NO-induced modulation of calcium-oscillations in pulmonary vascular smoothmuscle

The effect of the nitric oxide (NO) donor sodium nitroprusside (SNP) on bot h [Ca2+](i) and mechanical activity was studied in the rat isolated pulmona ry artery (RPA). In freshly isolated myocytes loaded with 1 mu M indo-lace- toxymethyl ester for 30 min, short (40-60 s) application of ATP (100 mu M) or ET-1 (0.1 mu M) induced 3-6 cyclic rises in [Ca2+](i) (Ca-oscillations) of decreasing amplitude. Preincubation of cells with SNP (10-250 mu M) for 10 min had no effect on the resting [Ca2+](i) value, but progressively abol ished the oscillations. A similar effect was obtained with 8-bromo-cGMP (10 0-500 mu M). SNP (0.001-100 mu M) concentration-dependently relaxed ATP (10 mM, n = 4) and ET-1 (0.1 mu M, n = 4)-precontracted RPA. 1H-[1,2,4]oxadiaz olol [4,3,-a]quinoxalin-1-one (ODQ, 10 mu M), a potent inhibitor of the cyt osolic guanylyl cyclase, fully reversed the effect of SNP on ATP-induced [C a2+](i) oscillations as well as on ATP-precontracted RPA. In contrast, N-[2 -(methylamino)ethyl]-5-isoquinolinesulfonamide (H8, 10 mu M), a potent inhi bitor of cGMP-dependent protein kinase (PKG), did not alter the effect of S NP Caffeine (5 mM) induced only one transient [Ca2+](i)-increase (n = 24), the amplitude of which was altered neither by SNP nor by 8-bromo-cGMP. Our results show that the relaxing effect of NO in RPA is related, at least in part, to its action on the Ca-signalling pathway. NO interacts with inosito l trisphosphate pathway without interacting with the ryanodine-sensitive re ceptor. Finally, the effect of NO involves an increase in cGMP but appears independent of activation of PKG. (C) 2000 Harcourt Publishers Ltd.