EXPRESSION OF BETA-SUBUNIT MODULATES SURFACE-POTENTIAL SENSING BY CALCIUM CHANNELS

We have expressed the alpha(1A) calcium channel subunit alone, and in combination with different beta subunits, and investigated the effect of the external Ba2+ concentration on the voltage dependence of activa tion. Increasing the external Ba2+ concentration from 2.5 to 40 mM ind uced in all cases a depolarising shift of the potential for half-activ ation. The magnitude of this shift however, was different depending on whether the alpha(1A) subunit was expressed alone or with a beta subu nit. Consistently, calculated external surface-charge density and pote ntial were larger when a beta subunit was expressed. These results sug gest that expression of an auxiliary subunit can influence calcium cha nnel gating by modifying the sensitivity of the voltage sensor to the membrane potential profile.