Molecular cloning and functional expression of a skeletal muscle dihydropyridine receptor from Rana catesbeiana

In skeletal muscle the dihydropyridine receptor is the voltage sensor for excitation-contraction coupling and an L-type Ca2+ channel. We cloned a dihydropyridine receptor (named Fg alpha 1S) from frog skeletal muscle, where excitation-contraction coupling has been studied most extensively. Fg alpha 1S contains 5600 base pairs coding for 1688 amino acids. It is highly homologous with, and of the same length as, the C-truncated form predominant in rabbit muscle. The primary sequence has every feature needed to be an L-type Ca2+ channel and a skeletal-type voltage sensor. Currents expressed in tsA201 cells had rapid activation (5-10 ms half-time) and Ca2+ dependent inactivation. Although functional expression of the full Fg alpha 1S was difficult, the chimera consisting of Fg alpha 1S domain I in the rabbit cardiac Ca channel had high expression and a rapidly activating current. The slow native activation is therefore not determined solely by the alpha 1 subunit sequence. Its Ca2+-dependent inactivation strengthens the notion that in rabbit skeletal muscle this capability is inhibited by a C-terminal stretch (Adams, B., and Tanabe, T, (1997) J. Gen. Physiol. 110, 379-389). This molecule constitutes a new tool for studies of excitation-contraction coupling, gating, modulation, and gene expression.