Figure 1.

The calciostat in parathyroid cells. Left: A representation of the feedback mechanism by which PTH elevates the serum^* Ca²⁺ concentration and Ca²⁺ feeds back on the parathyroid to suppress PTH secretion in a process mediated by the CaSR. Right: Human parathyroid cells were perifused with HEPES-buffered physiological saline solutions containing various Ca²⁺ concentrations and samples of perifusate were collected at various times and subsequently analyzed for PTH1–84 as described in Conigrave et al. (2004). The results have been re-drawn. ^*Total and ionized calcium concentrations are comparable in serum and plasma since the major calcium-binding protein, albumin is present in similar concentrations in both these fluids.