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The peptides neuropeptide Y (NPY) and bradykinin (BK) both inhibited Ca*+ 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, a,(M,, 39kd) and oiz (M,, 40 kd). We examined the ability of three purified bovine a subunits (identified with antibodies as a,, oil, and ui2) to reconstitute the inhibitory effects of NPY and BK. Reconstitution of NPY effects occurred according to the potency series o,> uir>> aiz. However, in the case of BK all three C proteins were approximately equally effective. Whereas complete reconstitution of NPY effects could be obtained with ao, no single a subunit produced complete reconstitution of BK. Combinations of a, and uiz, however, were able to completely reconstitute the effects of BK. Thus several C …