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Effect of lipopolysaccharide on nitric oxide synthase activity in rat proximal tubules

1995; Elsevier BV; Volume: 49; Issue: 1 Linguagem: Inglês

10.1016/0006-2952(94)00449-v

1873-2968

Philip R. Mayeux, Hollye Garner, Jennifer Gibson, Victor C. Beanum,

Eicosanoids and Hypertension Pharmacology

Renal proximal tubules isolated from the rat possess nitric oxide synthase (NOS) activity that is calcium/calmodulin dependent and stereoselectively inhibited by NG-monomethyl-arginine (NMMA). In the absence of added Ca2+ and calmodulin, activity was reduced 84 ± 13% compared with the activity in the presence of 2 mM Ca2+ and 25 μg/mL calmodulin. Inhibition by EGTA (10 mM) was 95 ± 5% and by calmidazolium (R24571, 250 μM) was 99 ± 1%. Inhibition by l-NMMA (100 μM) was 78 ± 13% and by d-NMMA (100 μM) was 7 ± 7%. The majority of NOS activity was found in the soluble fraction. NOS activity in isolated proximal tubules was also examined 6 hr after a single i.v. injection of lipopolysaccharide. Activity was increased significantly (P < 0.05) in the soluble fraction by 2-fold [from 0.320 ± 0.052 to 0.648 ± 0.046 (nmol/mg protein/30 min)] and in the particulate fraction by 3-fold [from 0.081 ± 0.030 to 0.256 ± 0.034 (nmol/mg protein/30 min)]. All activities were inhibited by EGTA. These data demonstrate that proximal tubules express a calcium/calmodulin-dependent NOS activity that is increased in vivo by lipopolysaccharide.