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Extracellular ATP regulates the proliferation of alveolar macrophages
M Nakanishi1, M Kawasaki, H Ogino
1Second Department of Internal Medicine, Faculty of Medicine, Fukuoka University, Japan.
Abstract:
We examined the effects of extracellular ATP on the proliferation and synthesis of DNA by guinea pig alveolar macrophages (AM). AM proliferated spontaneously in vitro, their number doubling in 72 h. Such proliferation was completely inhibited by adding 1 mM ATP to the culture. The inhibition was dose dependent. ATP also suppressed the spontaneous synthesis of DNA by AM. The inhibitory effect of ATP was not related to cell damage, as the viability and the superoxide anion-generating activity of these cells were unaffected by treatment with ATP for 24 h. The order of potency of the adenosine nucleotides (ATP > ADP > AMP) reflected the character of the P2 purinoceptor. Theophylline inhibited the effect of ATP on the synthesis of DNA by AM to a level produced by the nonhydrolyzable analogue, ATP gamma S, but did not influence the effect of ATP gamma S. These data suggest that the effect of ATP on the synthesis of DNA was exerted mainly via the P2 purinoceptor (82.0%) and to a lesser extent via the P1 purinoceptor (12.6%). We found that small molecules in the lavage fluid inhibited the synthesis of DNA by AM. Thus, the extracellular ATP present in the alveolar lining fluid may participate in controlling the proliferation of AM.
Insights
Extracellular adenosine triphosphate (ATP) inhibits guinea pig alveolar macrophage (AM) proliferation and DNA synthesis. This suggests ATP in lung lavage fluid controls AM growth via purinoceptors.
Area of Science:
- Immunology
- Cell Biology
- Pulmonary Medicine
Background:
- Alveolar macrophages (AM) play a crucial role in lung immunity and homeostasis.
- Spontaneous proliferation of AM in vitro suggests endogenous factors regulate their numbers.
- Understanding the regulation of AM proliferation is vital for respiratory health.
Purpose of the Study:
- To investigate the impact of extracellular adenosine triphosphate (ATP) on guinea pig AM proliferation and DNA synthesis.
- To elucidate the purinoceptor subtypes involved in ATP-mediated regulation of AM.
- To assess the potential role of extracellular ATP in controlling AM populations within the alveolar space.
Main Methods:
- Primary guinea pig AM were cultured in vitro.
- Cell proliferation was assessed by cell counting over 72 hours.
- DNA synthesis was measured using standard assays.
- Cell viability and superoxide anion generation were evaluated to rule out cytotoxic effects.
- Dose-response experiments with various adenosine nucleotides (ATP, ADP, AMP) and analogues (ATPγS) were performed.
- Theophylline was used to differentiate between P1 and P2 purinoceptor involvement.
Main Results:
- AM exhibited spontaneous proliferation in vitro, with cell numbers doubling in 72 hours.
- Extracellular ATP significantly inhibited AM proliferation and DNA synthesis in a dose-dependent manner.
- ATP treatment did not affect AM viability or superoxide anion-generating activity, indicating a non-cytotoxic effect.
- The potency order (ATP > ADP > AMP) and theophylline's effect suggested P2 purinoceptor mediation (82.0%), with a minor contribution from P1 purinoceptors (12.6%).
- Inhibitory substances, including extracellular ATP, were detected in alveolar lavage fluid.
Conclusions:
- Extracellular ATP acts as a potent inhibitor of guinea pig AM proliferation and DNA synthesis.
- The primary mechanism involves the P2 purinoceptor, with a secondary role for the P1 purinoceptor.
- Endogenous extracellular ATP in the alveolar lining fluid may be a key regulator of AM populations in the lungs.
- These findings contribute to understanding the local control of immune cell homeostasis in the pulmonary environment.