Modulation of the α1A Ca2+ channel by β subunits at physiological Ca2+ concentration

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Abstract
The class A Ca2+ channel αl subunit (αlA) was expressed in Xenopus oocytes alone or in combination with the βlb, β2a, β3, or β4 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, were strongly modulated by the nature of the co‐expressed β subunit. On the other hand, for each combination, the kinetics of inactivation were similar in 1.8 mM Ca2+ and 40 mM Ba2+ (for example co‐expression of the β2a subunit reduced inactivation using either 40 mM Ba2+ or 1.8 mM Ca2+). Thus, modulation of channel properties by the β subunit is different in physiological Ca2+ or high Ba2+ concentrations. These results must be taken into consideration to extrapolate the role of the β subunit in native cells.