The association between calcium and acetoacetate, 3-hydroxybutyrate, pyruvate and lactate as determined by potentiometry

Abstract

The complex binding of calcium to acetoacetate, 3-hydroxybutyrate, lactate and pyruvate was studied under physiological temperature and ionic strength by Potentiometrie measurement of the calcium ion activity. The limiting conductances of the complex-forming anions were measured to make a proper correction for the analytical error due to the liquid junction potential between the test solution and the salt bridge solution of the reference electrode. The calcium activity measurements indicate a 1:1 binding ratio of calcium and the anions. The concentrational complexity constants at physiological ionic strength of calcium and acetoacetate, 3-hydroxybutyrate, lactate and pyruvate are 8.8, 4.0,11.6 and 6.31/mol, respectively, and the limiting conductances of the anions are 4.5, 3.8, and 5.2×10^-3 S·m²/mol, respectively. The thermodynamical complexity constants, which are based on ion activities, are about three times higher than the concentrational complexity constants.

The possible role of the various complexes in lactic acidosis and ketoacidosis is discussed, and it is concluded that under merely moderate lactic acidosis the quantitatively most important of the low-molecular weight calcium complexes is the calcium-lactate complex.

Key words:

• activity coefficients
• calcium-bicarbonate complex
• Debye-Hückel equation
• lactate/pyruvate ratio