INOSITOL 1,4,5-TRISPHOSPHATE-GATED CONDUCTANCE IN ISOLATED RAT OLFACTORY NEURONS

1. The effect of intracellular application of inositol 1,4,5-trisphosp hate (IP3) from the patch pipette was analyzed in isolated rat olfacto ry neurons under whole-cell patch clamp. 2. Intracellular dialysis of 10 mu M 1,4,5-IP3 in K+-internal solution induced a sustained depolari zation of 35.8 +/- 10.5 (SD) mV (n = 16). The IP3-induced response was observed in 75% of the cells dialyzed with I-P3, but not when 10 mu M ruthenium red was also included in the pipette solution (4 cells). Lo wer concentrations (50-100 nM) of 2,4,5-IP3 induced similar responses to those produced by 1,4,5-IP3 in five of eight olfactory neurons. 3. Steady-state I-V relationships of IP3-gated currents with K+-internal solution were classified into two types: outwardly rectifying and N-sh aped. In Cs+-internal solution outwardly rectifying and linear pattern s were observed. 4. The IP3-induced currents were inhibited by externa l Cd2+ ( 1 mM): The reversal potentials of the Cd2+-inhibitable curren ts were -16.1 mV (n = 2) and -29.0 +/- 7.1 mV (n = 3) for the outwardl y rectifying and N-shaped types, respectively, in K+-internal solution . The reversal potential was -5.9 +/- 6.8 mV(n = 5) in the Cs+-interna l solution. 6. In contrast, the Ca2+-ionophore, ionomycin(5 mu M) hype rpolarized the olfactory neurons and greatly potentiated the outward c urrents at positive holding membrane potential. 7. The data suggest th at IP3 can depolarize rat olfactory neurons without mediation by intra cellular Ca2+.