ATP modulates intracellular Ca2+ and firing rate through a P2Y1 purinoceptor in cane toad pacemaker cells

Bipolar sensory neurons within the vomeronasal organ (VNO) are thought to mediate the detection of pheromones in vertebrates. In the mouse, VNO neurons respond to pheromones with a rise in intracellular Ca²⁺ that accompanies a depolarization of the cell. Transduction of the pheromone appears to occur through the activation of a phosphatidylinositol signalling pathway, but the ion channels that respond to this signalling pathway have not been identified. In this report patch-clamp recording from hamster vomeronasal sensory neurons was used to identify second-messenger-gated channels that might play a role in transduction. The results demonstrate that VNO neurons show abundant expression of a Ca^2+-activated non-selective (CaNS) cation channel. The CaNS channel does not discriminate between Na⁺ and K⁺ and has a slope conductance of 22 pS. Half-activation of the channel occurs at a Ca²⁺ concentration of 0.5 m m (at -80 mV). The probability of opening ( P _o) of the channel is further augmented at positive potentials, and shows an e-fold voltage dependence per 37 mV. The channel exhibits rapid rundown following patch excision with P _o decreasing from near 1.0 to near 0. The adenine nucleotides ATP and cAMP block the channel with an apparent affinity of 3 and 42 μ m , respectively (-80 mV). Both the activation of the channel by Ca²⁺ and the block of the channel by adenine nucleotides show a mild voltage dependence, which can be accounted for by the voltage dependence of P _o. The properties of this channel make it a candidate to either directly mediate vomeronasal sensory transduction, or to amplify the primary sensory response.