INHIBITION OF ECTO-5'-NUCLEOTIDASE BY NITRIC-OXIDE DONORS - IMPLICATIONS IN RENAL EPITHELIAL-CELLS

We evaluated, in renal epithelial cells with a proximal tubule phenoty pe, the effect of nitric oxide (NO) on ecto-5'-nucleotidase (5'-NU), t he underlying mechanism and its functional consequence. Sodium nitropr usside (SNP, 1-1000 mu M), a NO donor, inhibited 5'-NU activity in a t ime- and concentration-dependent manner. Consequently, NO blunted the inhibition by extracellular cyclic AMP (cAMP, 10-1000 mu M) of sodium- phosphate co-transport, a pathway which involves degradation of adenos ine monophosphate (AMP) by 5'-NU. SNP-induced inhibition of 5'-NU was not mediated by cyclic GMP, since it was not mimicked by atrial natriu retic peptide, and was reproduced by isosorbide dinitrate and sodium n itrate, two NO donors. SNP and genuine NO decreased the activity of 5' -NU in renal homogenates, and the effect of SNP was potentiated by dit hiothreitol and glutathione, but not by nicotinamide adenine dinucleot ide. In vivo in rats, kidney ischemia/reperfusion, which activates ind ucible NO-synthase, inhibited renal 5'-NU. This inhibition was prevent ed by N omega-nitro-L-arginine methyl ester, a NO-synthase inhibitor. These results indicate that: (i) NO-related activity inhibited the act ivity of an ecto-enzyme, 5'-NU, most likely through S-nitrosylation of the enzyme; (ii) inhibition of 5'-NU activity by NOx, which can occur in vivo under pathophysiological conditions, affected the extent to w hich extracellular cAMP inhibited sodium-P-i cotransport.