Intracellular pH in cold-blooded vertebrates as a function of body temperature.
Intracellular pH (pHi) was measured in vivo in tissue of frogs (Rana catesbeiana) and turtles (Pseudemys scripta) using the DMO technique. Animals were permitted 3-8 days to come to a new steady-state body temperature (Tb) which ranged 5-32 degrees C. Least squares regression equation for pHi data are: frog blood, 8.184-0.0206 Tb; frog striated muscle, 7.275-0.0152 Tb; turtle blood, 8.092-0.0207Tb; turtle muscle, 7.421-0.0186 Tb; turtle heart, 7.452-0.0122 Tb; turtle liver, 7.753-0.0233 Tb; turtle esophageal smooth muscle, 7.513-0.0141 Tb. Only turtle cardiac muscle deltapHi/deltaT was significantly different from deltapH/deltaT of blood. Results have been interpreted in terms of protein charge state alterations; in the physiological pH range, histidine residues of proteins are the principal dissociable groups (HPr+ = H+ + Pr) affected by pHi and Tb changes. Constancy of protein charge state can be assessed by monitoring alpha imidazole, alphaIM = Pr/(HPr+ + Pr). A uniform pKIM of 6.85 (20degreesC) and a deltaHO of 7 kcal/mol are assumed in calculating alphaIM. Intracellular alphaIM is preserved in the tissues studied as body temperature changes. These results indicate that ectotherm acid-base balance, alphastat control, regulates not only extracellular blood proteins, but also intracellular compartment proteins in such a way as to preserve functions dependent upon protein net charge states.
D000136:Acid-Base Equilibrium; D000818:Animals; D001826:Body Fluids / Q000378:metabolism*; D001831:Body Temperature; D001834:Body Water / Q000378:metabolism; D002245:Carbon Dioxide / Q000097:blood; D004947:Esophagus / Q000378:metabolism; D005110:Extracellular Space / Q000378:metabolism; D006352:Heart Ventricles / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007424:Intracellular Fluid / Q000378:metabolism*; D008099:Liver / Q000378:metabolism; D009130:Muscle, Smooth / Q000378:metabolism; D009132:Muscles / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D011892:Rana catesbeiana / Q000378:metabolism; D014426:Turtles / Q000378:metabolism
D011506:Proteins; D002245:Carbon Dioxide