Modulation of the alpha 1A Ca2+ channel by beta subunits at physiological Ca2+ concentration

The class A Ca2+ channel alpha 1 subunit (alpha 1A) mas expressed in Xenopus oocytes alone or in combination with the beta 1b, beta 2a, beta 3, or beta 4 subunit, Analysis of voltage-dependent activation and inactivation in the presence of 1.8 mM external Ca2+ showed an hyperpolarising shift of both relations when compared to similar recordings performed in the presence of 40 mM Ba2+. These shifts, which differed for activation and inactivation, mere strongly modulated by the nature of the co-expressed beta subunit, On the other hand, for each combination, the kinetics of inactivation were similar in 1.8 mM Ca2+ and 30 mM Ba2+ (for example co-expression of the beta 2a subunit reduced inactivation using either 40 mM Ba2+ or 1.8 mM Ca2+), Thus, modulation of channel properties by the beta subunit is different in physiological Ca2+ or high Ba2+ concentrations. These results must be taken into consideration to extrapolate the role of the beta subunit in native cells.