COEXPRESSION OF 4 MUSCARINIC RECEPTOR GENES BY THE INTRINSIC NEURONS OF THE RAT AND GUINEA-PIG HEART

Expression of the messenger RNAs encoding the five different muscarini c acetylcholine receptor subtypes was examined in intracardiac neurons from the rat and guinea-pig heart by in situ hybridization techniques . Newborn guinea-pig intracardiac neurons were studied in dissociated cell culture preparations employing both S-35- and digoxigenin-labelle d oligonucleotide probes specific for the m1, m2, m3, m4 or m5 muscari nic receptor messenger RNAs. When S-35-tailed oligonucleotides were us ed, all intracardiac neurons in culture were found to express m1, m2, m3 and m4, but not m5 messenger RNAs. However after hybridization with digoxigenin-tailed probes, only m1 and m2 transcripts were detected. This may reflect differences in the sensitivity of the two techniques. Further to these experiments, intracardiac ganglia in sections of adu lt rat heart were studied employing m1-, m2-, m3- or m4-specific, S-35 -labelled oligonucleotides, and again, all intracardiac neurons expres sed messenger RNA for each of these four muscarinic receptor subtypes. Atrial myocytes in culture were only labelled by [S-35]- and digoxige nin-tailed m2 oligonucleotides. No other heart cell type seen expresse d messenger RNA for any of the muscarinic receptors. The expression of four different muscarinic receptor transcripts by intrinsic neurons o f the heart provides the molecular basis for the diverse muscarinic ac tions observed in these and other autonomic ganglia.