Inhibition of rat parotid ecto-ATPase activity.

Area of Science:

• Biochemistry
• Cell Biology
• Pharmacology

Background:

• Ecto-adenosine triphosphate (ATP)ases are enzymes that hydrolyze extracellular ATP.
• Understanding ecto-ATPase activity is crucial for studying ATP signaling in various physiological processes, including exocrine secretion.
• Rat parotid glands are known to respond to extracellular ATP, making them a relevant model for studying ecto-ATPases.

Purpose of the Study:

• To compare the inhibitory profiles of various known and suspected ecto-ATPase inhibitors.
• To determine the potency (IC50 values) of these inhibitors on ecto-ATPase activity in rat parotid plasma membranes.
• To characterize the mechanism of inhibition for selected potent inhibitors.

Main Methods:

• Preparation of rat parotid plasma membranes.
• Assay of ecto-ATPase activity in the presence of different chemical inhibitors.
• Determination of IC50 values for each inhibitor.
• Analysis of inhibition kinetics using Dixon plots for selected inhibitors.

Main Results:

• Several nucleotides and sulfonates showed high IC50 values (above 130 microM), indicating weak inhibition.
• Potent inhibitors with low IC50 values included Reactive Blue 2 (28 microM), ATPgammaS (49 microM), and suramin (72 microM).
• Suramin exhibited non-competitive inhibition, while ATPgammaS and Reactive Blue 2 showed curvilinear inhibition patterns.

Conclusions:

• Reactive Blue 2, ATPgammaS, and suramin are potent inhibitors of ecto-ATPase in rat parotid membranes.
• These inhibitors demonstrate varying mechanisms of action on ecto-ATPase.
• The study provides valuable data for selecting appropriate inhibitors to study ecto-ATPase function in exocrine tissues.