Modulation of the skeletal muscle sodium channel α-subunit by the β₁ -subunit

Co-expression of cloned sodium channel β₁ -subunit with the rat skeletal muscle-subunit (α_μI) accelerated the macroscopic current decay, enhanced the current amplitude, shifted the steady state inactivation curve to more negative potentials and decreased the time required for complete recovery from inactivation. Sodium channels expressed from skeletal muscle mRNA showed a similar behaviour to that observed from α_μI β₁, indicating that β₁ restores 'physiological' behaviour. Northern blot analysis revealed that the Na⁺ channel β₁-subunit is present in high abundance (about 0.1%) in rat heart, brain and skeletal muscle, and the hybridization with untranslated region of the 'brain' β₁ cDNA to skeletal muscle and heart mRNA indicated that the diffferent Na ⁺ channel α-subunits in brain, skeletal muscle and heart may share a common β₁ -subunit.