ROLES OF A MEMBRANE-LOCALIZED BETA-SUBUNIT IN THE FORMATION AND TARGETING OF FUNCTIONAL L-TYPE CA2+ CHANNELS

We report several unexpected findings that provide novel insights into the properties and interactions of the alpha(1) and beta subunits of dihydropyridine-sensitive L-type channels, First, the beta(2a) subunit was expressed as multiple species of 68-72 kDa; the 70-72-kDa species arose from post-translational modification, Second, cell fractionatio n and immunocytochemical studies indicated that the hydrophilic beta(2 a) subunit, when expressed alone, was membrane-localized, Third, the b eta(2a) subunit increased the membrane localization of the alpha(1) su bunit and the number of cells expressing L-type Ca2+ currents, without affecting the total amount of the expressed alpha(1C) subunit. Expres sion of maximal currents in alpha(1C)/beta(2a) co-transfected cells pa ralleled the time course of expression of the beta subunit. Taken toge ther, these results suggest that the beta subunit plays multiple roles in the formation, stabilization, targeting, and modulation of L-type channels.