Nicotinic acetylcholine currents of cultured Kenyon cells from the mushroom bodies of the honey bee Apis mellifera

1. Acetylcholine-induced currents of mushroom body Kenyon cells from the ho ney bee Apis mellifera were studied using the whole-cell configuration of t he 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 potenc ies of current activation at concentrations between 0.01 and 1 mM; nicotine was less potent. The muscarinic agonist oxotremorine did not elicit any cu rrents. 3. Approximately 80% of the ACh-induced current was irreversibly blocked by 1 mu M alpha-bungarotoxin. Atropine(1, mM ) did not block the ACh-induced current. 4. Upon prolonged ACh application the current desensitized with a time cour se that could be approximated by the sum of two exponentials tau(1) = 276./- 45 ms (mean +/- S.E.M.) for the fast component and (tau(2) = 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 life times, calculated from the frequency spectra, were tau(o) = 1.8 ms for ACI 1 and tau(1) = 2.5 ms for nicotine. 6. Raising the external calcium concentration from 5 to 50 mM shifted the r eversal potential of the ACh-induced current from +4.6 +/- 0.9 to +37.3 +/- 1.3 mV. The calcium-to-sodium permeability ratio (P-Ca: P-Na) was 6 4. 7. In high external calcium solution (50 mM) the ACh-induced current rectif ied in an outward direction at positive membrane potentials. 8. We conclude that Kenyon cells express nicotinic ACh receptors with funct ional profiles reminiscent of the vertebrate neuronal nicotinic ACh recepto r subtype.