A NICOTINIC ACETYLCHOLINE-RECEPTOR SUBUNIT FROM INSECT BRAIN FORMS A NONDESENSITIZING HOMOOLIGOMERIC NICOTINIC ACETYLCHOLINE-RECEPTOR WHEN EXPRESSED IN XENOPUS OOCYTES

The locust alpha-like nicotinic receptor subunit alpha L1 was expressed in Xenopus oocytes. Small but reproducible currents were elicited by application of high concentrations of nicotine, demonstrating that alpha L1 is capable of forming homo-oligomeric channels. Nicotine-evoked currents were blocked by alpha-bungarotoxin and methyllycaconitine. Comparison with chick alpha 7 receptors showed that the two receptors differ with respect to nicotine sensitivity and timecourse of evoked currents. Nicotine dose-response curves gave EC(50) values of 24 and 830 mu M for alpha 7 and alpha L1 respectively. Whereas alpha 7 responses showed characteristic fast onset and rapid desensitization within 3 s, alpha L1 currents displayed a slow onset and showed no tendency to desensitize during 45 s of agonist application. Thus alpha L1 is a novel nicotinic subunit for the further exploration of structure-function relationships of ligand-gated ion channels. The question of the subunit composition of native insect receptors remains open.