Expression of the sodium/calcium exchanger in mammalian skeletal muscle cells in primary culture

Previous investigations have demonstrated molecular and functional expressi on, at early phases of development of skeletal muscle cells in primary cult ure, of cardiac isoforms of proteins involved in calcium transport and regu lation, like the L-type calcium channel. Here the expression of the cardiac isoform of the Na+/ Ca2+ exchanger (NCX1) was studied in skeletal muscle c ells developing in vitro, by using biochemical, immunological, and electrop hysiological techniques. Northern and Western blot experiments revealed the presence of this cardiac exchanger and its increasing expression during th e early phases of development. Confocal imaging of myotubes showed an NCX1 distribution that was predominantly sarcolemmal. The whole-cell patch-clamp technique allowed us to record ionic currents, the direction and the ampli tude of which depended on extracellular sodium and calcium concentrations. The developmental changes of this functional expression could be correlated with the molecular NCX1 expression changes. Taken together these data demo nstrate the presence of the NCX1 isoform of the Na+/Ca2+ exchanger during i n vitro myogenesis and reinforce the theory that significant levels of card iac-type proteins are transiently expressed during the early phases of the skeletal muscle cell development. (C) 2000 Academic Press.