β-Adrenergic stimulation increases Cav3.1 activity in cardiac myocytes through protein kinase A

The T-type Ca(2+) channel (TTCC) plays important roles in cellular excitability and Ca(2+) regulation. In the heart, TTCC is found in the sinoatrial nodal (SAN) and conduction cells. Cav3.1 encodes one of the three types of TTCCs. To date, there is no report regarding the regulation of Cav3.1 by β-adrenergic agonists, which is the topic of this study. Ventricular myocytes (VMs) from Cav3.1 double transgenic (TG) mice and SAN cells from wild type, Cav3.1 knockout, or Cav3.2 knockout mice were used to study β-adrenergic regulation of overexpressed or native Cav3.1-mediated T-type Ca(2+) current (I(Ca-T(3.1))). I(Ca-T(3.1)) was not found in control VMs but was robust in all examined TG-VMs. A β-adrenergic agonist (isoproterenol, ISO) and a cyclic AMP analog (dibutyryl-cAMP) significantly increased I(Ca-T(3.1)) as well as I(Ca-L) in TG-VMs at both physiological and room temperatures. The ISO effect on I(Ca-L) and I(Ca-T) in TG myocytes was blocked by H89, a PKA inhibitor. I(Ca-T) was detected in control wildtype SAN cells but not in Cav3.1 knockout SAN cells, indicating the identity of I(Ca-T) in normal SAN cells is mediated by Cav3.1. Real-time PCR confirmed the presence of Cav3.1 mRNA but not mRNAs of Cav3.2 and Cav3.3 in the SAN. I(Ca-T) in SAN cells from wild type or Cav3.2 knockout mice was significantly increased by ISO, suggesting native Cav3.1 channels can be upregulated by the β-adrenergic (β-AR) system. In conclusion, β-adrenergic stimulation increases I(Ca-T(3.1)) in cardiomyocytes(,) which is mediated by the cAMP/PKA pathway. The upregulation of I(Ca-T(3.1)) by the β-adrenergic system could play important roles in cellular functions involving Cav3.1.