The peptides neuropeptide Y (NPY) and bradykinin (BK) both inhibited Ca2+ currents in rat dorsal root ganglion neurons (DRG) in vitro. The effects of both peptides were completely blocked by treatment of cells with pertussis toxin. Based on antigenic determinants, DRG cells contained at least two pertussis toxin substrates, αo (Mr, 39kd) and αi2 (Mr 40 kd). We examined the ability of three purified bovine α subunits (identified with antibodies as αo, α1, and α2) to reconstitute the inhibitory effects of NPY and BK. Reconstitution of NPY effects occurred according to the potency series αo>αi1≫αi2. However, in the case of BK all three G proteins were approximately equally effective. Whereas complete reconstitution of NPY effects could be obtained with αo, no single a subunit produced complete reconstitution of BK. Combinations of αo and αi2, however, were able to completely reconstitute the effects of BK. Thus several G proteins can effect the regulation of Ca2+ channels in these cells. However, neurotransmitters may be selective in the G proteins or combinations of G proteins utilized to achieve this regulation.
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