Hypoxia stimulates vesicular ATP release from rat osteoblasts.

Area of Science:

• Cell Biology
• Biochemistry
• Bone Physiology

Background:

• Extracellular adenosine triphosphate (ATP) and its metabolite adenosine diphosphate (ADP) play crucial roles in regulating bone cell function via P2 receptors.
• Specific P2 receptors, such as P2Y(1) and P2Y(2), mediate distinct effects on osteoclast and osteoblast activity, influencing bone remodeling.
• Understanding the mechanisms of extracellular nucleotide release and their impact on bone metabolism is essential for comprehending bone homeostasis.

Purpose of the Study:

• To investigate the constitutive and regulated release of ATP by rat calvarial osteoblasts.
• To determine the mechanism of ATP release, focusing on vesicular exocytosis.
• To examine the effect of hypoxia on osteoblast ATP release and its potential implications for bone cell signaling.

Main Methods:

• Measurement of ATP release from osteoblasts under basal and stimulated conditions.
• Utilized inhibitors of vesicular exocytosis, such as monensin and N-ethylmaleimide, to assess the release mechanism.
• Employed quinacrine staining to visualize and quantify ATP-containing vesicles within osteoblasts.
• Exposed osteoblasts to hypoxia (2% O(2)) to study its effect on ATP release and cell viability.

Main Results:

• Rat calvarial osteoblasts constitutively release ATP, with mature osteoblasts releasing significantly more ATP than undifferentiated cells.
• ATP release is primarily mediated by vesicular exocytosis, as evidenced by inhibition with specific agents and the presence of intracellular ATP vesicles.
• Acute exposure to hypoxia markedly increases osteoblast ATP release without compromising cell viability, suggesting a regulated release mechanism.
• Hypoxia-induced ATP release is significantly attenuated by vesicular exocytosis inhibitors, further supporting this release pathway.

Conclusions:

• Vesicular exocytosis is a key mechanism for the release of biologically significant amounts of ATP from osteoblasts.
• Increased extracellular ATP levels resulting from hypoxia can modulate local purinergic signaling pathways.
• These findings suggest that extracellular ATP signaling in response to oxygen levels may influence the delicate balance between bone formation and resorption, impacting overall bone health.