Tumor necrosis factor-alpha augments contraction and cytosolic Ca2+ sensitivity through phospholipase A(2) in bovine tracheal smooth muscle

To elucidate the effects of tumor necrosis factor-alpha (TNF-alpha) on trac heal smooth muscle contraction, we simultaneously measured isometric tensio n and intracellular Ca2+ ([Ca2+](i)) in fura 2-loaded muscle strips. Smooth muscle force generation was evaluated in a high potassium (K+; 20.0-80.0 m M) solution and with acetylcholine (3 nM-10 mu M). TNF-alpha (1-100 ng/ml) did not directly contract muscle strips. The contractile response to acetyl choline was enhanced after application of 10 ng/ml of TNF-alpha for 30 min but not the response of [Ca2+](i). The contractile response and the respons e of [Ca2+](i) to a high K+ solution were not altered after application of TNF-alpha. The [Ca2+](i)-tension curve indicated that TNF-alpha enhanced th e responsiveness of tracheal smooth muscle through the acetylcholine-mediat ed Ca2+ sensitivity of intracellular contractile elements. The augmentation of the acetylcholine concentration-response curves for muscle tension in t he presence of TNF-alpha (10 ng/ml) was inhibited in part after application of manoalide, a phospholipase A(2) inhibitor. We conclude that a low conce ntration of TNF-alpha enhances smooth muscle responsiveness to acetylcholin e by agonist-mediated Ca2+ sensitivity facilitated by phospholipase A(2). ( C) 2000 Elsevier Science B.V. All rights reserved.