Responsiveness of vomeronasal cells to a newt peptide pheromone, sodefrin as monitored by changes of intracellular calcium concentrations

A peptide pheromone of the red-bellied male newt, sodefrin was tested for its ability to increase intracellular concentrations of Ca2+ ([Ca2+]i) in the dissociated vomeronasal (VN) cells of females by means of calcium imaging system. The pheromone elicited a marked elevation of [Ca2+]i in a small population of VN cells from sexually developed females. The population of cells exhibiting sodefrin-induced elevation of [Ca2+]i increased concentration-dependently. A pheromone of a different species was ineffective in this respect. The VN cells from non-reproductive females or from reproductive males scarcely responded to sodefrin in terms of elevating [Ca2+]i. In the cells from hypophysectomized and ovariectomized females, the sodefrin-inducible increase of [Ca2+]i never occurred. The cells from the operated newts supplemented with prolactin and estradiol exhibited [Ca2+]i responses to sodefrin with a high incidence. Thus, sex- and hormone-dependency as well as species-specificity of the responsiveness of the VN cells to sodefrin was evidenced at the cellular level. Subsequently, possibility of involvement of phospholipase C (PLC)-inositol 1,4,5-trisphosphate (IP3) and/or PLC-diacylglycerol (DAG)-protein kinase C (PKC) pathways in increasing [Ca2+]i in VN cells in response to sodefrin was explored using pharmacological approaches. The results indicated that PLC is involved in generating the Ca2+ signal in all sodefrin-responsive VN cells, whereas IP3 in approximately 50% of the cells and DAG-PKC in the remaining cells. In the latter case, the increase of [Ca2+]i was postulated to be induced by the influx of Ca2+ through the L-type channel. The significance of the finding is discussed.