Chemosensitive conductance and inositol 1,4,5-trisphosphate-induced conductance in snake vomeronasal receptor neurons

Snake vomeronasal receptor neurons in slice preparations were studied using the patch-clamp technique in the conventional and nystatin-perforated whole-cell configurations. The mean resting potential was approximately -70 mV; the average input resistance was 3 G Omega. Neurons required current injection of only 1-10 pA to display a variety of spiking patterns. Intracellular dialysis of 100 mu M inositol 1,4,5-trisphosphate (IP3) evoked an inward current in 38% of neurons, with an average peak amplitude of 16.4 +/- 2.8 pA at a holding potential of -70 mV. Application of 100 mu M 3-deoxy-3-fluoro-D-myo-inositol 1,4,5-trisphosphate (F-IP3), a derivative of IP3, also evoked an inward current in 4/8 (50%) neurons (32.6 +/- 58 pA at -70 mV, n = 4). The reversal potentials of the induced components were estimated to be -14 +/- 5 mV for IP3 and -17 +/- 3 mV for F-IP3. Bathing the neurons in 10 mu M ruthenium red solution greatly reduced the IP3-evoked inward current to 1.6 +/- 1.1 pA at -70 mV (n = 6). With Cs+-containing internal solution, neither the Ca2+-ATPase inhibitor thapsigargin (1-50 mu M) nor the Ca2+-ionophore ionomycin (10 mu M) evoked a significant current response, suggesting that IP3 can elicit current response in the neurons without mediation by intracellular Ca2+ stores. Intracellular application of 1 mM cAMP evoked no detectable current response. Extracellular application of chemoattractant for snakes evoked a very large inward current. The reversal potential of the chemoattractant-induced current was similar to that of the IP3-induced current. The present results suggest that IP3 may act as a second messenger in the transduction of chemoattractants in the garter snake vomeronasal organ.