ABSTRACT
The DHP receptor (DHPR) of skeletal muscle is a heteropentameric complex consisting of α1(175 and 212 kDa), α2(143 kDa), δ(27 kDa), β(56 kDa) and γ(30 kDa) subunits (Fig. 8.1; Catterall, 1991a, b, 1992a, b, 1995; G.Varadi et al., 1995; Gurnett and Campbell, 1996). Two forms of the α 1 subunit have been identified (De Jongh et al., 1989, 1991) with molecular weights of 212kDa and 175kDa, respectively. The truncated 175kDa form accounts for ≈90% of the α 1 subunits in purified T-tubules. The structure of the α 1 subunit deduced from cDNA sequence (Tanabe et al, 1987, 1988, 1990a, b, 1991, 1993; De Jongh et al., 1989) bears startling similarity to the predicted structures of the voltage-sensitive Na+ channels
Fig. 8.1. The subunit composition of the dihydropyridine receptor complex (DHPR) of T-tubules and plasma membranes. The α 1 subunit serves both as voltage sensor and Ca2+ channel in excitation-contraction coupling, and contains the binding site for the Ca2+ channel blocker dihydropyridine. The α 1 subunit interacts with the α 2 -δ and γsubunits, that are heavily glycosylated on their
extra cellular surface (ψ). The α 1 and β subunits have sites for c-AMPdependent phosphorylation (P) on the cytoplasmic surface, that modulate their activity. (From Catterall (1995). Cell 64:871-874.
