We have previously presented evidence that parathyroid cells contain voltage-independent calcium channels and that the function of these channels is to provide a pathway for calcium to enter the intracellular compartment and affect the rate of secretion of parathyroid hormone (PTH). We have now measured PTH secretion in the presence of various channels agonists and antagonists to confirm the presence of the calcium channels. Addition of either of the agonists Bay-K-8644 or (+)202-791 resulted in increased calcium uptake and reduced PTH secretion, whereas the antagonist (-)202-791 caused reduced calcium uptake and increased PTH secretion. Also depolarization of parathyroid cells by applying 50 mM potassium to the extracellular solution increased PTH secretion, and this increased secretion was not altered by either the agonist(+)202-791 or the antagonist (-)202-791. This suggests that the effect of depolarization was to reduce the intracellular calcium concentration enough to saturate PTH secretion. Overall, the experiments with the calcium channel agonists and antagonists confirmed the presence of calcium channels in parathyroid cells and their role in affecting PTH secretion.
