description
One of the major tasks of the renal proximal tubule (PT) is to secrete acid into the tubule lumen, thereby reabsorbing approximately 80% of the filtered bicarbonate (HCO3(-)), as well as generating "new HCO3(-)" for regulating blood pH. In the tubular lumen, filtered HCO3(-) combines with H(+) in a reaction catalyzed by CA IV. The CO2 thus produced rapidly diffuses into the tubular cells and is combined with water to produce intracellular H(+) and HCO3(-), catalyzed by soluble cytoplasmic CA II. HCO3(-) is then cotransported with Na(+) into blood via the NBC-1. The intracellular H(+) produced by CA II is secreted into the tubular lumen predominantly via the NHE-3. The PT creates the "new HCO3(-)" by taking glutamine and metabolizing it to two molecules each of NH4(+) and HCO3(-). The NH4(+) is excreted into the tubular lumen, and the HCO3(-) , which is "new HCO3(-) ," is returned to the blood, where it replaces the HCO3(-) lost earlier in the titration of nonvolatile acids

external resources
NCBI:144182
KEGG:hsa04964
PUBMED:11826292
PUBMED:11385088
PUBMED:19721811
PUBMED:12138151
PUBMED:16914536
PUBMED:17557941
PUBMED:18056784
PUBMED:9550618
PUBMED:11045400
PUBMED:19948674
PUBMED:11533299
PUBMED:16352913

genes
AQP1 , ATP1A1 , ATP1A2 , ATP1A3 , ATP1A4 , ATP1B1 , ATP1B2 , ATP1B3 , FXYD2 , CA2 , CA4 , SLC25A10 , GLS , GLUD1 , GLUD2 , MDH1 , PCK1 , PCK2 , SLC9A3 , SLC4A4 , SLC38A3 , ATP1B4 , GLS2 ,