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.


CONCLUSIONS
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.
Markovich
D
D
Department of Physiology and Pharmacology, University of Queensland, Australia; Institute of Physiology, University of Zurich, Zurich, Switzerland. danielm@plpk.uq.edu.au
Wang
H
H
Puttaparthi
K
K
Zajicek
H
H
Rogers
T
T
Murer
H
H
Biber
J
J
Levi
M
M
D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D027682:Cation Transport Proteins; D005260:Female; D015870:Gene Expression; D066298:In Vitro Techniques; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D008297:Male; D008845:Microinjections; D008871:Microvilli / Q000378:metabolism; D009865:Oocytes / Q000378:metabolism; D011191:Potassium Deficiency / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000008:administration & dosage / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000378:metabolism*; D000077003:Sodium Sulfate Cotransporter; D013431:Sulfates / Q000097:blood / Q000378:metabolism* / Q000652:urine; D027981:Symporters; D014982:Xenopus laevis
D002352:Carrier Proteins; D027682:Cation Transport Proteins; D012333:RNA, Messenger; D000077003:Sodium Sulfate Cotransporter; D013431:Sulfates; D027981:Symporters; D012964:Sodium