Potassium stimulates parathyroid hormone release in the absence of extracellular calcium

Potassium-stimulated release of many hormones requires the presence of extracellular calcium. At variance with this mechanism, potassium-evoked parathyroid hormone (PTH) release from perifused dispersed bovine parathyroid cells also occurred in calcium-free medium containing 1 mM EGTA. Tetraethylammonium, which presumably suppresses the efflux of potassium from parathyroid cells, also stimulated PTH secretion. Removal of sodium did not suppress potassium-stimulated PTH secretion, but inhibited the release of the hormone evoked by calcium removal and by isoproterenol. Ouabain, on the other hand, suppressed the release of PTH evoked by calcium removal and by potassium, but not by isoproterenol. Unlike high potassium and removal of calcium, isoproterenol caused a parallel increase in cAMP release. In conclusion, PTH secretion is reversibly stimulated by potassium in the absence of extracellular calcium. Our findings suggest that potassium stimulates PTH secretion by a unique mechanism the nature of which remains to be elucidated.