VIRUS-INDUCED AND INTERFERON-INDUCED LOSS OF INHIBITORY M-2 MUSCARINIC RECEPTOR FUNCTION AND GENE-EXPRESSION IN CULTURED AIRWAY PARASYMPATHETIC NEURONS

Viral infections increase vagally mediated reflex bronchoconstriction. Decreased function of inhibitory M-2 muscarinic receptors on the para sympathetic nerve endings is likely to contribute to increased acetylc holine release. In this study, we used cultured airway parasympathetic neurons to determine the effects of parainfluenza virus and of interf eron (IFN)-gamma on acetylcholine release, inhibitory M-2 receptor fun ction, and M-2 receptor gene expression, In control cultures, electric ally stimulated acetylcholine release increased when the inhibitory M- 2 receptors were blocked using atropine (10(-5) M) and decreased when these receptors were stimulated using methacholine (10(-5) M). Acetylc holine release was increased by viral infection and by treatment with IFN-gamma (300 U/mol). In these cells, atropine did not further potent iate, nor did methacholine inhibit, acetylcholine release, suggesting decreased inhibitory M-2 receptor function and/or expression. Using a competitive reverse transcription-polymerase chain reaction method, we demonstrated that M-2 receptor gene expression was decreased by more that an order of magnitude both by virus infection and by treatment wi th IFN. Thus, viral infections may increase vagally mediated bronchoco nstriction both by directly inhibiting M-2 receptor gene expression an d by causing release of IFN-gamma which inhibits Mt receptor gene expr ession.