Kir2.x inward rectifier potassium channels are differentially regulated by adrenergic α1A receptors

Inhibition of IK1 currents by adrenergic α1 receptors has been observed in cardiomyocytes and has been linked to arrhythmogenesis in an animal model. Both PKC-dependent and PKC-independent pathways have been implied in this regulation. The underlying molecular mechanisms, however, have not been elucidated to date. The molecular basis of native IK1 current is mainly formed by Kir2.1 (KCNJ2), Kir2.2 (KCNJ12) and Kir2.3 (KCNJ4) channels that are differentially regulated by protein kinases. We therefore sought to investigate the role of those different Kir2.x channel subunits in this regulation and to identify the major signalling pathways involved.Adrenergic α1A receptors (the predominant cardiac isoform) were co-expressed with cloned Kir2.1, Kir2.2 and Kir2.3 channels in Xenopus oocytes and electrophysiological experiments were performed using two-microelectrode voltage clamp. Native IK1 currents were measured with the whole-cell patch clamp technique in isolated rat ventricular cardiomyocytes.Activation of co-expressed adrenergic α1A receptors by phenylephrine induced differential effects in Kir2.x channels. No effect was noticed in Kir2.1 channels. However, a marked inhibitory effect was observed in Kir2.2 channels. This regulation was not attenuated by inhibitors of PKC, CamKII and PKA (chelerythrine, KN-93, KT-5720), and mutated Kir2.2 channels lacking functional phosphorylation sites for PKC and PKA exhibited the same effect as Kir2.2 wild-type channels. By contrast, the regulation could be suppressed by the general tyrosine kinase inhibitor genistein and by the src tyrosine kinase inhibitor PP2 indicating an essential role of src kinases. This finding was validated in rat ventricular cardiomyocytes where co-application of PP2 strongly attenuated the inhibitory regulation of IK1 current by adrenergic α1 receptors. The inactive analogue PP3 was tested as negative control for PP2 and did not reproduce the effects of PP2. In Kir2.3 channels, a marked inhibitory effect of α1A receptor activation was observed. This regulation could be attenuated by inhibition of PKC with chelerythrine or with Ro-32-0432, but not by tyrosine kinase inhibition with genistein.In summary, on the molecular level the inhibitory regulation of IK1 currents by adrenergic α1A receptors is probably based on effects on Kir2.2 and Kir2.3 channels. Kir2.2 is regulated via src tyrosine kinase pathways independent of protein kinase C, whereas Kir2.3 is inhibited by protein kinase C-dependent pathways. Src tyrosine kinase pathways are essential for the inhibition of native IK1 current by adrenergic α1 receptors. This regulation may contribute to arrhythmogenesis under adrenergic stimulation.