ATP stimulates Ca²⁺oscillations and contraction in airway smooth muscle cells of mouse lung slices

Abstract

2ϩ oscillations that were accompanied by airway contraction. After ϳ1 min, the Ca 2ϩ oscillations subsided and the airway relaxed. By contrast, Ն0.5 M adenosine 5Ј-O-(3-thiotriphosphate) (nonhydrolyzable) induced Ca 2ϩ oscillations in the SMCs and an associated airway contraction that persisted for Ͼ2 min. Adenosine 5Ј-O-(3-thiotriphosphate)-induced Ca 2ϩ oscillations occurred in the absence of external Ca 2ϩ but were abolished by the phospholipase C inhibitor U-73122 and the inositol 1,4,5-trisphosphate receptor inhibitor xestospongin. Adenosine, AMP, and ␣,␤-methylene ATP had no effect on airway caliber, and the magnitude of the contractile response induced by a variety of nucleotides could be ranked in the following order: ATP ϭ UTP Ͼ ADP. These results suggest that the SMC response to ATP is impaired by ATP hydrolysis and mediated via P2Y 2 or P2Y 4 receptors, activating phospholipase C to release Ca 2ϩ via the inositol 1,4,5-trisphosphate receptor. We conclude that ATP can serve as a spasmogen of airway SMCs and that Ca 2ϩ oscillations in SMCs are required to sustain airway contraction. calcium signaling; confocal microscopy; ATP hydrolysis ASTHMA IS AN AIRWAY DISEASE characterized by a hyperreactive response of airway smooth muscle cells (SMCs) to spasmogens such as histamine, leukotrienes, and perhaps serotonin (2, 6, 25). A major source of histamine and other agonists is an exocytotic release from inflammatory cells (i.e., mast cells and basophils) within the submucosal tissue, in close proximity to the SMCs. However, mast cell degranulation can simultaneously release another potential spasmogen, ATP, which is packaged in the same exocytotic vesicles (23). In addition, airway epithelial cells have also been identified as a source of extracellular ATP. Although the active release mechanisms of ATP from epithelial cells are not understood (5,7,11,36,37), epithelial trauma associated with asthma (12, 18) can result in damaged cells that passively release ATP.In many other tissues, ATP has been found to stimulate P2X and P2Y receptors, both of which have been identified in lung tissue (19,29,34,35 ] i ) of SMCs usually result in the phosphorylation of myosin light chain and the stimulation of contraction (15, 16), ATP is likely to be a potent spasmogen of airway SMCs.Surprisingly, the effects of ATP on the [Ca 2ϩ ] i of airway SMCs or on airway contraction have not been extensively studied, and the few reports that exist are inconsistent. For example, ATP was found to increase in vivo airway resistance in rats (9) or induce contraction in isolated guinea pig tracheae (8). On the other hand, ATP was reported to relax rabbit tracheal smooth muscle strips (1) and isolated mouse trachea (10, 17) that had been previously contracted with acetylcholine (ACh). These tissue preparations were derived from the large airways and consisted of tracheal rings or strips. As a result, these studies were not able to focus on the responses of individual SMCs. In addition, it is not clear whether results obtained from large air...

Mechanism of ACh-induced asynchronous calcium waves and tonic contraction in porcine tracheal muscle bundle

“…2-APB also produced significant inhibition of phenylephrine-induced tonic contraction of the nonpermeabilized porcine aorta, a process that is driven by IP 3 R-mediated ACW in the vascular smooth muscle (20). Furthermore, a similar concentration of xestospongin C has been shown to be effective in preventing ACh and ATP-induced ACW in the mouse bronchiolar smooth muscle cells (5,34), suggesting that xestospongin C is able to inhibit IP 3 R in the airway smooth muscle as well. The observed difference in the sensitivity to xestospongin C between ACh-induced ACW in the porcine tracheal smooth muscle and ACh-induced ACW in the mouse bronchial smooth muscle may reflect interspecies or inter-airway segment heterogeneity in the mechanism of ACW.…”

Allergic lung inflammation induces pulmonary vascular hyperresponsiveness

“…In contrast, the IP 3 -receptor antagonist xestospongin C did not influence the 5-HT-induced pressor response, although the employed concentration was three-fold above 50% of the median inhibitory concentration [45]. However, at this concentration xestospongin prevented acetylcholine-induced calcium-signalling in lung slices [46] and attenuated platelet activating factorinduced oedema formation in isolated lungs [47].…”

Novel Small Airway Bronchodilator Responses to Rosiglitazone in Mouse Lung Slices

“…To evaluate this potential, mouse lung slices were prepared containing airways with a diameter down to 50 mm, which is comparable to human airways with a diameter of 1 to 2 mm (18). This technique maintains the interdependency of the small airways with surrounding tissue and allows the visualization of airway contraction and relaxation with phasecontrast microscopy and image analysis.…”