Muscarinic signaling in ciliated tracheal epithelial cells: dual effects on Ca2+ and ciliary beating.
To examine cholinergic signal transduction pathways that modulate ciliary beat frequency (CBF), cultured ovine tracheal epithelial cells were imaged using a combination of phase-contrast (CBF) and fluorescence (Ca2+) microscopy techniques. In single cells, acetylcholine (ACh) transiently increased CBF and intracellular Ca2+ concentration ([Ca2+]i), mainly by Ca2+ release from internal stores, with a small delayed contribution from Ca2+ influx. Nicotinic agonists did not alter CBF or [Ca2+]i, whereas atropine blocked the ACh-stimulated transients, consistent with the involvement of muscarinic receptors. 4-Diphenylacetoxy-N-methylpiperidine methiodide was approximately 100 times more potent than pirenzepine in inhibiting the ACh-induced [Ca2+]i peaks, suggesting that the receptor is a pharmacologically defined (M3) subtype. Interestingly, after depletion of intracellular Ca2+ stores by thapsigargin, ACh caused a rapid transient decrease in both CBF and [Ca2+]i, again with an antagonist profile of M3 receptors. We conclude that activation of M3 muscarinic receptors initiates specific signaling pathways that act simultaneously to increase and decrease [Ca2+]i and CBF.
Salathe
M
M
Department of Molecular and Cellular Pharmacology, University of Miami School of Medicine, Florida 33136, USA.
Lipson
E J
EJ
Ivonnet
P I
PI
Bookman
R J
RJ
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002560:Cerebrovascular Circulation / Q000187:drug effects; D002923:Cilia / Q000502:physiology; D004847:Epithelial Cells; D004848:Epithelium / Q000378:metabolism / Q000502:physiology; D005110:Extracellular Space / Q000378:metabolism; D005260:Female; D007425:Intracellular Membranes / Q000378:metabolism; D009116:Muscarine / Q000378:metabolism*; D009994:Osmolar Concentration; D011950:Receptors, Cholinergic / Q000378:metabolism; D012756:Sheep; D015398:Signal Transduction; D014132:Trachea / Q000166:cytology / Q000378:metabolism / Q000502:physiology*
D011950:Receptors, Cholinergic; D009116:Muscarine; D000109:Acetylcholine; D002118:Calcium