NEURAL EFFECTS OF PARATHYROID-HORMONE - MODULATION OF THE CALCIUM-CHANNEL CURRENT AND METABOLISM OF MONOAMINES IN IDENTIFIED HELISOMA SNAILNEURONS

Neuronal effects of parathyroid hormone (PTH) have been reported in ve rtebrates. The effect of PTH on invertebrate central neurons within th e buccal ganglion of Helisoma trivolvis snails was examined in the pre sent study. By using a vibrating probe, PTH was found to induce a tran sient calcium-dependent inward current in intact buccal ganglia. Intra cellular microelectrode recording revealed that PTH broadened the spon taneous action potential in buccal B5 neurons in situ. By using the wh ole-cell configuration of the patch-clamp technique, PTH was demonstra ted to increase the N-like calcium channel currents in isolated B5 neu rons in a concentration-dependent manner. This effect of PTH on the N- like calcium channel currents depended on the activation of a G protei n insensitive to pertussis toxin, but was unlikely to be mediated by t he cyclic AMP dependent protein kinase. Furthermore, the release of ga mma-glutamyl conjugate of dopamine from buccal ganglia was selectively increased in the presence of PTH. These results represent the first d emonstration that a vertebrate peptide hormone, PTH, selectively modul ates the N-like voltage-dependent calcium channel currents in identifi ed invertebrate neurons. Therefore, a novel role of PTH in the regulat ion of invertebrate central neural functions is indicated.