TY - JOUR
T1 - Ca2+-induced increases in steady-state concentrations of intracellular calcium are not required for inhibition of parathyroid hormone secretion
AU - Russell, J.
AU - Zhao, W.
AU - Christ, G.
AU - Ashok, S.
AU - Angeletti, R. H.
PY - 1999/6
Y1 - 1999/6
N2 - It has been well established, that increases in extracellular calcium concentration ([Ca2+]) inhibit parathyroid, hormone (PTH) secretion. The effects of [Ca2+] are mediated through a G-protein-coupled receptor that has been cloned and characterized. Additionally, it has been demonstrated in parathyroid cells that an increase in [Ca2+] results in an increase in steady-state levels of intracellular calcium ([Ca2+]i). At present, it has not been fully resolved whether changes in [Ca2+]i are related to changes in PTH secretion. In the current study, the effect of increased [Ca2+] on PTH secretion and the connection regarding changes in concentrations of intracellular calcium [Ca2+]i have been examined in primary cultures of bovine parathyroid cells. PTH secretion was measured by radioimmunoassay and intracellular calcium was determined by single cell calcium imaging. Bovine parathyroid cells pre-incubated with either 0.5 or 1 mM calcium responded to rapid increases in [Ca2+] (≥0.5 mM) with an immediate and sustained increase in steady-state levels of [Ca2+], that persisted for time intervals greater than 15 minutes. Although the magnitude of the sustained increase in [Ca2+]i varied among individual cells (∼40% to > 300%), the overall pattern and course of time were similar in all cells examined (n = 142). In all trials, [Ca2+], immediately returned to baseline levels following the addition of the calcium chelator, 1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid (BAPTA). Additional control studies, however, suggest that sustained increases in [Ca2+], do not correlate with regulation of parathyroid hormone secretion. Sustained elevations of [Ca2+]i were not observed when [Ca2+] was gradually increased by the addition of 0.1 mM increments at 1 minute intervals. Furthermore, the effect on inhibition of PTH secretion was the same regardless of whether [Ca2+] was increased, by gradual or rapid addition.
AB - It has been well established, that increases in extracellular calcium concentration ([Ca2+]) inhibit parathyroid, hormone (PTH) secretion. The effects of [Ca2+] are mediated through a G-protein-coupled receptor that has been cloned and characterized. Additionally, it has been demonstrated in parathyroid cells that an increase in [Ca2+] results in an increase in steady-state levels of intracellular calcium ([Ca2+]i). At present, it has not been fully resolved whether changes in [Ca2+]i are related to changes in PTH secretion. In the current study, the effect of increased [Ca2+] on PTH secretion and the connection regarding changes in concentrations of intracellular calcium [Ca2+]i have been examined in primary cultures of bovine parathyroid cells. PTH secretion was measured by radioimmunoassay and intracellular calcium was determined by single cell calcium imaging. Bovine parathyroid cells pre-incubated with either 0.5 or 1 mM calcium responded to rapid increases in [Ca2+] (≥0.5 mM) with an immediate and sustained increase in steady-state levels of [Ca2+], that persisted for time intervals greater than 15 minutes. Although the magnitude of the sustained increase in [Ca2+]i varied among individual cells (∼40% to > 300%), the overall pattern and course of time were similar in all cells examined (n = 142). In all trials, [Ca2+], immediately returned to baseline levels following the addition of the calcium chelator, 1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid (BAPTA). Additional control studies, however, suggest that sustained increases in [Ca2+], do not correlate with regulation of parathyroid hormone secretion. Sustained elevations of [Ca2+]i were not observed when [Ca2+] was gradually increased by the addition of 0.1 mM increments at 1 minute intervals. Furthermore, the effect on inhibition of PTH secretion was the same regardless of whether [Ca2+] was increased, by gradual or rapid addition.
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U2 - 10.1006/mcbr.1999.0135
DO - 10.1006/mcbr.1999.0135
M3 - Article
C2 - 10425230
AN - SCOPUS:0033139682
SN - 1522-4724
VL - 1
SP - 221
EP - 226
JO - Molecular Cell Biology Research Communications
JF - Molecular Cell Biology Research Communications
IS - 3
ER -