Expression of phosphate and calcium transporters and their regulators in parotid glands of mice

The concentration of inorganic phosphate (Pi) in plasma is under hormonal control, with deviations from normal values promptly corrected to avoid hyper- or hypophosphatemia. Major regulators include parathyroid hormone (PTH), fibroblast growth factor 23 (FGF-23), and active vitamin D 3 (calcitriol). This control is achieved by mechanisms largely dependent on regulating intestinal absorption and renal excretion, whose combined actions stabilise plasma Pi levels at around 1–2 mM. Instead, Pi concentrations up to 13 and 40 mM have been measured in saliva from humans and ruminants, respectively, suggesting that salivary glands have the capacity to concentrate Pi. Here we analysed the transcriptome of parotid glands, ileum, and kidneys of mice, to investigate their potential differences regarding the expression of genes responsible for epithelial transport of Pi as well as their known regulators. Given that Pi and Ca 2+ homeostasis are tightly connected, the expression of genes involved in Ca 2+ homeostasis was also included. In addition, we studied the effect of vitamin D 3 treatment on the expression of Pi and Ca 2+ regulating genes in the three major salivary glands. We found that parotid glands are equipped preferentially with Slc20 rather than with Slc34 Na + /Pi cotransporters, are suited to transport Ca 2+ through the transcellular and paracellular route and are potential targets for PTH and vitamin D 3 regulation.