Comparison of a Ca(2+)-gated conductance and a second-messenger-gated conductance in rat olfactory neurons

The effect of a rise in intracellular Ca(2+) concentration was analyzed in isolated rat olfactory neurons using a whole-cell patch-clamp technique. Intracellular dialysis of 1 mmol l(-)(1) Ca(2+) in a standard-K(+), low-Cl(-) internal solution (E(Cl)=-69 mV) from the patch pipette into the olfactory neurons induced a sustained outward current of 49+/-5 pA (N=13) at -50 mV in all the cells examined. The outward currents were inhibited by external application of 100 micromol l(-)(1) 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB). External application of a Ca(2+) ionophore, 3 micromol l(-)(1) ionomycin, induced an inward current in three of eight cells whose voltages were clamped using the gramicidin-perforated technique, but ionomycin elicited an outward current in the other five cells, suggesting that natural intracellular Cl(-) concentration in the olfactory neurons was heterogeneous. While intracellular dialysis of 50 micromol l(-)(1) inositol 1,4,5-trisphosphate (1,4,5-InsP(3)) in the standard-K(+), low-Cl(-) internal solution induced the NPPB-sensitive outward current in 31 % of cells, and 500 micromol l(-)(1) cAMP induced it in 21 % of cells, a large proportion of the cells displayed an inward current in response to 1,4,5-InsP(3) and cAMP. The results suggest that 1,4,5-InsP(3) and cAMP can elicit Ca(2+)-dependent Cl(-) conductance and Ca(2+)-independent cation conductance in rat olfactory neurons.