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Ionophore-induced functional changes in macrophages
Abstract:
Ca ionophore A 23187 and valinomycin known to induce Ca2+ influx, i.e. K+ efflux, appeared to induce activation-related changes in rat peritoneal macrophages (PM) at 10(-5)-10(-7) M concentrations as revealed by aggregation, nitro blue tetrazolium (NBT) reduction, superoxide anion production as well as beta glucuronidase release; however, lactate dehydrogenase (LDH) activity was measured in supernatants only after treatment with 10(-5) M of A 23187. The PM-activating effect of A 23187 was abolished in the presence of 5 mM EGTA, whereas the activating effect of K ionophore did not depend on the extracellular Ca2+. Fc receptor (FcR) mediated incorporation, intracellular killing as well as the antibody dependent cytotoxicity (ADCC) were markedly inhibited upon incubation with Ca ionophore or valinomycin. C3bR mediated phagocytosis was found to be more resistant to the cation transport affecting drugs. The impairment of effector functions was elicited by nontoxic concentrations of ionophores, however, their inhibiting effects did not require extracellular Ca2+ at the time of ionophore-exposition.
Insights
Calcium ionophores A 23187 and valinomycin activate rat peritoneal macrophages, but inhibit Fc receptor-mediated functions. These ionophores impair effector functions at non-toxic concentrations.
Area of Science:
- Immunology
- Cell Biology
- Pharmacology
Background:
- Ionophores modulate cation transport across cell membranes.
- Calcium (Ca2+) and potassium (K+) ion fluxes are critical for macrophage function.
- Peritoneal macrophages (PM) play a key role in innate and adaptive immunity.
Purpose of the Study:
- To investigate the effects of Ca2+ and K+ ionophores on rat peritoneal macrophage activation and effector functions.
- To determine the role of extracellular calcium in ionophore-induced effects.
Main Methods:
- Treatment of rat peritoneal macrophages with Ca ionophore A 23187 and K+ ionophore valinomycin at varying concentrations.
- Assessment of macrophage activation through aggregation, nitro blue tetrazolium (NBT) reduction, superoxide anion production, and beta-glucuronidase release.
- Measurement of lactate dehydrogenase (LDH) release to assess cytotoxicity.
- Evaluation of Fc receptor (FcR) and C3bR-mediated phagocytosis, intracellular killing, and antibody-dependent cellular cytotoxicity (ADCC).
- Investigation of the role of extracellular calcium using EGTA.
Main Results:
- Both A 23187 and valinomycin induced activation-related changes in PM, including aggregation and release of inflammatory mediators.
- A 23187-induced activation was dependent on extracellular Ca2+, while valinomycin's effect was not.
- FcR-mediated functions (incorporation, intracellular killing, ADCC) were significantly inhibited by both ionophores.
- C3bR-mediated phagocytosis showed greater resistance to ionophore treatment.
- Inhibition of effector functions occurred at non-toxic ionophore concentrations and did not require extracellular Ca2+ during exposure.
Conclusions:
- Cation ionophores can differentially modulate macrophage activation and effector functions.
- Modulation of intracellular cation levels by ionophores significantly impairs FcR-dependent immune responses.
- These findings highlight the complex role of cation homeostasis in macrophage effector mechanisms and suggest potential therapeutic targets.