Variability in pK'1 of human plasma

Area of Science:

• Biochemistry
• Physiological Chemistry

Background:

• Understanding the behavior of carbonic acid in plasma is crucial for acid-base balance.
• The apparent first dissociation constant of carbonic acid (pK'1) is a key parameter in physiological pH calculations.
• Ionic strength is a known factor influencing chemical equilibria, but its specific effect on plasma pK'1 requires detailed investigation.

Purpose of the Study:

• To investigate the relationship between ionic strength and pK'1 in human plasma.
• To determine how variations in ionic strength and bicarbonate concentration affect pK'1.
• To assess the impact of pK'1 changes on measured plasma pH.

Main Methods:

• Human plasma samples from healthy individuals were used.
• Ionic strength was manipulated by adding NaCl and NaHCO3.
• pK'1 was determined by measuring pH, PCO2, and TCO2 at 37°C under controlled gas mixtures.

Main Results:

• Significant variability in pK'1 was observed in fresh, undiluted plasma and extrapolated values at zero ionic strength.
• Plasma ionic strength was found to alter pK'1.
• Changes in plasma bicarbonate concentration also affected pK'1, consequently altering measured pH.

Conclusions:

• Ionic strength is a critical determinant of pK'1 in human plasma.
• Variations in ionic strength and bicarbonate levels have a direct impact on plasma acid-base status.
• These findings highlight the importance of considering ionic strength in accurate physiological pH measurements.