Abstract
Appropriate composition of oral saliva is essential for a healthy milieu that protects mucosa and teeth. Only few studies, with small sample numbers, investigated physiological saliva ion composition in humans. We determined saliva ion composition in a sufficiently large cohort of healthy adults and analyzed the effect of physiological stimulation. We collected saliva from 102 adults under non-stimulated and physiologically stimulated conditions (chewing). Individual flow rates, pH, osmolality, Na(+), K(+), Cl(-), and HCO(3)(-) concentrations under both conditions as well as the individual changes due to stimulation (Δvalues) were determined. Non-stimulated saliva was hypoosmolal and acidic. Na(+), Cl(-), and HCO(3)(-) concentrations remained well below physiological plasma values, whereas K(+) concentrations exceeded plasma values more than twofold. Stimulation resulted in a doubling of flow rates and substantial increases in pH, HCO(3)(-), and Na(+) concentrations. Overall, stimulation did not considerably affect osmolality nor K(+) or Cl(-) concentrations of saliva. An in-depth analysis of stimulation effects, using individual Δvalues, showed no correlation of Δflow rate with Δion concentrations, indicating independent regulation of acinar volume and ductal ion transport. Stimulation-induced Δ[Na(+)] correlated with Δ[HCO(3)(-)] and Δ[Cl(-)] but not with Δ[K(+)], indicating common regulation of ductal Na(+), Cl(-), and HCO(3)(-) transport. We present a robust data set of human oral saliva ion composition in healthy adults and functional insights into physiological stimulation. Our data show (i) that flow-dependence exists for Na(+) and HCO(3)(-) but not for K(+) and Cl(-) concentrations, (ii) osmolality is flow-independent, (iii) regulation of Na(+), Cl(-), and HCO(3)(-) transport is coupled, (iv) regulation of flow rate and ion concentrations are independent and (v) spatially separated between acini and ducts, respectively.