The effect of tumour necrosis factor-alpha (TNF alpha) on the increase in cytosolic free calcium ([Ca2+])i induced by carbachol and bradykinin (BK) was investigated in human tracheal smooth muscle cells in culture (TSMC). BK (10(-12)-10(-9) M) and carbachol (10(-7)-10(-3) M) produced a concentration-dependent increase in [Ca2+]i (pD2 = 10.73 +/- 0.05 and 5.57 +/- 0.03 respectively). The increase in [Ca2+]i was significantly enhanced for both agonists in TNF alpha-treated cells (10 ng ml-1 for 24 h). However, pD2 values were not modified (10.78 +/- 0.03 and 5.62 +/- 0.04 for BK and carbachol, respectively) suggesting that no change in the apparent receptor affinity occurred. Thus, TNF alpha induced-alterations in Ca2+ homeostasis in human TSMC may be a key mechanism underlying airway hyperreactivity.