Differential distribution of the Sodium-vitamin C cotransporter-1 along the proximal tubule of the mouse and human kidney.

Vitamin C is reabsorbed from the renal lumen by one isoform of sodium-vitamin C co-transporters that mediate high affinity sodium-dependent L-ascorbic acid transport. Sodium-vitamin C cotransporter-1 mRNA has been detected in intestine and liver and the S3 segment of the renal proximal tubule. Here, we found that its distribution was broader and all three proximal tubule segments of mouse and human expressed the transporter but the S3 segment had the highest expression. Sodium-vitamin C co-transporter-1 expression was also found in the renal epithelial-derived LLC-PK1 cell line. Ascorbic acid transport in these cells was regulated by a single kinetic component that depended on the sodium concentration, pH and temperature. Reducing ascorbate concentration increased the apical expression of the transporter suggesting the presence of a feedback system for regulation of transporter abundance at the luminal membrane.