Cellular mechanisms of acrolein-induced alteration in calcium signaling inairway smooth muscle

Acrolein, an unsaturated aliphatic aldehyde, is a potent respiratory irrita nt. We have previously observed that acrolein administered ex vivo to isola ted airways alters subsequent airway responsiveness to muscarinic agonists in terms of both mechanical activity of rings and calcium signaling in isol ated cells. In the present study, we have examined the mechanisms by which acrolein alters Ca2+ signaling. In freshly isolated rat tracheal smooth mus cle cells, preexposure to acrolein increased the [Ca2+](i) oscillation freq uency in response to endothelin 1 (ET-1, 0.1 mu M), a contractile agonist t hat acts via the activation of a receptor different from the muscarinic cho linoceptor. We then studied acrolein-induced alteration in cell signaling w ith special attention to the steps downstream of membrane receptor activati on i.e., the inositol 1,4,5-trisphosphate (InsP(3)) signaling pathway. Pret reatment of cells with LiCl (20 mM), a modulator of InsP(3) concentration, mimicked the effect of acrolein exposure on agonist-induced [Ca2+](i) respo nse, i.e., increased the amplitude of the first Ca2+ rise and the oscillati on frequency in response to 0.1 and 10 mu M acetylcholine (ACh), respective ly. Moreover, in tracheal smooth muscle, preexposure to acrolein significan tly increased carbachol-induced [H-3]inositol-phosphates accumulation, up t o 34 +/- 11% above unexposed tissue values. Finally, in beta-escin permeabi lized cells, injection of InsP(3) (0.1-10 mu M) induced a concentration-dep endent [Ca2+](i) rise followed, for high InsP(3) concentration, by [Ca2+](i ) oscillations, a calcium response whose pattern was similar to that induce d by ACh. Exposure to acrolein did not alter the InsP(3)-induced [Ca2+](i) response. These results indicate that the effect of acrolein exposure on Ca 2+ responses in airway smooth muscle is not restricted to activation of the muscarinic cholinoceptor and is due to an enhancement in agonist-induced I nsP(3) production. Since acrolein does not modify InsP(3) receptor channel sensitivity, we conclude that acrolein-induced alteration in calcium signal ing can be ascribed to its sole effect on InsP(3) production. (C) 2000 Acad emic Press.