Voltage- and calcium-activated currents in cultured olfactory receptor neurons of male mamestra brassicae (lepidoptera)

Abstract

Insect olfactory receptor neurons (ORNs) grown in primary cultures were studied using the patch-clamp technique in both conventional and amphotericin B perforated whole-cell configurations under voltage-clamp conditions. After 10-24 days in vitro, ORNs had a mean resting potential of -62 mV and an average input resistance of 3.2 GΩ. Five different voltage-dependent ionic currents were isolated: one Na+, one Ca2+ and three K+ currents. The Na+ current (35-300 pA) activated between -50 and -30 mV and was sensitive to 1 μM tetrodotoxin (TTX). The sustained Ca2+ current activated between -30 and -20 mV, reached a maximum amplitude at 0 mV (-4.5 ± 6.0 pA) that increased when Ba2+ was added to the bath and was blocked by 1 mM Co2+. Total outward currents were composed of three K+ currents: a Ca2+-activated K+ current activated between -40 and -30 mV and reached a maximum amplitude at +40 mV (605 ± 351 pA); a delayed-rectifier K+ current activated between -30 and -10 mV, had a mean amplitude of 111 ± 67 pA at +60 mV and was inhibited by 20 mM tetraethylammonium (TEA); and, finally, more than half of ORNs exhibited an A-like current strongly dependent on the holding potential and inhibited by 5 mM 4-aminopyridine (4-AP). Pheromone stimulation evoked inward current as measured by single channel recordings.