β2-adrenergic receptor signaling acts via NO release to mediate ACh-induced activation of ATP-sensitive K+ current in cat atrial myocytes

In atrial myocytes, an initial exposure to isoproterenol (ISO) acts via cAMP to mediate a subsequent acetylcholine (ACh)-induced activation of ATP-sensitive K+ current (I-KATP). In addition, beta-adrenergic receptor (beta-AR) stimulation activates nitric oxide (NO) release. The present study determined Whether the conditioning effect of beta-AR stimulation acts via beta(1)- and/or beta(2)-ARs and whether it is mediated via NO signaling. 0.1 muM ISO plus ICI 118.551 (ISO-beta(1)-AR stimulation) or ISO plus atenolol (ISO-beta(2)-AR stimulation) both increased L-type Ca2+ current (I-Ca,I-L) markedly, but only ISO-beta(2)-AR stimulation mediated ACh-induced activation of I-KATP. 1 muM zinterol (beta(2)- AR agonist) also increased and mediated ACh-activated I-KATP. Inhibition of NO synthase (10 muM L-NIO), guanylate cyclase (10 muM ODQ), or cAMP-PKA (50 muM Rp-cAMPs) attenuated zinterol-induced stimulation Of I-Ca,I-L and abolished ACh-activated I-KATP, Spermine-NO (100 muM; an NO donor) mimicked beta2-AR stimulation, and its effects were abolished by Rp-cAMPs. Intracellular dialysis of 20 muM protein kinase inhibitory peptide (PKI) abolished zinterol-induced stimulation of Measurements of intracellular NO ([NO](i)) using the fluorescent indicator DAF-2 showed that ISO-beta(2)-AR Stimulation or zinterol increased [NO](i). L-NIO (10 muM) blocked ISO- and zinterol-induced increases in [NO](i). ISO-beta(1)-AR stimulation failed to increase [NO](i). Inhibition of G(i)-protein by, pertussis toxin significantly inhibited zinterol-mediated increases in [NO](i). Wortmannin (0.2 muM) or LY294002 (10 muM), inhibitors of phosphatidylinositol 3'-kinase (PI-3K), abolished the effects of zinterol to both mediate ACh-activated I-KATP and stimulate [NO](i). We conclude that both beta(1)- and beta(2)-ARs stimulate cAMP. beta(2)-ARs act via two signaling pathways to stimulate cAMP, one of which is mediated via G(i)-protein and PI-3K coupled to NO-cGMP signaling. Only beta(2)-ARs acting exclusively via NO signaling mediate ACh-induced activation of I-KATP. NO signaling also contributes to beta(2)-AR stimulation of The differential effects of beta(1)- and beta(2)-ARs can be explained by the coupling of these two beta-ARs to different effector signaling pathways.