Increase in junctional conductance caused by isoproterenol in heart cell pairs is suppressed by cAMP-dependent protein-kinase inhibitor.

The influence of isoproterenol (10(-6) M) on junctional conductance of cell pairs isolated from adult rat ventricle was investigated using two separated voltage-clamp circuits. The drug increased the junctional conductance by 40% (S.E. +/- 11%) (n = 10) within 20 sec. In experiments in which an inhibitor of cAMP dependent-protein Kinase was introduced into the cells the effect of isoproterenol on junctional conductance was totally suppressed. These results support the view that cAMP involved in the fast-modulation of junctional conductance in heart and that the activation of a protein Kinase is needed for the effect of the nucleotide on junctional conductance.