AJP - Lung Cellular and Molecular Physiology, Vol 269, Issue 2 234-L240, Copyright © 1995 by American Physiological Society
Serotonin-evoked calcium transients in airway smooth muscle cells
B. Tolloczko, Y. L. Jia and J. G. Martin
Seymour Heisler Laboratory, Montreal Chest Hospital Research Center, Quebec, Canada.
Serotonin (5-HT) is an important mediator of allergic airway narrowing in
several animal species. The present study was designed to characterize the
receptor subtypes that mediate 5-HT-induced airway responses in the rat. To
do this, we measured Ca2+ transients and adenosine 3',5'-cyclic
monophosphate (cAMP) production evoked by 5-HT in cultured rat tracheal
smooth muscle cells as well as 5-HT-induced contractions of isolated
tracheal rings. 5-HT (10(-6) to 10(-4) M) triggered a rapid increase in
intracellular Ca2+ concentration ([Ca2+]i) followed by a second phase of
sustained, elevated, and sometimes oscillating levels of [Ca2+]i. Sustained
but not peak [Ca2+]i levels were dependent on Ca2+ influx but were not
attenuated by nifedipine (10(-5) M). Oscillations were observed in cells in
Ca2+ -free medium, suggesting Ca2+ -induced Ca2+ release independent of
Ca2+ influx. The effects of 5-HT were inhibited by thapsigargin (10(-6) M)
and ketanserin (10(-7) M). In cells incubated with LY-278,584 (5-HT3
antagonist) and (-)pindolol (5-HT1 antagonist), 5-HT-evoked responses were
not significantly different from the control values. 5-methyltryptamine
(5-MT), a ligand with higher affinity for 5-HT2C receptors than "classical"
5-HT2 receptors, elicited higher responses than
dipropyl-5-carboxamidotryptamine (DP-5-CT), which possesses lower affinity
for 5-HT2C receptors than 5-MT, but an affinity for the classical 5-HT2
receptor similar to 5-MT, but an affinity for the classical 5-HT2 receptor
similar to 5-MT.(ABSTRACT TRUNCATED AT 250 WORDS)
