Apical and basal neurones isolated from the mouse vomeronasal organ differ for voltage-dependent currents

The mammalian vomeronasal organ (VNO) contains specialized neurones that transduce the chemical information related to pheromones into discharge of action potentials to the brain. Molecular and biochemical studies have shown that specific components of the pheromonal transduction systems are segregated into two distinct subsets of vomeronasal neurones: apical neurones and basal neurones. However, it is still unknown whether these neuronal subsets also differ in other functional characteristics, such as their membrane properties. We addressed this issue by studying the electrophysiological properties of vomeronasal neurones isolated from mouse VNO. We used the patch-clamp technique to examine both the passive membrane properties and the voltage-gated Na+, K+ and Ca2+ currents. Apical neurones were distinguished from basal ones by the length of their dendrites and by their distinct immunoreactivity for the putative pheromone receptor V2R(2). The analysis of passive properties revealed that there were no significant differences between the two neuronal subsets. Also, apical neurones were similar to basal neurones in their biophysical and pharmacological properties of voltage-gated Na+ and K+ currents. However, we found that the density of Na+ currents was about 2-3 times greater in apical neurones than in basal neurones. Consistently, in situ hybridization analysis revealed a higher expression of the Na+ channel subtype III in apical neurones than in basal ones. In contrast, basal neurones were endowed with Ca2+ currents (T-type) of greater magnitude than apical neurones. Our findings indicate that apical and basal neurones in the VNO exhibit distinct electrical properties. This might have a profound effect on the sensory processes occurring in the VNO during pheromone detection.