HETEROGENEITY OF NICOTINIC RECEPTOR CLASS AND SUBUNIT MESSENGER-RNA EXPRESSION AMONG INDIVIDUAL PARASYMPATHETIC NEURONS FROM RAT INTRACARDIAC GANGLIA

Neurons have the potential to form thousands of distinct neuronal nico tinic receptors from the eight alpha and three beta subunits that curr ently are known. In an effort to determine how much of this potential complexity is realized among individual neurons, we examined the nicot inic pharmacological and biophysical properties and receptor subunit m RNA expression patterns in individual neurons cultured from rat epicar dial ganglia. Analysis of the whole-cell pharmacology of these neurons showed a diversity of responses to the agonists acetylcholine, nicoti ne, cytisine, and 1,1-dimethyl-4-phenylpiperazinium, suggesting that a heterogeneous population of nicotinic receptor classes, or subtypes, is expressed by individual neurons. Single-channel analysis demonstrat ed three distinct conductances (18, 24, and 31 pS), with patches from different neurons containing different combinations of these channel c lasses. We used single-cell RT-PCR to examine nicotinic acetylcholine receptor (nAChR) subunit mRNA expression by individual neurons. Althou gh mRNAs encoding all eight neuronal nAChR subunits for which we probe d (alpha 2-alpha 5, alpha 7, beta 2-beta 4) were present in multicellu lar cultures, we found that individual epicardial neurons express dist inct subsets of these nAChR subunit mRNAs. These results suggest that individual epicardial neurons express distinct arrays of nAChR subunit s and that these subunits may assemble into functional receptors with distinct and variable subunit composition. This variable receptor subu nit expression provides an explanation for the diversity of pharmacolo gical and single-channel responses we have observed in individual neur ons.