Chronic K depletion inhibits renal brush border membrane Na/sulfate cotransport.

Chronic K depletion inhibits renal brush border membrane Na/sulfate cotransport. Background. The purpose of this study was to determine if dietary potassium (K) deficiency regulates renal proximal tubular sodium gradient-dependent sulfate transport (Na/Si cotransport) in the rat and, furthermore, determine if the regulation takes place at the level of the recently cloned Na/Si cotransport system (NaSi -1). Methods and Results. Rats treated chronically (seven days) with a K-deficient diet had a significant decrease in serum Si levels and an increase in fractional excretion of ultrafilterable Si , which paralleled a significant decrease in brush border membrane (BBM) Na/Si cotransport activity. The decrease in BBM Na/Si cotransport activity was associated with decreases in BBM NaSi -1 protein and renal cortical NaSi -1 mRNA abundance. In addition, in Xenopus oocytes injected with mRNA from kidney cortex slices of K-deficient rats, there was a significant reduction in the induced Na/Si cotransport, whereas there was no alteration in l-leucine uptake, suggesting that in K-deficient rats, there is a specific decrease in functional mRNA encoding the NaSi -1 mRNA. Conclusion. These findings indicate that chronic K deficiency leads to a reduction in serum Si levels and an increase fractional excretion of Si , and reduces Si reabsorption by down-regulating the expression of the proximal tubular Na/Si -1 cotransporter protein and mRNA. [ABSTRACT FROM AUTHOR]