Angiotensin II-induced Ca2+-oscillations in vascular myocytes from the rat pulmonary artery

The effect of angiotensin II (ANG II) on the cytosolic calcium concentration ([Ca2+](i)) was studied in freshly (2-8 h) isolated myocytes from the main pulmonary artery of the rat. Myocytes were loaded with the fluorescent indicator indo 1 (1 mu M for 30 min) and experiments were performed at room temperature. Short (30 s) applications of ANG II (0.01-10 mu M) induced cyclic variations (oscillations) in [Ca2+](i). The ANG II-induced response was typically composed of three to six oscillations of constant duration (9.8 +/- 0.5 s, n = 40) but of decreasing amplitude. The first oscillation increased [Ca2+](i) from 119 +/- 4 to 884 +/- 33 nM (n = 32). ANG II-induced response was concentration dependently inhibited by previous addition to the bathing solution of losartan or SR-47436 (0.01-0.1 mu M, each), two specific AT(1) receptor-antagonists. In Ca2+-free external solutions (containing 0.4-1 mM EGTA), ANG II still produced oscillation in [Ca2+](i). These oscillations disappeared in myocytes pretreated with neomycin (0.1 mu M), thapsigargin (1 mu M), or phorbol 12,13-dibutyrate (PDBu, 1 mu M). In contrast to ANG II, caffeine (0.5-10 mM) induced only one transient rise in [Ca2+](i), which was unaltered by neomycin or PDBu but blocked by thapsigargin. These results show that ANG II produces oscillations in [Ca2+]i in pulmonary arterial myocytes via stimulation of AT(1) receptors coupled to phospholipase C activation. ANG II-induced oscillations appear to be related to the cycling of Ca2+ ions from an intracellular store (presumably the sarcoplasmic reticulum) by a primarily inositol trisphosphate-dependent Ca2+ release.