INOSITOL-1,4,5-TRISPHOSPHATE INDUCES RESPONSES IN RECEPTOR NEURONS INRAT VOMERONASAL SENSORY SLICES

Using the whole-cell mode of the patch-clamp technique, we recorded ac tion potentials, voltage-activated cationic currents and putative seco nd messenger-activated currents in receptor neurons in the vomeronasal sensory epithelium of female rats. The resting membrane potential and input resistance were -45.5 +/- 2.5 mV (mean +/- SEM, n = 39) and 1.5 +/- 0.2 G Omega (mean +/- SEM, n = 37). Current injection of 1-3 pA i nduced overshooting action potentials. The firing frequency increased with increasing current injections linearly from 1 to 10 pA and reache d a plateau at 30 pA, suggesting that rat vomeronasal receptor neurons sensitively elicit action potentials in response to a small receptor potential. Under voltage clamp, voltage-dependent Na+ inward current, inward Ca2+ current, sustained outward Kt current and Ca2+-activated K +-current were identified. Dialysis of D-inositol-1,4,5-trisphosphate (D-IP3) induced inward currents with an increase in membrane conductan ce in similar to 54% of the cells and inward current fluctuations in 1 5% of the cells. L-IP3 also induced inward currents and current fluctu ations in 53 and 13% of the cells respectively. The mean amplitude of inward currents induced by 100 mu M D-IP3 and L-IP3 were 84.6 +/- 14.0 pA (SEM, n = 82) and 66.1 +/- 9.4 pA (SEM, n = 100) respectively The IP3-induced responses were blocked by elimination of Naf and Ca2+ in t he external solution or application of 10 mu M ruthenium red. The pres ent:study suggested that IP3-mediated transduction pathways exist in r at vomeronasal receptor neurons.