Ca-ATPase activity in bovine parathyroid cells.

Area of Science:

• Biochemistry
• Cell Biology
• Endocrinology

Background:

• Parathyroid glands are sensitive to extracellular calcium.
• Cytosolic calcium may mediate parathyroid hormone secretion.
• Ca-ATPase is a potential regulator of cytosolic calcium.

Purpose of the Study:

• Investigate the presence and characteristics of Ca-ATPase in parathyroid cells.
• Determine the role of Ca-ATPase in calcium homeostasis and hormone secretion.

Main Methods:

• Utilized high-performance liquid chromatography (HPLC) to measure ADP formation from ATP.
• Assayed enzyme activity in parathyroid cell homogenates under various conditions (calcium, EGTA, ouabain).
• Tested the effects of calmodulin inhibitors, monovalent cations, magnesium, and azide on enzyme activity.

Main Results:

• Identified calcium-dependent Ca-ATPase activity with two Km (Ca) values (31 and 853 nM).
• High-affinity Ca-ATPase activity was inhibited by trifluoperazine and stimulated by monovalent cations and magnesium.
• Sodium significantly increased Ca-dependent ATPase activity, while azide showed differential inhibition on Mg-dependent vs. Ca-dependent activity.

Conclusions:

• Bovine parathyroid cells possess a high-affinity Ca-ATPase with a Km relevant to cytosolic calcium concentrations.
• Ca-ATPase likely plays a crucial role in regulating cytosolic calcium and, consequently, parathyroid hormone secretion.