Inhibition of calcium currents in cultured myenteric neurons by neuropeptide Y: evidence for direct receptor/channel coupling

Single channel recordings from rat myenteric plexus neurons demonstrated the presence of two categories of Ca²⁺ channels. One type of Ca channel had a slope conductance of 27 pS and was sensitive to dihydropyridines while the other type had a conductance of 14 pS and was dihydropyridine-insensitive. The 14 pS channel was mostly inactivated at a holding potential of -40 mV, while the 27 pS channel was much more resistant to depolarized holding potentials. A majority of whole-cell current was reprinted by the use of negative holding (-90 mV) potentials, when compared to that obtained at a holding potential of -40 mV. These properties are consistent with N- and L-type Ca channels previously described. In general, the inactivating part of the whole-cell Ca²⁺ current, selectively reprimed by negative holding potentials, was inhibited by neuropeptide Y (NPY). Depolarization-induced [Ca²⁺]_i transients assessed using fura-2 showed that the inhibitory effects of nitrendipine and NPY were additive. The effects of NPY were abolished by pertussis toxin pretreatment. Single-channel experiments showed that neither the 14 nor the 27 pS Ca channel currents were inhibited by the addition of NPY outside the patch pipette. These results suggest that NPY modulates N-type Ca²⁺ channels selectively in these neurons and that an easily diffusible second messenger does not appear to participate in receptor/channel coupling.