Decoupling of intracellular calcium signaling in granulocytes after exhaustive exercise

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.