Sodium Loading Changes Urinary Protein Excretion: a Proteomic Analysis

Plasma sodium concentration is maintained even when sodium intake is altered. Sodium homeostasis may involve changes in renal tubular protein expression that are reflected in the urine. We used proteomic analysis to investigate changes in urinary protein excretion in response to acute sodium loading. Rats were given deionized water followed by hypertonic (2.7%) saline for 28 h each. Urinary protein expression was determined during the final 4 h of each treatment. Acute sodium loading increased urinary sodium excretion (4.53 +/- 1.74 vs. 1.70 +/- 0.27 mmol/day, P = 0.029). Urinary proteins were separated by two-dimensional PAGE and visualized by Sypro ruby staining. Differentially expressed proteins were identified by matrix-assisted laser desorption ionization-time-of-flight mass spectrometry followed by peptide mass fingerprinting. The abundance of a total of 45 protein components was changed after acute sodium loading. Neutral endopeptidase, solute carrier family 3, meprin 1alpha, diphor-1, chaperone heat shock protein 72, vacuolar H(+)-ATPase, ezrin, ezrin/radixin/moesin-binding protein, glutamine synthetase, guanine nucleotide-binding protein, Rho GDI-1, and chloride intracellular channel protein 1 were decreased, whereas albumin and alpha-2u globulin were increased. Some of these proteins have previously been shown to be associated with tubular transport. These data indicate that alterations in the excretion of several urinary proteins occur during acute sodium loading.