Voltage-activated currents from adult honeybee (Apis mellifera) antennal motor neurons recorded in vitro and in situ.

Abstract

Voltage-activated currents from adult honey bee antennal motor neurons were characterized with in vitro studies in parallel with recordings taken from cells in situ. Two methods were used to ensure unequivocal identification of cells as antennal motor neurons: 1) selective backfilling of the neurons with fluorescent markers before dissociation for cell culture or before recording from cells in intact brains, semiintact brains, or in brain slices or 2) staining with a fluorescent marker via the patch pipette during recordings and identifying antennal motor neurons in situ on the basis of their characteristic morphology. Four voltage-activated currents were isolated in these antennal motor neurons with pharmacological, voltage, and ion substitution protocols. The neurons expressed at least two distinct K+ currents, a transient current (IA) that was blocked by 4-aminopyridine (4-5 x 10(-3) M), and a sustained current (IK(V)) that was partially blocked by tetraethylammonium (2-3 x 10(-2) M) and quinidine (5 x 10(-5) M). IA activated above -40 to -30 mV and the half-maximal voltages for steady-state activation and inactivation were -8.8 and -43.2 mV, respectively. IK(V) activated above -50 to -40 mV and the midpoint of the steady-state activation curve was +11.2 mV. IK(V) did not show steady-state inactivation. Additionally, two inward currents were isolated: a tetrodotoxin (10(-7) M)-sensitive, transient Na+ current (INa) that activated above -35 mV, with a maximum around -5 mV and a half-maximal voltage for inactivation of -72.6 mV, and a CdCl2 (5 x 10(-5) M)-sensitive Ca2+ current that activated above -45 to -40 mV, with a maximum around -15 mV. This study represents the first step in our effort to analyze the cellular and ionic mechanisms underlying the intrinsic properties and plasticity of antennal motor neurons.