Urotensin-II receptor stimulation of cardiac L-type Ca2+ channels requires the {beta}{gamma} subunits of Gi/o-protein and phosphatidylinositol 3-kinase-dependent protein kinase C beta 1 isoform [Cell Biology]

February 12th, 2015 by Zhang, Y., Ying, J., Jiang, D., Chang, Z., Li, H., Zhang, G., Gong, S., Jiang, X., Tao, J.

Recent studies have demonstrated that urotensin-II (U-II) plays important roles in cardiovascular actions including cardiac positive inotropic effects and increasing cardiac output. However, the mechanisms underlying these effects of U-II in cardiomyocytes remain still unknown. We show by electrophysiological studies that U-II dose-dependently potentiates L-type Ca2+ currents (ICa,L) in adult rat ventricular myocytes. This effect was U-II receptor (U-IIR)-dependent and was associated with a depolarizing shift in the voltage-dependence of inactivation. Intracellular application of GDP-β-S and pertussis toxin pretreatment, both abolished the stimulatory effects of U-II. Dialysis of cells with the QEHA peptide, but not scrambled peptide SKEE, blocked the U-II-induced response. The phosphatidylinositol 3-kinase (PI3K) inhibitor wortmannin, as well as the class I PI3K antagonist CH132799, blocked the U-II-induced ICa,L response. Protein kinase C antagonists, calphostin C and chelerythrine chloride, as well as dialysis of cells with BAPTA abolished the U-II-induced responses, whereas PKCα inhibition or PKA blockade had no effect. Exposure of ventricular myocytes to U-II markedly increased membrane PKCβ1 expression, while PKCβ1 inhibition pharmacologically or by shRNA targeting abolished the U-II-induced ICa,L response. Functionally, we observed a significant increase in the amplitude of sarcomere shortening induced by U-II; blockade of U-IIR as well as PKCβ inhibition abolished this effect, while Bay K8644 mimicked U-II response. Taken together, our results indicate that U-II potentiates ICa,L through the βγ subunits of Gi/o-protein and downstream activation of the class I PI3K-dependent PKCβ1 isoform. This occurred via the activation of U-IIR and contributes to the positive inotropic effect on cardiomyocytes.
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