The flow-rate-dependent excretion of ionized calcium in human parotid saliva.

The total calcium content of parotid saliva is increased in various diseases. Because of methodological difficulties, little is known about the ionized calcium fraction although it might be of importance for the secretion of fluid and proteins. Using a new method with calcium-selective disc electrodes, which gives an easy and exact estimation of ionized calcium, the Ca²⁺ activity in pilocarpine-stimulated parotid saliva of 10 healthy males was measured. With increasing flow-rate (0.1–0.6 ml/min), the concentration of ionized calcium rose exponentially from 1.13 ± 0.36 mequiv./litre (0.57 ± 0.18 mmol/litre) to 1.76 ± 0.21 mequiv./litre. At higher flow-rates (up to 2.5 ml/min), a plateau was observed. The total calcium concentration and the ionic calcium concentration were closely correlated (r = 0.93) and the ratio ionic/total remained nearly constant at 0.54 at all flow-rates.