Claudins are a family of tight junction proteins that provide size and charge selectivity to solutes traversing this route. Claudin function can be regulated by posttranslational modifications that affect their localization. Claudin-19 is expressed in TALs and has been implicated in the regulation of Na permeability in this segment. We previously showed that nitric oxide (NO) via cGMP decreases paracellular Na reabsorption in TALs, but the mechanism by which this occurs has not been elucidated. We hypothesize that NO/cGMP regulate claudin-19 trafficking to the plasma membrane. To test this we measured the effects of a NO donor or cGMP on dilution potentials in perfused isolated TALs from Sprague Dawley rats with and without antibodies against an extracellular domain of claudin-19 and Tamm-Horsfall protein (control). Dilution potentials were generated by reducing bath NaCl from 141 to 32 mM. During the control period, the dilution potential was -18.2 ± 1.8 mV. After the NO donor spermine NONOate (SPM; 200 μM) was added, it fell to -14.7 ± 2 mV (n = 8; p < 0.04). In the presence of the claudin-19 antibody, SPM had no significant effect on dilution potentials (claudin-19 antibody alone: -12.7 ± 2.1 mV vs claudin-19 antibody + SPM: -12.9 ± 2.4 mV; n = 6). The claudin-19 antibody alone had no effect on dilution potentials. In the presence of the Tamm-Horsfall protein antibody, SPM reduced the dilution potential from -9.7 ± 1.0 mV to -6.3 ± 1.1 mV (p<0.006, n = 6). Dibutyryl cGMP (500 uM) reduced the dilution potential -19.6 ± 2.6 mV to -17.2 ± 2.3 mV (n = 6; p < 0.02). Dibutyryl-cGMP increased surface expression of claudin-19 from 29.9 ± 3.8% to 65.9 ± 10.1 % (n = 6; p < 0.02) while reducing total expression from 13.3 ± 1.9 to 9.5 ± 1.5 arbitrary units (p< 0.003). We conclude that NO via cGMP reduces Na reabsorption via the paracellular pathway by increasing the amount of claudin-19 in the plasma membrane. We speculate that NO increases both insertion of claudin-19 into and retrieval from the plasma membrane, and the latter leads to enhanced degradation.