The buffer capacity and buffer systems of human whole saliva measured without loss of CO2

The buffer capacity of unstimulated (UWS) and stimulated (SWS) whole-mouth saliva involves three major buffer systems. The aim was to determine the bu ffer capacity of UWS and SWS at specific pH in the interval from pH 7.5 dow n to pH 3.0. The contribution of each of the buffer systems was also determ ined under conditions resembling those in the mouth. UWS and SWS were colle cted from 20 healthy volunteers; the saliva was collected under paraffin oi l in order to avoid loss of CO2. The buffer capacity of UWS and SWS in samp les with and without bicarbonate (HCO3-) and CO2 were measured at various p H by acid titration in a closed system at 36 degrees C. The mean concentrat ions of the buffer systems in UWS (mean flow rate 0.55 ml/min) were 4.4 mmo l/l HCO3-, 4.5 mmol/l phosphate (of which 1.3 mmol/l was present in the for m of HPO42-), 1876 mu g/ml protein; the saliva pH was 6.8 and the P-CO2 29. 3 mmHg. The corresponding mean concentrations in SWS (mean how rate 1.66 ml /min) were 9.7 mmol/l HCO3-, 3.8 mmol/l phosphate (of which 1.9 mmol/l was present in the form of HPO42-), 1955 mu g/ml protein; pH 7.2 and P-CO2 25.7 mmHg. The highest buffer capacity of UWS and SWS was 6.0 and 8.5 mmol H+/( 1 saliva*pH unit) at pH 6.25, respectively. At saliva pH in the range from pH 7 down to pH 5, the following had significant impact on buffer capacity: the HCO3- concentration (p < 0.001), the flow rate (p < 0.01), and the pH of the saliva (p < 0.05). At acidic pH in the range from pH 5 down to pH 4, however, only the protein concentration had a significant impact on buffer capacity (p < 0.01). (C) 2000 Elsevier Science Ltd. All rights reserved.