Modulation of L-type Ca²⁺ channel current density and inactivation by β-adrenergic stimulation during murine cardiac embryogenesis

Background: L-type Ca2+ current (ICaL) is a key regulatory and functional element during early embryonic cardiomyogenesis. As the embryonic heart underlies hormonal modulation, e.g. catecholamines, we aimed at studying effects of β-adrenergic stimulation on ICaL densities and inactivation kinetics during murine heart development. Methods: ICaL was recorded applying the whole-cell patch-clamp technique in ventricular myocytes of early embryonic (EDS, E9.5-11.5) and late developmental, fetal (LDS, E16.5-18.5) stages as well as adult cardiomyocytes. To distinguish between Ca2+ -(CDI) and voltage-dependent inactivation (VDI), Ca2+ was replaced with Ba2+ in the extracellular recording solution. The β-adrenergic signaling pathway was simulated by applying isoproterenol (Iso). Results: Basal current densities showed an increase of ICaL during development (EDS: -9.61 ± 1.97 pA/pF, n = 9; LDS: -13.2 ± 4.26 pA/pF, n = 12; adult: -16.1 ± 4.63 pA/pF, n = 5). Iso (1 μM) enhanced ICaL density with low effects at EDS (17.1 ± 3.58%, n = 8, P > 0.05) but strong effects at LDS (74.1 ± 3.77%, n = 8, P < 0.01) and in adults (90.6 ± 7.01%, n = 6, P < 0.001). The current availability was significantly higher at LDS as compared to EDS and elevated after application of Iso. In the presence of Ca2+, the fast phase of ICaL inactivation (τf) was significantly enhanced by Iso at LDS. The slow phase of inactivation (τs) was unaltered at both developmental stages. However, VDI was significantly reduced under Iso in LDS and adult cardiomyocytes. Conclusion: These results imply that β-adrenergic modulation becomes of importance especially during fetal heart development. CDI and VDI of ICaL are modulated by β-adrenergic stimulation in fetal but not in early embryonic mouse cardiomyocytes. Furthermore our data suggest important changes of the L-type Ca2+ channel protein, and/or maturation of the Ca2+-induced Ca2+ release (CICR) machinery. © Steinkopff Verlag Darmstadt 2008.