MUSCARINIC SIGNALING IN CILIATED TRACHEAL EPITHELIAL-CELLS - DUAL EFFECTS ON CA2+ AND CILIARY BEATING

To examine cholinergic signal transduction pathways that modulate cili ary beat frequency (CBF), cultured ovine tracheal epithelial cells wer e imaged using a combination of phase-contrast (CBF) and fluorescence (Ca2+) microscopy techniques. In single cells, acetylcholine (ACh) tra nsiently increased CBF and intracellular Ca2+ concentration ([Ca2+](i) ), mainly by Ca2+ release from internal stores, with a small delayed c ontribution from Ca2+ influx. Nicotinic agonists did not alter CBF or [Ca2+](i), whereas atropine blocked the ACh-stimulated transients, con sistent with the involvement of muscarinic receptors. 4-Diphenylacetox y-N-methylpiperidine methiodide was similar to 100 times more potent t han pirenzepine in inhibiting the ACh-induced [Ca2+](i) peaks, suggest ing that the receptor is a pharmacologically defined (Ms) subtype. Int erestingly, after depletion of intracellular Ca2+ stores by thapsigarg in, ACh caused a rapid transient decrease in both CBF and [Ca2+](i), a gain with an antagonist profile of M(3) receptors. We conclude that ac tivation of Ms muscarinic receptors initiates specific signaling pathw ays that act simultaneously to increase and decrease [Ca2+](i) and CBF .