Permeabilization reveals classical stimulus-secretion coupling in bovine parathyroid cells.

Area of Science:

• Endocrinology
• Cell Biology
• Physiology

Background:

• High extracellular calcium typically stimulates hormone release in most secretory cells.
• Parathyroid hormone (PTH) release is uniquely inhibited by high extracellular calcium in intact parathyroid cells.

Purpose of the Study:

• To investigate the unique secretory apparatus of parathyroid cells.
• To elucidate the mechanisms underlying calcium-regulated PTH release.

Main Methods:

• Development of electroshock-induced permeabilization technique for bovine parathyroid cells.
• Assessment of plasma membrane integrity using trypan blue uptake and 86Rb efflux.
• Measurement of PTH release from permeabilized cells under varying calcium concentrations.

Main Results:

• Permeabilized parathyroid cells demonstrated a 2.8-fold increase in PTH release with high calcium (10(-5) to 4 X 10(-4) M), mimicking classical stimulus-secretion coupling.
• PTH release was low at calcium concentrations mimicking low extracellular levels in intact cells (approximately 2 X 10(-7) M).
• Diacylglycerol and protein kinase C activators (dioctanoylglycerol and 12-O-tetradecanoyl phorbol 13-acetate) enhanced PTH release in permeabilized cells at low calcium levels.

Conclusions:

• Cellular mechanisms independent of cytosolic calcium concentration changes likely mediate low calcium-stimulated PTH release in intact parathyroid cells.
• Diacylglycerol and protein kinase C may play a significant role in regulating PTH secretion under low extracellular calcium conditions.