PTH release stimulated by high extracellular potassium is associated with a decrease in cytosolic calcium in bovine parathyroid cells

We employed the calcium (Ca++)-sensitive, intracellular dye QUIN-2 to examine the role of cytosolic Ca++ in the stimulation of PTH release by high extracellular potassium (K+) concentrations. Addition of 55 mM KCl to cells incubated with 115 mM NaCl and 5 mM KCl lowered cytosolic Ca++ at either low (0.5 mM) extracellular Ca++ (from 194±14 to 159±9 nM, p<.01, N=6) or high (1.5 mM) extracellular calcium (from 465±38 to 293±20 nM, p<.01, N=10). This reduction in cytosolic Ca++ was due to high K+perse and not to changes in tonicity since addition of 55 mM NaCl was without effect while a similar decrease in cytosolic Ca++ occurred when cells were resuspended in 60 mM NaCl and 60 mM KCl. PTH release was significantly (p<.01) greater at 0.5 and 1.5 mM Ca++ in QUIN-2-loaded cells incubated with 60 mM NaCl and 60 mM KCl than in those exposed to 115 mM NaCl and 5 mM KCl. In contrast to most secretory cells, therefore, stimulation of PTH release by high K+ is associated with a decrease rather than an increase in cytosolic Ca++.