Acetylcholine-induced contraction in human isolated bronchial smooth muscle: role of an intracellular calcium store.

The aim of this study was to investigate the role played by an intracellular calcium store in human bronchoconstriction. Human isolated bronchial smooth muscle strips (5-6 mm long, 0.4-0.5 mm wide) were taken from lung specimens during pneumonectomy. Isometric contraction was recorded after stimulation by 10(-4) M acetylcholine in physiological solutions. The amplitude of acetylcholine-induced contractions was measured in the presence and absence of calcium ions in the perfusing medium. When the perfusing medium was switched to a calcium-free solution the amplitude of the acetylcholine-induced contraction was measured with respect to the duration of calcium-free perfusion. The amplitude of the contraction was 82.1 +/- 11.3%, 77.2 +/- 15.4%, 63 +/- 10.6% of the maximum contraction after the strips were perfused in calcium-free solutions for 1, 3 and 5 min respectively. Several successive contractions could be elicited, and even after 20 min of calcium-free perfusion, acetylcholine was still able to elicit contractions. These results suggest that an intracellular calcium store may be involved in human bronchoconstriction. This finding may help further our understanding of the effects of calcium antagonists on human airways.