In the heart, the main pathway for calcium influx is mediated by L-type calcium channels, a multi-subunit complex composed of the pore-forming subunit CaV1.2 and the auxiliary subunits CaVα2δ1 and CaVβ2. To date, five distinct CaVβ2 transcriptional start site (TSS) variants (CaVβ2a-e) varying only in the composition and length of the N-terminal domain have been described, each of them granting distinct biophysical properties to the L-type current. However, the physiological role of these variants in Ca2+ handling in the native tissue has not been explored. Our results show that four of these variants are present in neonatal rat cardiomyocytes. The contribution of those CaVβ2 TSS variants on endogenous L-type current and Ca2+ handling was explored by adenoviral-mediated overexpression of each CaVβ2 variant in cultured newborn rat cardiomyocytes. As expected, all CaVβ2 TSS variants increased L-type current density and produced distinctive changes on L-type calcium channel (LTCC) current activation and inactivation kinetics. The characteristics of the induced calcium transients were dependent on the TSS variant overexpressed. Moreover, the amplitude of the calcium transients varied depending on the subunit involved, being higher in cardiomyocytes transduced with CaVβ2a and smaller in CaVβ2d. Interestingly, the contribution of Ca2+ influx and Ca2+ release on total calcium transients, as well as the sarcoplasmic calcium content, was found to be TSS-variant-dependent. Remarkably, determination of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) messenger RNA (mRNA) abundance and cell size change indicates that CaVβ2 TSS variants modulate the cardiomyocyte hypertrophic state. In summary, we demonstrate that expression of individual CaVβ2 TSS variants regulates calcium handling in cardiomyocytes and, consequently, has significant repercussion in the development of hypertrophy.
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We are thankful to Rocio K. Finol-Urdaneta, Andrés Stutzin, and Luis Michea for constructive discussion to the manuscript. This work was supported by research grants from Fondo Nacional de Desarrollo Científico y Tecnológico (Fondecyt) 1120240 to DV, and Fondecyt 1121078 and Millennium Institute on Immunology and Immunotherapy P09-016-F to FS.
D.V. and T.H. designed the project. C.M., T.H., L.T-D., D.M., M.E., P.D., D.S., and D.V. performed the experiments. D.V., T.H., and F.S. analyzed the data. D.V. wrote the manuscript.
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Moreno, C., Hermosilla, T., Morales, D. et al. Cavβ2 transcription start site variants modulate calcium handling in newborn rat cardiomyocytes. Pflugers Arch - Eur J Physiol 467, 2473–2484 (2015). https://doi.org/10.1007/s00424-015-1723-3
- Calcium transients
- Auxiliary subunits
- L-type calcium current