The inhibition of [125I]omega-conotoxin GVIA binding to neuronal membranes by neomycin may be mediated by a GTP-binding protein.

omega-Conotoxin GVIA (omega-CT) has been reported to block calcium currents at the L- and N-type calcium channels. In neuronal membranes omega-CT, and the aminoglycoside antibiotic neomycin, have been shown to inhibit [125I]omega-CT binding, presumably acting at the N-type calcium channel. We demonstrate here that the concentration curve for neomycin sulfate inhibition of [125I]omega-CT binding is shifted to the right by GTP analogues or fluoride, increasing the IC50 for neomycin. [125I]omega-CT binding is unaffected by these agents and in competition studies the potency of omega-CT, Ca2+, or La3+ is not modulated by GTP analogues or fluoride. These results indicate that the inhibition of [125I]omega-CT binding by neomycin may be mediated by a GTP binding protein.