Nicotinic acetylcholine currents of cultured Kkenyon cells from the mushroom bodies of the honey bee Aapis mellifera.

Abstract

1. Acetylcholine-induced currents of mushroom body Kenyon cells from the honey bee Apis mellifera were studied using the whole-cell configuration of the patch clamp technique. Pressure application of 1 mM acetylcholine (ACh) induced inward currents with amplitudes between -5 and -500 pA. 2. The cholinergic agonists ACh and carbamylcholine had almost equal potencies of current activation at concentrations between 0.01 and 1 mM; nicotine was less potent. The muscarinic agonist oxotremorine did not elicit any currents. 3. Approximately 80 % of the ACh-induced current was irreversibly blocked by 1 microM alpha-bungarotoxin. Atropine (1 mM) did not block the ACh-induced current. 4. Upon prolonged ACh application the current desensitized with a time course that could be approximated by the sum of two exponentials (tau1 = 276 +/- 45 ms (mean +/- s.e.m. ) for the fast component and tau2 = 2.4 +/- 0.7 s for the slow component). 5. Noise analyses of whole-cell currents yielded elementary conductances of 19.5 +/- 2.4 pS for ACh and 23.7 +/- 5.0 pS for nicotine. The channel lifetimes, calculated from the frequency spectra, were tauo = 1.8 ms for ACh and tauo = 2.5 ms for nicotine. 6. Raising the external calcium concentration from 5 to 50 mM shifted the reversal potential of the ACh-induced current from +4. 6 +/- 0.9 to +37.3 +/- 1.3 mV. The calcium-to-sodium permeability ratio (PCa : PNa) was 6.4. 7. In high external calcium solution (50 mM) the ACh-induced current rectified in an outward direction at positive membrane potentials. 8. We conclude that Kenyon cells express nicotinic ACh receptors with functional profiles reminiscent of the vertebrate neuronal nicotinic ACh receptor subtype.