Alteration by ouabain of rat submandibular glands function

The zinc receptor, ZnR/GPR39, modulates taste sensitivity by regulating ion secretion in mouse salivary gland

Reduced saliva secretion, dry mouth, and loss of taste are debilitating symptoms associated with zinc deficiency. A mechanism for zinc regulation of these processes is lacking. Here, we identified the Zn2+ sensing receptor ZnR/GPR39 as a mediator of ion transport in salivary gland epithelium. By monitoring transport of NH4 +, a surrogate for K+, we revealed that Zn2+ upregulates the Na+/K+ ATPase pump activity in parotid and submandibular salivary gland epithelium from wildtype (WT), but not from ZnR/GPR39 knockout (KO), mice. Since Na+/K+ ATPase activity is crucial for solute transport, we compared saliva composition in WT and ZnR/GPR39 KO mice and found impaired ionic concentration and reduced saliva secretion in ZnR/GPR39 KO mice. Moreover, mice deficient in ZnR/GPR39 exhibited decreased sensitivity to appetitive Na+ concentrations. Altogether, we demonstrate that salivary ZnR/GPR39 activity controls saliva ion composition and secretion, and provides a target for therapeutic approaches for dry mouth and taste disorders.

Ionic composition of rat airway surface liquid determined by X-ray microanalysis

The thin layer of liquid that lines the conducting airway epithelium, the airway surface liquid (ASL), is important for mucociliary clearance. Altered ionic composition and/ or volume of the ASL play a major role in the pathology of airway diseases such as cystic fibrosis. Since the ASL is a thin layer, it has been difficult to exactly determine its composition. The present paper describes two techniques that have been developed and used to study ASL composition: X-ray microanalysis of frozen hydrated rat trachea, and an ion-exchange (dextran) bead method, where dextran beads were placed on the airway epithelium to equilibrate with the ASL; the beads were then collected under silicone oil, dried and analyzed by X-ray microanalysis. The results from both frozen-hydrated specimens and from the dextran beads showed that ASL from rat trachea is hypotonic. Concentrations of Na, P, S, and K were higher in the frozen-hydrated ASL, in which mainly the mucus layer is analyzed, compared with the dextran bead method, in which mainly the periciliary liquid is sampled. Also the composition of rat nasal fluid was investigated by the dextran bead method. This fluid was somewhat hypertonic because of a high K concentration. The ionic composition of the nasal and tracheal fluid can be manipulated by cholinergic or alpha- or beta-adrenergic stimulation. Collecting ASL with dextran beads did not disturb the integrity of the airway epithelium. The ionic composition of the collected beads remained stable for several days during storage in silicone oil. It is concluded that X-ray microanalysis is a suitable method to determine the ionic composition of ASL.