Functional expression of the L-type calcium channel in mice skeletal muscle during prenatal myogenesis

The densities of skeletal muscle intramembrane charge movement and macrosco pic L-type Ca2+ current have been shown to increase during prenatal develop ment. In the present work, the electrophysiological characteristics of L-ty pe Ca2+ channels were analyzed over the embryonic period E14 to E19 using t he whole-cell and cell-attached procedures. At the macroscopic level, the w hole-cell L-type Ca2+ conductance increased 100% between E14 and E19. This enhancement was accompanied by a small negative shift of the voltage depend ence and a marked acceleration of the inactivation kinetics. At the single- channel level, the unitary conductance decreased significantly from 13.2 +/ - 0.1 pS (n = 8) at E14 to 10.7 +/- 0.3 pS (n = 7) at E18 and the open prob ability was multiplied by 2. No significant change of the density of functi onal channels was observed during the same period. In contrast to the densi ty of intramembrane charge movement, which, under the same conditions, has been shown to increase between 16 and 19 days, L-type Ca2+ channels propert ies change mostly between 14 and 16 days, Taken together, these results sug gest that the two functions of the dihydropyridine receptor are carried by two different proteins which could be differentially regulated by subunit c omposition and/or degree of phosphorylation.