Arachidonic acid induces [Ca2+]i oscillations in smooth muscle cells from human airways

The role of phospholipase A2 (PLA2) in mediating agonist-stimulation of bronchial contraction has not yet been studied at a cellular level. The aim of the present work was to examine the Ca2+ signal elicited in human bronchial smooth muscle cells by exogenous arachidonic acid (AA), a first product of PLA2 activity. To study the effect of AA (2-20 microM) on [Ca2+]i, a single cell video imaging technique was used. AA induced various patterns of [Ca2+]i increase; most frequently, [Ca2+]i oscillations were observed. The amplitude of [Ca2+]i repetitive peaks, but not the frequency, was dependent on AA concentration. In the absence of external Ca2+, AA evoked a slower and reduced transient increase in [Ca2+]i. It is concluded that AA or some of its metabolites release Ca2+ from intracellular stores and that a contribution of extracellular Ca2+ is essential for [Ca2+]i oscillations.