Regional expression of L-type calcium channel subunits during cardiac development

The contraction of cardiomyocytes is initiated by the entrance of extracellular calcium through specific calcium channels. Within the myocardium, L-type calcium channels are most abundant. In the heart, the main pore-forming subunit is the alpha1C, although there is a larger heterogeneity on auxiliary beta subunits. We have analyzed the distribution pattern of different alpha1C and beta subunits during cardiac development by immunohistochemistry. We observed homogeneous expression of alpha1C and beta subunits within the early tubular heart, whereas regional differences are observed during the late embryogenesis. beta2 and beta4 show differential expression within the embryonic myocardium. alpha1CD1 displays only a transient enhanced expression in the ventricular conduction system. In adult heart, the expression of the different calcium channel subunits analyzed is homogeneous along the entire myocardium except for alpha1CD1 that is practically undetectable. These findings suggest that beta subunits might play a major role in conferring calcium handling heterogeneity within the developing embryonic myocardium, while alpha1C subunits might contribute just transiently.