Activation of inwardly rectifying Kir2.x potassium channels by β3-adrenoceptors is mediated via different signaling pathways with a predominant role of PKC for Kir2.1 and of PKA for Kir2.2

Abstract

beta(3)-adrenoceptors have recently been shown to induce a complex modulation of intracellular signaling pathways including cyclic guanine monophosphate, cyclic adenosine monophosphate, nitric oxide, and protein kinases A and C. They are expressed in a broad variety of tissues including the myocardium, vascular smooth muscle, and endothelium. In those tissues, resting membrane potential is controlled mainly by inwardly rectifying potassium channels of the Kir2 family namely, Kir2.1 in the vascular smooth muscle, Kir2.1-2.3 in the myocardium, and Kir2.1-2.2 in the endothelium. In the present study, we investigated the possible modulation of Kir2 channel function by beta(3)-adrenoceptors in an expression system. Human-cloned beta(3)-adrenoceptors and Kir2.1 (KCNJ2), Kir2.2 (KCNJ12), and Kir2.3 (KCNJ4) channels were coexpressed in Xenopus oocytes, and currents were measured with double-microelectrode voltage clamp. Activation of beta(3)-adrenoceptors with isoproterenol resulted in markedly increased currents in Kir2.1 and in Kir2.2 potassium channels with EC50 values of 27 and 18 nM, respectively. In contrast, Kir2.3 currents were not modulated. Coapplication of specific inhibitors of protein kinase A (KT-5720) and calmodulin kinase II (KN-93) had no effects on the observed regulation in Kir2.1. However, coapplication of protein kinase C (PKC) inhibitors staurosporine and chelerythrine suppressed the observed effect. In Kir2.2, coapplication of KT-5720 reduced the effect of beta(3)-adrenoceptor activation. No differences in current increase after application of isoproterenol were observed between mutant Kir2.2 potassium channels lacking all functional PKC phosphorylation sites and Kir2.2 wild-type channels. In heteromeric Kir2.x channels, all types of heteromers were activated. The effect was most pronounced in Kir2.1/Kir2.2 and in Kir2.2/Kir2.3 channels. In summary, homomeric and heteromeric Kir2.x channels are activated by beta(3)-adrenoceptors via different protein kinase-dependent pathways: Kir2.1 subunits are modulated by PKC, whereas Kir2.2 is modulated by protein kinase A. In heteromeric composition, a marked activation of currents can be observed particularly with involvement of Kir2.2 subunits. This regulation may contribute to the hyperpolarizing effects of beta(3)-adrenoceptors in tissues that exhibit modulation by Kir2 channel function.

Beta-adrenergic stimulation reverses the I Kr–I Ks dominant pattern during cardiac action potential

“…Previous studies of the β-adrenergic stimulation effects on I K1 have reported controversial results. Facilitation of I K1 by isoproterenol treatment was reported by Trombe et al [26], Gadsby et al [7] and Scherer et al [24], whereas reduction of I K1 by isoproterenol was reported by Koumi et al [14], Wischmeyer et al [29], and Fauconnier et al [6]. The above experiments were all conducted using traditional V-clamp technique.…”

Expression of a poriferan potassium channel: insights into the evolution of ion channels in metazoans

“…3B) shows 5-fold growth of the inward current without a significant change in the reversal potential and without an increase in the outward current over nearly 2 h. Similar results were obtained from all cells injected with AmqKirB although the rate of increase of inward current varied from cell-to-cell. Run-up has been reported for vertebrate Kir2.1 and Kir2.2 currents and may be explained by PKA activity whereas these currents were downregulated by activation of PKC (Fakler et al, 1994;Scherer et al, 2007;Zitron et al, 2004). ] o , caused the reversal potentials for AmqKir currents to shift in accordance with the E K .…”

Smooth Muscle Ion Channels and Regulation of Vascular Tone in Resistance Arteries and Arterioles

“…Currents through K IR 2.2 channels are increased by activated PKA through phosphorylation of S430 (1653). Additional studies have shown that activation of β 3 -adrenoreceptors increases currents through K IR 2.1 and K IR 2.2 channels (1259). For K IR 2.1, this appears to involve PKC, for K IR 2.2, cAMP and PKA-mediated activation (1259).…”