Salivary viscosity and lubrication: influence of pH and calcium

The viscosity of human whole saliva and six salivary protein fractions was studied at different pH levels in the presence and absence of calcium. Changes in pH significantly influenced the viscosity of whole saliva, and centrifugation and filtration removed one of the viscous components. Calcium depletion made the viscosity particularly susceptible to acidification. The protein fractions were obtained from pooled parotid saliva by ion exchange and gel permeation chromatography procedures. Except for a glycoprotein, these fractions generally exhibited the lowest viscosity in the pH region around their isoelectric points. Calcium generally increased the viscosity of these proteins.