Bradykinin elevates cytosolic Ca2+ concentration in smooth muscle cells isolated from rat duodenum

The effect of bradykinin on the cytosolic Ca2+ concentration were measured in single, Fura-2 loaded, smooth muscle cells isolated from rat duodenum. A il cells responded with a Ca2+ signal when exposed to bradykinin. The brady kinin response consisted of an initial Ca2+ spike followed by a plateau. Pr e-treatment of single muscle cells with either the phospholipase C blocker U-73122 or thapsigargin, which is a potent inhibitor of the endoplasmic ret iculum Ca2+-ATPase, inhibited the response to bradykinin. Pre-treatment of the cells with EGTA or La3+ to inhibit the Ca2+ influx, abolished the respo nse induced by bradykinin. We conclude that bradykinin applied to single sm ooth muscle cells from rat duodenum, increases cytosolic Ca2+ by emptying i ntracellular Ca2+ stores, and by contribution from extracellular Ca2+. In c ontrast to bradykinin-induced response in isolated rat duodenum (a relaxati on followed by a contraction), we did not observe a biphasic effect of brad ykinin on cytosolic Ca2+ in single muscle cells. Bradykinin may thus cause relaxation of duodenal smooth muscle indirectly through an effect on neighb ouring cells as dilatation is brought about by this agent in blood vessels.