The β1a subunit regulates the functional properties of adult frog and mouse L-type Ca2+ channels of skeletal muscle

The beta(1a) subunit, one of the auxiliary subunits of Ca(V)1.1 channels, was expressed in COS-1 cells, purified by electroelution and electrodialysis techniques and identified by Western blot using monoclonal antibodies. The purified beta(1a) subunit strongly interacted in vitro with the alpha interaction domain (AID) of Ca(V)1.1 channels. The actions of the purified beta(1a) subunit on Ca(V)1.1 channel currents were assessed in whole cell voltage clamp experiments performed in vesicles derived from frog and mouse adult skeletal muscle plasma membranes. L-type inward currents were recorded in solutions containing Ba2+(I-Ba). Values of peak I-Ba were doubled by the,beta(1a) subunit in frog and mouse muscle vesicles and the amplitude of the slow component of tail currents was greatly increased. The actions of the, beta(1a) subunit on Ca(V)1.1 channel currents reached a steady state within 20 min. The beta(1a) subunit had no effect on the time courses of activation or inactivation of I-Ba or shifted the current-voltage relation. Non-linear capacitive currents were recorded in solutions that contained mostly impermeant ions. Charge movement depended on voltage with average Boltzmann parameters: Q(max) = 28.0 +/- 6.6 nC muF(-1), V = -58.0 +/- 2.0 mV and k = 15.3 +/- 1.1 mV (n = 24). In the presence of the,, subunit, these parameters remained unchanged: Q(max) = 29.8 +/- 3.5 nC muF(-1), V = -54.5 +/- 2.2 mV and k = 16.4 +/- 1.3 mV (n = 2 1). Overall, the work describes a novel preparation to explore in situ the role of the, beta(1a) subunit on the function of adult Ca(V)1.1 channels.