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.
Division of Environmental and Evolutionary Biology, University of Glasgow, Scotland. kgilmour@udcf.gla.ac.uk
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Gilmour
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