The disequilibrium pH: a tool for the localization of carbonic anhydrase.
The disequilibrium pH is defined as any discrepancy between the measured pH and the pH which would exist if CO2-HCO3-H+ reactions were at equilibrium. Measurement of the disequilibrium pH can be used to assess the status of CO2-HCO3--H+ reactions and, in combination with carbonic anhydrase (CA) or CA inhibitor treatments, may also be used to localize CA. Renal physiologists have used disequilibrium experiments to determine that HCO3- reabsorption in the kidney tubule occurs via proton secretion, and that CA activity is available to ultrafiltrate CO2-HCO3-H+ reactions in the proximal convoluted tubule, but not the distal tubule. Disequilibrium experiments were also used in investigating the availability of CA to CO2-HCO3--H+ reactions in water at the fish gill; the opposing results obtained in two studies have not yet been resolved. Respiratory physiologists have used the disequilibrium technique in vivo and with saline-perfused preparations to assess the availability of CA to plasma CO2-HCO3--H+ reactions following gas exchange. Saline-perfused preparations enable direct localization of CA activity, while in vivo measurements encompass the numerous factors affecting CO2-HCO3--H+ equilibration in a multi-phase solution. Given the many organs in which membrane-bound CA activity has now been identified, the usefulness of the disequilibrium pH technique has increased beyond its original applications in renal and pulmonary physiology.
Gilmour
K M
KM
Division of Environmental and Evolutionary Biology, University of Glasgow, Scotland. kgilmour@udcf.gla.ac.uk
D000136:Acid-Base Equilibrium; D000143:Acids / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000502:physiology; D002256:Carbonic Anhydrases / Q000378:metabolism*; D005399:Fishes / Q000378:metabolism; D005740:Gases / Q000097:blood / Q000378:metabolism; D005880:Gills / Q000378:metabolism; D006859:Hydrogen / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007668:Kidney / Q000378:metabolism; D014018:Tissue Distribution; D014867:Water / Q000378:metabolism
D000143:Acids; D005740:Gases; D014867:Water; D006859:Hydrogen; D002256:Carbonic Anhydrases; D002118:Calcium