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

摘要

The β1a subunit, one of the auxiliary subunits of CaV1.1 channels, was expressed in COS-1 cells, purified by electroelution and electrodialysis techniques and identified by Western blot using monoclonal antibodies. The purified β1a subunit strongly interacted in vitro with the alpha interaction domain (AID) of CaV1.1 channels. The actions of the purified β1a subunit on CaV1.1 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+ (IBa). Values of peak IBa were doubled by the β1a subunit in frog and mouse muscle vesicles and the amplitude of the slow component of tail currents was greatly increased. The actions of the β1a subunit on CaV1.1 channel currents reached a steady state within 20 min. The β1a subunit had no effect on the time courses of activation or inactivation of IBa 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: Qmax + 28.0 ± 6.6 nC μF−1, V + −58.0 ± 2.0 mV and k + 15.3 ± 1.1 mV (n = 24). In the presence of the β1a subunit, these parameters remained unchanged: Qmax + 29.8 ± 3.5 nC μF−1, V + −54.5 ± 2.2 mV and k + 16.4 ± 1.3 mV (n = 21). Overall, the work describes a novel preparation to explore in situ the role of the β1a subunit on the function of adult CaV1.1 channels.