Intracellular Ca2+ overload secondary to chronic hemodynamic stimuli promotes the recruitment of Ca2+-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 CaV1.2 channel subunits. Confocal imaging of norepinephrine (NE)-treated NRVMs revealed a hypertrophic response compared to untreated NRVMs. L-type CaV1.2 peak current density was increased 4-fold following a 24-h stimulation with NE. NE-treated NRVMs exhibited a significant upregulation of CaVα2δ1 and CaVβ3 protein levels without significant changes of CaVα1C and CaVβ2 protein levels. Pre-treatment with the β1-blocker metoprolol failed to inhibit hypertrophy or CaVβ3 upregulation whereas CaVα2δ1 protein levels were significantly reduced. NE promoted the phosphorylation of ERK 1/2, and the response was attenuated by the β1-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 CaVα2δ1, whereas CaVβ3 protein levels remained elevated. Thus, β1-adrenergic receptor-mediated recruitment of the ERK1/2 plays a seminal role in the upregulation of CaVα2δ1 in NRVMs independent of the concomitant hypertrophic response. However, the upregulation of CaVβ3 protein levels may be directly dependent on the hypertrophic response of NRVMs.

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case for the Cav2.1 channel, a critical component of the neurotransmitter exocytosis machinery. In these channels, CaM has a well-described role in mediating the opposing phenomena of calcium-dependent facilitation (CDF) and calcium-dependent inactivation (CDI). CDF increases the calcium entry through Cav2.1 and is controlled by the C-lobe of CaM, while the N-lobe of CaM mediates the decrease of calcium entry characteristic of CDI. Mutations in CaM are known to cause severe clinical phenotypes known as calmodulinopathies, in which patients may exhibit long-QT syndrome (LQTS), catecholaminergic polymorphic ventricle tachycardia (CPVT), or sudden cardiac death. Moreover, LQTS in calmodulinopathies are sometimes comorbid with neurological symptoms including developmental delay, seizures, and autism. While the LQTS phenotype is well explained by a loss of CDI in cardiac Ca V 1.2 channels, little is known about the effects of these mutations on the neuronal Ca V 2.1 channel. Given the importance of CaM mediated regulation of Ca V 2.1, we probed the effect of CaM mutations on the regulation of these channels. Indeed, clinically relevant CaM mutants produced a decrease in CDF in vitro, highlighting the ability for a single mutation in CaM to exert profoundly different effects on different channel subtypes. Moreover, as the number of known calmodulinopathy mutations continues to grow, so does the potential for significant neurological effects, emphasizing the importance of these mutations beyond cardiac channels.