Reconstitution of Calcium-Regulated Parathyroid Hormone Secretion from Streptolysin-O-Permeabilized Parathyroid Cells by Guanosine 5′-O-(Thio)Triphosphate1

• Published in: Endocrinology (Philadelphia) Vol. 138; no. 3; pp. 1170 - 1179
• Main Authors: Matovcik, Lisa M, Rhee, Steven S, Schaefer, Jean F, Kinder, Barbara K
• Format: Journal Article
• Language: English
• Published: Endocrine Society 01-03-1997
• ISSN: 0013-7227; 1945-7170
• DOI: 10.1210/endo.138.3.4971

Intracellular Ca2+ levels determine the amount of PTH
secretion from parathyroid cells. Dissociated calf parathyroid cells
were permeabilized with streptolysin-O (SLO) to provide an in
vitro model system to examine Ca2+-dependent
regulation of hormone secretion. PTH release from these cells was
energy dependent and increased by cytosolic cofactors. Guanosine
5′-O-(thio)triphosphate (GTPγS) increased PTH
secretion from SLO-permeabilized cells in a dose-dependent manner from
0.1–100 μm. In the absence of GTPγS there was no
relationship between the ambient Ca2+ concentration and the
rate of PTH secretion. However, in the presence of GTPγS,
intracellular Ca2+ inhibited PTH secretion with an
EC50 of approximately 0.1 μm, corresponding
to physiological intracellular Ca2+ levels. Thus, the
addition of GTPγS to SLO-permeabilized parathyroid cells
reconstituted the inverse relationship between extracellular
Ca2+ and PTH secretion that is observed in
vivo and in intact cells. The data indicate that this effect is
mediated at least in part by heterotrimeric guanosine triphosphatases.
In addition, calcium/calmodulin-dependent protein kinase II appears to
mediate low Ca2+-dependent PTH secretion from these cells.