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Pretreatment with phorbol esters abrogates mast cell adenosine responsiveness
1Department of Medicine, University of California San Diego Medical Center 92103.
Abstract:
Adenosine potentiates preformed mediator release from mouse bone marrow-derived mast cells stimulated with specific Ag or the calcium ionophore A23187. When these mast cells were cultured for 30 to 120 min with the phorbol ester PMA (10(-8) or 10(-7) M), protein kinase C activity was increased and Ag-stimulated beta-hexosaminidase release was modestly inhibited, whereas A23187-stimulated release was synergistically enhanced. However, in both cases, exogenous adenosine failed to augment beta-hexosaminidase release. Overnight PMA exposure produced a decrease in protein kinase C activity and a decrease in both Ag- and A23187-stimulated preformed mediator release, as well as a lack of responsiveness to adenosine. This hyporesponsiveness could be reversed by 24 h after washing the cells free of PMA. The generation of the arachidonic acid metabolite leukotriene C4 was not altered by mast cell PMA exposure. The ability of adenosine to increase intracellular cAMP concentrations was modestly blunted by high doses of PMA, and PMA abrogated the increase in intracellular free calcium levels usually observed in cells stimulated with Ag in the presence of 10(-5) M adenosine. PMA exposure induces a hyporesponsiveness to adenosine in mast cells, either by a direct effect on protein kinase C activity and/or by an effect on adenosine receptor expression or recycling.
Insights
Phorbol ester PMA exposure in mouse mast cells alters responses to adenosine. Short-term PMA enhances some responses, while long-term exposure causes adenosine hyporesponsiveness, impacting mediator release.
Area of Science:
- Immunology
- Cell Biology
- Pharmacology
Background:
- Adenosine modulates mast cell mediator release.
- Mast cells play a key role in allergic and inflammatory responses.
Purpose of the Study:
- To investigate the effect of phorbol ester PMA on adenosine-mediated mast cell activation.
- To understand the mechanisms underlying changes in mast cell responsiveness to adenosine.
Main Methods:
- Mouse bone marrow-derived mast cells were cultured with phorbol ester PMA.
- Stimulation with antigen (Ag) or calcium ionophore A23187 was performed.
- Beta-hexosaminidase release, protein kinase C activity, and intracellular signaling (cAMP, calcium) were measured.
Main Results:
- Short-term PMA increased protein kinase C activity, inhibiting Ag-stimulated release but enhancing A23187-stimulated release.
- Long-term PMA exposure decreased protein kinase C activity and led to adenosine hyporesponsiveness.
- PMA affected adenosine's ability to increase cAMP and abrogated calcium influx.
Conclusions:
- PMA exposure induces adenosine hyporesponsiveness in mast cells.
- This hyporesponsiveness may involve direct effects on protein kinase C or adenosine receptor regulation.
- Understanding these interactions is crucial for inflammatory disease research.