGRP shifted with the potassium equilibrium potential, while its current-voltage relationship exhibited little voltage dependence. 3. Forskolin (10 mu M), an adenylyl cyclase activator, Sp-cAMPS (500 mu M ) and the catalytic subunit of protein kinase A increased glibenclamid e-sensitive K+ currents 2.1-, 3.3- and 8.2-fold, respectively. 4. Nitr ic oxide and nitroprusside did not activate glibenclamide-sensitive K currents. 5. Dialysis of the cell's interior with inhibitors of prote in kinase A (synthetic peptide inhibitor, 4.6 mu M or H-8, 100 mu M) c ompletely blocked activation of K+ currents by CGRP. 6. Our results su ggest the following signal transduction scheme for activation of K+ cu rrents by CGRP in arterial smooth muscle: (1) CGRP stimulates adenylyl cyclase, which leads to an elevation of cAMP; (2) cAMP activates prot ein kinase A, which opens ATP-sensitive K+ channels.