The function of calcineurin and ERK1/2 signal in the antihypertrophic effects of κ-opioid receptor stimulation on myocardial hypertrophy induced by isoprenaline

The aim of the present study, performed in an in vitro model of cardiac hypertrophy, was to examine the possible function of calcineurin and ERK1/2 in the inhibitory effects of κ-opioid receptor stimulation on Ca2+ transients and myocardial hypertrophy induced by β1-adrenoceptor stimulation. We determined the effects of trans-(±)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl]-benzeneacetamid methanesulfonate salt (U50,488H), a selective κ-opioid receptor agonist, on the enhancement of spontaneous Ca2+ transients and the induction of hypertrophy by isoprenaline, a β-adrenoceptor agonist, in cultured neonatal ventricular myocytes. Total protein content, [3 H]leucine incorporation and cell size were used as indices of hypertrophy; calcineurin activity and phospho-ERK1/2 level were determined by immunoblotting. Isoprenaline (10 μmol·L−1) increased all the three indices of hypertrophy, Ca2+ transients, calcineurin activity and the level of phospho-ERK1/2. The effects of isoprenaline were abolished by 1 μmol·L−1 U50,488H in the absence but not in the presence of nor-binaltorphimine, a κ-opioid receptor antagonist. The inhibitory effects of U50,488H were reproduced by cyclosporine-A, an inhibitor of calcineurin, U0126, the inhibitor of ERK1/2 and verapamil, a L-type Ca2+ channel antagonist. In addition, suppression of calcineurin activity by cyclosporine-A was associated with modest suppression of ERK1/2 phosphorylation. Meanwhile, suppression of ERK1/2 phosphorylation by U0126 was associated with modest suppression of calcineurin activity. In conclusion, the inhibitory effects of κ-opioid receptor stimulation involved calcineurin and ERK1/2, and the two signaling pathways showed interaction in the mechanism of antihypertrophic effects afforded by κ-opioid receptor stimulation.