Muscarinic receptors in human airway smooth muscle are coupled to phosphoinositide metabolism.

In the present study we investigated whether muscarinic receptors in human airway smooth muscle are coupled to phosphoinositide metabolism as a possible transduction mechanism of contraction. Using isolated bronchial smooth muscle preparations, we found that the muscarinic agonist methacholine caused a time- and concentration-dependent accumulation of inositol phosphates in the presence of lithium, an effect which could be inhibited by atropine. Apart from its physiological significance, this finding may have great relevance for the biochemical investigation of cholinergic hyperresponsiveness in the airways of asthmatic patients.