Bovine parathyroid cells were used to study parathyroid hormone (PTH) release and the cytoplasmic Ca2+ concentration (Ca2+ 1). When the extracellular Ca2+ concentration was decreased from 3.0 to 0.5 mM, perifused cells reacted with rapid stimulation of PTH release. However, a further reductionof extracellular Ca2+ to < 10 nM resulted in prompt inhibition. Both effects were readily reversible. Using the intracellular Ca2+ indicator quin-2 also as a buffer for calcium it was possible to control Ca2+ 1 within the 20–600 nM range. PTH release was found to increase with Ca2+ up to 200 nM but was gradually suppressed above this concentration.
