Spontaneous oscillations of intracellular XXXX in single @entity291 parathyroid cells may be associated with the inhibition of parathyroid hormone secretion.

@entity268 @entity3740 @entity3044 @entity24585 @entity5154 @entity460 @entity141 @entity291
@entity24585 secretion is tightly regulated by extracellular @entity460 ([ @entity141 ]e) and in turn regulates @entity460 homeostasis through its action on target tissues. We investigated the mechanism and physiological significance of intracellular @entity460 ([ @entity141 ]i) levels in relation to the secretion of @entity24585 in single @entity291 parathyroid cells. [ @entity141 ]i was recorded using digital imaging microscopy, and secretion of @entity24585 was correlated in the same cell using the reverse hemolytic plaque assay. In individual parathyroid cells, oscillations of [ @entity141 ]i were present in response to specific stimuli. Like secretory activity, response to [ @entity141 ]e concentrations was heterogeneous. Oscillations of [ @entity141 ]i occurred spontaneously in 22% of cells at inhibitory concentrations of [ @entity141 ]e. Oscillations were present only in high [ @entity141 ]e (> or = 1.8 mM) and not noted at lower concentrations of [ @entity141 ]e. The interval and amplitude of [ @entity141 ]i oscillations were 42 +/- 2 sec, and 20 +/- 1 nM (mean +/- SE), respectively. Oscillations were rapidly abolished when [ @entity141 ]e was removed by EGTA, and this effect was reversible. Addition of Mg2+ or polycationic antibiotics such as @entity5154 resulted in an [ @entity141 ]i spike, but oscillations were absent. @entity3740 , which blocks @entity141 influx through @entity460 channels in various cells, rarely caused oscillations even in the presence of high concentrations of [ @entity141 ]e. To test the role of @entity268 in [ @entity141 ]i oscillations, we added the beta-agonist @entity3044 . The addition of @entity3044 , however, did not cause oscillations. The number of cells that released @entity24585 was significantly lower in cells with oscillations compared with cells without oscillations. We suggest that spontaneous [ @entity141 ]i oscillations are due to the influx of [ @entity141 ]e through ion channels rather than release from [ @entity141 ]i stores and may be a specific intracellular signal associated with inhibition of @entity24585 secretion.
