Premium
Weak acid‐concentration A tot and dissociation constant K a of plasma proteins in racehorses
Author(s) -
STäMPFLI H. R.,
MISIASZEK S.,
LUMSDEN J. H.,
CARLSON G. P.,
HEIGENHAUSER G. J. F.
Publication year - 1999
Publication title -
equine veterinary journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.82
H-Index - 87
eISSN - 2042-3306
pISSN - 0425-1644
DOI - 10.1111/j.2042-3306.1999.tb05262.x
Subject(s) - chemistry , titration , dissociation (chemistry) , dissociation constant , horse , plasma , ion , analytical chemistry (journal) , titration curve , electrolyte , chromatography , biochemistry , inorganic chemistry , paleontology , physics , receptor , organic chemistry , quantum mechanics , biology , electrode
Summary The plasma proteins are a significant contributor to the total weak acid concentration as a net anionic charge. Due to potential species difference, species‐specific values must be confirmed for the weak acid anionic concentrations of proteins (A tot ) and the effective dissociation constant for plasma weak acids (K a ). We studied the net anion load A tot of equine plasma protein in 10 clinically healthy mature Standardbred horses. A multi‐step titration procedure, using a tonometer covering a titration range of PCO 2 from 25 to 145 mmHg at 37° C , was applied on the plasma of these 10 horses. Blood gases (pH, PCO 2 ) and electrolytes required to calculate the strong ion difference ([SID] = [(Na + +K + +Ca 2+ +Mg 2+ )‐(Cl − +Lac+PO 4 2‐ )]) were simultaneously measured over a physiological pH range from 6.90–7.55. A nonlinear regression iteration to determine A tot and K a was performed using polygonal regression curve fitting applied to the electrical neutrality equation of the physico‐chemical system. The average anion‐load A tot for plasma protein of 10 Standardbred horses was 14.89 ± 0.8 mEq/l plasma and K a was 2.11 ± 0.50 × 10 −7 Eq/l (pK a = 6.67). The derived conversion factor (iterated A tot concentration/average plasma protein concentration) for calculation of A tot in plasma is 0.21 mEq/g protein (protein‐unit: g/l). This value compares closely with the 0.24 mEq/g protein determined by titration of Van Slyke et al. (1928) and 0.22 mEq/g protein recently published by Constable (1997) for horse plasma. The Ka value compares closely with the value experimentally determined by Constable in 1997 (2.22 × 10 7 Eq/l). Linear regression of a set of experimental data from 5 Thoroughbred horses on a treadmill exercise test, showed excellent correlation with the regression lines not different from identity for the calculated and measured variables pH, HCO 3 and SID. Knowledge of A tot and K a for the horse is useful especially in exercise studies and in clinical conditions to quantify the mechanisms of the acid‐base disturbances occurring.