Effects of β-adrenoceptor stimulation on delayed rectifier K plus currents in canine ventricular cardiomyocytes

BACKGROUND AND PURPOSE While the slow delayed rectifier K+ current (I-Ks) is known to be enhanced by the stimulation of beta-adrenoceptors in several mammalian species, phosphorylation-dependent regulation of the rapid delayed rectifier K+ current (I-Kr) is controversial. EXPERIMENTAL APPROACH In the present study, therefore, the effect of isoprenaline (ISO), activators and inhibitors of the protein kinase A (PKA) pathway on I-Kr and I-Ks was studied in canine ventricular myocytes using the whole cell patch clamp technique. KEY RESULTS I-Kr was significantly increased (by 30-50%) following superfusion with ISO, forskolin or intracellular application of PKA activator cAMP analogues (cAMP, 8-Br-cAMP, 6-Bnz-cAMP). Inhibition of PKA by Rp-8-Br-cAMP had no effect on baseline I-Kr. The stimulating effect of ISO on I-Kr was completely inhibited by selective beta(1)-adrenoceptor antagonists (metoprolol and CGP-20712A), by the PKA inhibitor Rp-8-Br-cAMP and by the PKA activator cAMP analogues, but not by the EPAC activator 8-pCPT-2'-O-Me-cAMP. In comparison, I-Ks was increased threefold by the activation of PKA (by ISO or 8-Br-cAMP), and strongly reduced by the PKA inhibitor Rp-8-Br-cAMP. The ISO-induced enhancement of I-Ks was decreased by Rp-8-Br-cAMP and completely inhibited by 8-Br-cAMP. CONCLUSIONS AND IMPLICATIONS The results indicate that the stimulation of beta(1)-adrenoceptors increases I-Kr, similar to I-Ks,I- via the activation of PKA in canine ventricular cells.