Sympathetic Stimulation Upregulates the Ca(2+) Channel Subunit, Ca(V)α2δ1, via the β1 and ERK 1/2 Pathway in Neonatal Ventricular Cardiomyocytes

Intracellular Ca(2+) overload secondary to chronic hemodynamic stimuli promotes the recruitment of Ca(2+)-dependent signaling implicated in cardiomyocyte hypertrophy. The present study tested the hypothesis that sympathetic-mediated hypertrophy of neonatal rat ventricular cardiomyocytes (NRVMs) translated to an increase in calcium influx secondary to the upregulation of Ca(V)1.2 channel subunits. Confocal imaging of norepinephrine (NE)-treated NRVMs revealed a hypertrophic response compared to untreated NRVMs. L-type Ca(V)1.2 peak current density was increased 4-fold following a 24-h stimulation with NE. NE-treated NRVMs exhibited a significant upregulation of Ca(V)α2δ1 and Ca(V)β3 protein levels without significant changes of Ca(V)α1C and Ca(V)β2 protein levels. Pre-treatment with the β(1)-blocker metoprolol failed to inhibit hypertrophy or Ca(V)β3 upregulation whereas Ca(V)α2δ1 protein levels were significantly reduced. NE promoted the phosphorylation of ERK 1/2, and the response was attenuated by the β(1)-blocker. U0126 pre-treatment suppressed NE-induced ERK1/2 phosphorylation but failed to attenuate hypertrophy. U0126 inhibition of ERK1/2 phosphorylation prevented NE-mediated upregulation of Ca(V)α2δ1, whereas Ca(V)β3 protein levels remained elevated. Thus, β(1)-adrenergic receptor-mediated recruitment of the ERK1/2 plays a seminal role in the upregulation of Ca(V)α2δ1 in NRVMs independent of the concomitant hypertrophic response. However, the upregulation of Ca(V)β3 protein levels may be directly dependent on the hypertrophic response of NRVMs.