ATP-SENSITIVE K-GENE-RELATED PEPTIDE AND PROTEIN-KINASE-A IN PIG CORONARY ARTERIAL SMOOTH-MUSCLE( CHANNEL ACTIVATION BY CALCITONIN)

1. We used patch clamp to study whole-cell K+ currents activated by ca lcitonin gene-related peptide (CGRP) in smooth muscle cells freshly di ssociated from pig coronary arteries. 2. CGRP (50 nM) activated an inw ard current at -60 mV in symmetrical 140 mM K+ that was blocked by gli benclamide (10 mu M), an inhibitor of ATP-sensitive potassium (K-ATP) channels. CGRP-induced currents were larger in cells dialysed with 0.1 mM ATP than with 3.0 mM ATP. 3. Forskolin (10 mu M) activated a glibe nclamide-sensitive current, as did intracellular dialysis with cAMP (1 00 mu M). The catalytic subunit of cAMP-dependent protein kinase (prot ein kinase A, PKA), added to the pipette solution, activated equivalen t currents in five out of twelve cells. 4. CGRP-induced currents were reduced by the PKA inhibitors adenosine 3',5'-cyclic monophosphorothio ate, R-p-isomer, triethylammonium salt (Rp-cAMPS; 100 mu M) and mocinn amyl)amino)ethyl]-5-isoquinolinesulphonamide dihydrochloride (H-89; 1 mu M), and abolished by inclusion of a PKA inhibitor peptide in the pi pette solution. 5. The beta-adrenergic agonist isoprenaline (10 mu M) also activated a glibenclamide-sensitive K+ current. 6. CGRP-induced c urrents were unaffected by the inhibitor of cGMP-dependent protein kin ase (PKG) KT5823 (1 mu M). Sodium nitroprusside (10 mu M) did not acti vate a glibenclamide-sensitive current in cells held at -60 mV, but di d activate an outward current at +60 mV that was abolished by KT5823, or by 100 nM iberiotoxin (an inhibitor of BKCa channels). 7. Our findi ngs suggest that CGRP activates coronary K-ATP channels through a path way that involves adendylyl cyclase and PKA, but not PKG.