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 GΩ. Neurons required current injection of only 1–10 pA to display a variety of spiking patterns. Intracellular dialysis of 100 μM inositol 1,4,5-trisphosphate (IP[sub 3]) evoked an inward current in 38% of neurons, with an average peak amplitude of 16.4 ± 2.8 pA at a holding potential of –70mV. Application of 100 μM 3-deoxy-3-fluoro- d- myo-inositol 1,4,5-trisphosphate (F-IP[sub 3]), a derivative of IP[sub 3], 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 IP[sub 3] and –17 ± 3 mV for F-IP[sub 3]. Bathing the neurons in 10 μM ruthenium red solution greatly reduced the IP[sub 3]-evoked inward current to 1.6 ± 1.1 pA at –70 mV ( n = 6). With Cs[sup +]-containing internal solution, neither the Ca[sup 2+]-ATPase inhibitor thapsigargin (1–50 μM) nor the Ca[sup 2+]-ionophore ionomycin (10 μM) evoked a significant current response, suggesting that IP[sub 3] can elicit current response in the neurons without mediation by intracellular Ca[sup 2+] 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 IP[sub 3]-induced current. The present results suggest that IP[sub 3] may act as a second messenger in the transduction of chemoattractants in the garter snake vomeronasal organ. [ABSTRACT FROM AUTHOR]