COMPARISON OF NEURONAL NICOTINIC RECEPTORS IN RAT SYMPATHETIC NEURONSWITH SUBUNIT PAIRS EXPRESSED IN XENOPUS OOCYTES

1. The agonist sensitivity of nicotinic acetylcholine receptors in rat superior cervical ganglion (SCG) neurones was compared with that of c loned receptors expressed in Xenopus oocytes by pairwise injections of alpha 3-beta 2 or alpha 3-beta 4 neuronal nicotinic subunit combinati ons. 2. Agonist responses in rat SCG neurones indicated that cytisine was the most potent agonist and lobeline the least potent (rank order of potency: cytisine > dimethylphenyl- piperazinium iodide (DMPP) > ni cotine > ACh > carbachol > lobeline). 3. Receptors expressed in oocyte s by injection of alpha 3 and beta 2 subunits had a relatively high se nsitivity to DMPP and low sensitivity to cytisine (rank order of poten cy: DMPP > ACh > lobeline > carbachol > nicotine > cytisine), whereas receptors composed of alpha 3 and beta 4 subunits had a high sensitivi ty to cytisine and low sensitivity to DMPP (rank order of potency: cyt isine > nicotine approximate to ACh > carbachol > lobeline). 4. With t he exception of responses to DMPP, agonist sensitivity measurements su ggest that nicotinic receptors in the rat SCG are composed of alpha 3 and beta 4 subunits. The results are discussed in terms of the recepto r subunit mRNAs known to be expressed in the rat SCG and previous evid ence of functional heterogeneity of rat SCG nicotinic acetylcholine re ceptors.