Nitric oxide enhances paracellular permeability of opossum kidney cells

Background. Nitric oxide (NO) has been shown to be a paracrine/autocrine regulator of proximal tubular transport. In this study, we investigated the effect of NO on the paracellular permeability of opossum kidney (OK) cells, a proximal tubule cell line that possesses a leaky paracellular pathway resembling that of the in vivo proximal tubule. Methods. Paracellular permeability of OK cells cultured on permeable supports was measured as the apparent paracellular permeability coefficient (P-app) for (3)[H]-D-mannitol. Changes in cell viability, cellular adenosine triphosphate (ATP) content, cGMP levels, and lipid peroxidation were assessed. Results. Incubation with 2 mM sodium nitroprusside (SNP), an NO donor, for 24 hours significantly enhanced the P-app of OK cell sheets by 30.6+/-7.0% (N = 8, P < 0.05). This effect was largely blunted by hemoglobin, a NO scavenger. Cell viability was not compromised. This effect of SNP was concomitant with a moderate reduction of cellular ATP content, an increase in lipid peroxidation, and an increase in cellular cGMP levels. The antioxidant superoxide dismutase (SOD) significantly attenuated the effect of SNP on cellular ATP content and blunted the increase in P-app caused by SNP. A soluble guanylate cyclase inhibitor did not affect the effect of SNP on the P-app. Conclusions. NO enhances the paracellular permeability of OK cells possibly via mechanisms involving decreases in cellular ATP content.