Normalization of current kinetics by interaction between the α₁and β subunits of the skeletal muscle dihydropyridine-sensitive Ca²⁺ channel

Abstract

PURIFICATION of skeletal muscle dihydropyridine binding sites has enabled protein complexes to be isolated from which Ca²⁺ currents have been reconstituted. Complementary DNAs encoding the five subunits of the dihydropyridine receptor, α₁, β, γ, α₂ and δ (ref. 1), have been cloned^2–6 and it is now recognized that α₂ and δ are derived from a common precursor^7,8. The α₁, subunit can itself produce Ca²⁺ currents, as was demonstrated using mouse L cells lacking α₂δ (refs 9,10), β (ref. 10) and γ (our unpublished results). In L cells, stable expression of skeletal muscle α₁ alone was sufficient to generate voltage-sensitive, high-threshold L-type Ca²⁺ channel currents which were dihydropyridine-sensitive and blocked by Cd²⁺, but the activation kinetics were about 100 times slower than expected for skeletal muscle Ca²⁺ channel currents. This could have been due to the cell type in which α₁ , was being expressed or to the lack of a regulatory component particularly one of the subunits that copurifies with α₁. We show here that coexpression of skeletal muscle β with skeletal muscle α₁, generates cell lines expressing Ca²⁺ channel currents with normal activation kinetics as evidence for the participation of the dihydropyridine-receptor β subunits in the generation of skeletal muscle Ca²⁺ channel currents.