Progressive predominance of 'skeletal' versus 'cardiac' types of excitation-contraction coupling during in vitro skeletal myogenesis.

Simultaneous recordings, in the presence or absence of cadmium, of current and contraction of skeletal muscle cells in primary culture (myoballs) showed that the relative part of contraction depending on calcium current progressively decreases with the age of cells whereas the cadmium-insensitive component becomes predominant. The coexistence of "cardiac" and "skeletal" excitation-contraction coupling mechanisms in developing muscle and its developmental regulation are consistent with recent molecular data showing the expression, in newborn animals, of an abbreviated isoform of the alpha 1 subunit of the DHP-receptor of muscle cells.