Tumor necrosis factor-α augments contraction and cytosolic Ca 2+ sensitivity through phospholipase A 2 in bovine tracheal smooth muscle

Abstract

To elucidate the effects of tumor necrosis factor-α (TNF-α) on tracheal smooth muscle contraction, we simultaneously measured isometric tension and intracellular Ca 2+ ([Ca 2+] i) in fura 2-loaded muscle strips. Smooth muscle force generation was evaluated in a high potassium (K +; 20.0–80.0 mM) solution and with acetylcholine (3 nM–10 μM ). TNF-α (1–100 ng/ml) did not directly contract muscle strips. The contractile response to acetylcholine was enhanced after application of 10 ng/ml of TNF-α for 30 min but not the response of [Ca 2+] i. The contractile response and the response of [Ca 2+] i to a high K + solution were not altered after application of TNF-α. The [Ca 2+] i–tension curve indicated that TNF-α enhanced the responsiveness of tracheal smooth muscle through the acetylcholine-mediated Ca 2+ sensitivity of intracellular contractile elements. The augmentation of the acetylcholine concentration–response curves for muscle tension in the presence of TNF-α (10 ng/ml) was inhibited in part after application of manoalide, a phospholipase A 2 inhibitor. We conclude that a low concentration of TNF-α enhances smooth muscle responsiveness to acetylcholine by agonist-mediated Ca 2+ sensitivity facilitated by phospholipase A 2.