INTRACELLULAR DIALYSIS OF CYCLIC-NUCLEOTIDES INDUCES INWARD CURRENTS IN TURTLE VOMERONASAL RECEPTOR NEURONS

Turtle vomeronasal receptor neurons in slice preparations were studied using the patch-clamp technique in the whole-cell and cell-attached c onfigurations. The mean resting potential was -48, and the response to an injected current step consisted of either a single spike or a trai n of spikes. An injected current of 3-30 pA was required to depolarize the neuron to spike threshold near -50 mV, Voltage-clamped vomeronasa l receptor neurons displayed transient inward currents followed by sus tained outward currents in response to depolarizing voltage steps. In cell-attached recordings, 10 mu M forskolin added to the bath caused a transient increase of spike rate. Intracellular application of cAMP e voked an inward current in a dose-dependent manner from the neurons vo ltage clamped at -70 mV; 0.1 mM cAMP was sufficient to elicit an inwar d current in the neurons. The magnitude of the response to cAMP reache d a plateau at 1 mM with an average peak amplitude of 176 +/- 34 pA. I ntracellular application of 1 mM cGMP also evoked an inward current wi th an average peak amplitude of 227 +/- 61 pA. The reversal potentials of the induced components were estimated to be 10 +/- 7 mV for cAMP a nd -4 +/- 16 mV for cGMP. The reversal potential of the cAMP-induced c urrent in external Cl--free solution was similar to that in normal Rin ger's solution, suggesting that Cl- current is not significantly invol ved in the current. The present results represent the first evidence o f cyclic nucleotide-activated conductance in the vomeronasal receptor membranes.