ROLE OF DOMAIN-I OF NEURONAL CA2-1 SUBUNITS IN G-PROTEIN MODULATION( CHANNEL ALPHA)

1. We studied the G protein inhibition of heteromultimeric neuronal Ca 2+ channels by constructing a series of chimeric channels between the strongly modulated alpha 1B subunit and the alpha 1E(rbEII) subunit, w hich showed no modulation. 2. In parallel studies, alpha 1 subunit con structs were co-expressed together with the accessory Ca2+ channel alp ha 2-delta and beta 2a subunits in mammalian (COS-7) cells and Xenopus oocytes. G protein inhibition of expressed Ca2+ channel currents was induced by co-transfection of G beta 1 and G gamma 2 subunits in COS-7 cells or activation of co-expressed dopamine (D2) receptors by quinpi role (100 nM) in oocytes. 3. The data indicate that transfer of the al pha 1B region containing the N-terminal, domain I and the I-II loop (i .e. the alpha 1B(1-483) sequence), conferred G protein modulation on a lpha 1E(rbEII), both in terms of a slowing of activation kinetics and a reduction in current amplitude. 4. In contrast, the data are not con sistent with the I-II loop and/or the C-terminal forming a unique site for G protein modulation.