Modulation of intracellular Ca 2+ in the parathyroid cell : Release of Ca 2+ from non-mitochondrial pools by inositol trisphosphate

Abstract

Stimuli which enhance secretion from parathyroid cells such as low extracellular Ca 2+ or Mg 2+ are associated with a decrease in the cytosolic Ca 2+ concentration as measured by quin2. Current evidence suggests that increased production of inositol 1,4,5-triphosphate (IP 3) releases Ca 2+ from cellular stores thus increasing cytosolic Ca 2+. We used saponin-permeabilized dispersed bovine parathyroid cells to study the effect of IP 3 on intracellular Ca 2+. IP 3 released Ca 2+ from these cells in a dose-dependent manner; half-maximal response occurred with 0.3 μM IP 3 and maximal response with 1.2 μM IP 3. Permeabilized cells incubated in the presence of the mitochondrial inhibitor antimycin A released a similar amount of Ca 2+ suggesting that IP 3 releases Ca 2+ from a non-mitochondrial pool. These results suggest that IP 3 regulates cytosolic Ca 2+ in this system and may function as a second messenger controlling hormone secretion.