Acid-base transport by the renal proximal tubule.
One of the major tasks of the renal proximal tubule is to secrete acid into the tubule lumen, thereby reabsorbing approximately 80% of the filtered HCO3- as well as generating new HCO3- for regulating blood pH. This review summarizes the cellular and molecular events that underlie four major processes in HCO3- reabsorption. The first is CO2 entry across the apical membrane, which in large part occurs via a gas channel (aquaporin 1) and acidifies the cell. The second process is apical H+ secretion via Na-H exchange and H+ pumping, processes that can be studied using the NH4+ prepulse technique. The third process is the basolateral exit of HCO3- via the electrogenic Na/HCO3 co-transporter, which is the subject of at least 10 mutations that cause severe proximal renal tubule acidosis in humans. The final process is the regulation of overall HCO3- reabsorption by CO2 and HCO3- sensors at the basolateral membrane. Together, these processes ensure that the proximal tubule responds appropriately to acute acid-base disturbances and thereby contributes to the regulation of blood pH.
Boron
Walter F
WF
Department of Cellular and Molecular Physiology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520-8026, USA. walter.boron@yale.edu
D000136:Acid-Base Equilibrium / Q000502:physiology*; D000641:Ammonia / Q000378:metabolism; D000804:Angiotensin II / Q000502:physiology; D000818:Animals; D051398:Aquaporin 1 / Q000502:physiology; D001639:Bicarbonates / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism; D006801:Humans; D007687:Kidney Tubules, Proximal / Q000502:physiology*; D011505:Protein-Tyrosine Kinases / Q000502:physiology; D027982:Sodium-Bicarbonate Symporters / Q000235:genetics / Q000502:physiology
D001639:Bicarbonates; C498898:SLC4A4 protein, human; D027982:Sodium-Bicarbonate Symporters; D000804:Angiotensin II; D002245:Carbon Dioxide; D051398:Aquaporin 1; D000641:Ammonia; D011505:Protein-Tyrosine Kinases