Decoupling of Intracellular Calcium Signaling in Granulocytes After Exhaustive Exercise

Abstract

There is growing evidence that exhaustive exercise can induce a suppression of the innate immune functions. Most studies so far describe exercise induced changes in cell counts or functional responses while information regarding intracellular signal transduction parameters is lacking. Therefore in the present study we investigated in granulocytes the regulation of intracellular calcium ([Ca2+]i) which is an important intracellular second messenger. Healthy volunteers underwent a treadmill exercise test at 80% of their maximal oxygen uptake until exhaustion. Granulocytes were separated before and 1 hour after the test. [Ca2+]i was analyzed spectrophotometrically using the Ca2+ sensitive fluorescent dye Fura-2, while the oxidative burst and phagocytosis were measured by flow cytometry. While resting [Ca2+]i levels were unchanged, the Ca2+ transient induced N-formyl-methionyl-leucyl phenylalanine (fMLP) and platelet activating factor (PAF) were enhanced 1 hour after the test compared to pre-exercise values although fMLP receptor density did not change. In contrast, oxidative burst and phagocytosis evoked by fMLP and phorbol-myristate-acetate (PMA) were decreased after exercise. Together, our data support the view that exhaustive exercise affects regulation of Ca2+ signaling in granulocytes. The potentiation of Ca2+ signals is not accompanied by an enhancement of cellular functional parameters suggesting a blockade in intracellular signalling pathways.

Exercise delays neutrophil apoptosis by a G-CSF-dependent mechanism

“…Focusing in cellular mechanisms, our data suggest that apoptosis delay is mediated on a cellular level by [Ca 2ϩ ] i . After both marathon run and treadmill exercises, ligand-induced calcium transients were enhanced, confirming our previous results (29). Mobilization of intracellular calcium has been recognized as an important mechanism in receptormediated activation of neutrophils known to precede apoptosis delay.…”

“…During recording, cells were stimulated with Nformyl-methionyl-leucyl-phenylalanin and continuously stirred at 28°C. [Ca 2ϩ ]i was calculated as previously described (29).…”

Exercise, Immunity, and Illness

“…1.5 h) exercise (Chinda et al, 2003;Suzuki et al, 2003;Davison and Gleeson, 2005Laing et al, 2008;Davison and Diment, 2010). This decline in killing capacity has not been coupled to changes in cell surface receptors, suggesting that the modulatory effects of exercise on in vitro stimulants occur downstream in intracellular signal transduction pathways of neutrophils such as phosphorylation cascades or secondary messengers (e.g., cyclic adenosine monophosphate, calcium) (Mooren et al, 2001;Peake, 2002). The magnitude of the effects of prolonged exercise on neutrophil effector functions will depend on the balance of immunosuppressive (e.g., "refractory period") and immunostimulating factors (e.g., priming agents) which largely depend on the extent of neutrophilia (Peake, 2002).…”

Agonists of proteinase-activated receptor-2 modulate human neutrophil cytokine secretion, expression of cell adhesion molecules, and migration within 3-D collagen lattices

“…Freshly isolated neutrophils (5ϫ10 5 -1ϫ10 6 ) were incubated in a buffer containing 140 mM NaCl, 3 mM KCl, 0.4 mM Na 2 HPO 4 , 10 mM HEPES, 5 mM glucose, 1 mM MgCl 2 , and 1.8 mM CaCl 2 with 5-8 M Fura-2/AM for 30 min at room temperature as described previously [21]. Fluorescence was measured in cell suspensions using a cuvette spectrofluorimeter (Deltascan, PTI, NJ) and appropriate software (Deltascan, PTI), as described previously [21]. Fluorescence was measured at excitation wavelengths of 340 nm and 380 nm, and emitted light was monitored at 510 nm.…”