Abstract
Low Na+ intake activates aldosterone signaling, which increases renal Na+ reabsorption through increased apical activity of the NaCl cotransporter (NCC) and the epithelial Na+ channel (ENaC). Na+ transporter proteins are excreted in urine as an integral part of cell-derived extracellular vesicles (uEVs). It was hypothesized that Na+ transport protein levels in uEVs from healthy humans reflect their physiological regulation by aldosterone. Urine and plasma samples from 10 healthy men (median age: 22.8 yr) were collected after 5 days on a low-Na+ (70 mmol/day) diet and 5 days on a high-Na+ (250 mmol/day) diet. uEVs were isolated by ultracentrifugation and analyzed by Western blot analysis for EV markers (CD9, CD63, and ALIX), transport proteins (Na+-K+-ATPase α1-subunit, NCC, ENaC α- and γ-subunits, and aquaporin 2), and the ENaC-cleaving protease prostasin. Plasma renin and aldosterone concentrations increased during the low-Na+ diet. uEV size and concentration were not different between diets by tunable resistive pulse sensing. EV markers ALIX and CD9 increased with the low-Na+ diet, whereas CD63 and aquaporin 2 excretion were unchanged. Full-length ENaC γ-subunits were generally not detectable in uEVs, whereas ENaC α-subunits, NCC, and phosphorylated NCC were consistently detected but not changed by Na+ intake. Prostasin increased with low Na+ in uEVs. uEV excretion of transporters was not correlated with blood pressure, urinary Na+ and K+ excretion, plasma renin, or aldosterone. In conclusion, apical Na+ transporter proteins and proteases were excreted in uEVs, and while the excretion rate and size of uEVs were not affected, EV markers and prostasin increased in response to the low-Na+ diet.