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 indu ced changes in cell counts or functional responses while information regard ing intracellular signal transduction parameters is lacking. Therefore in t he present study we investigated in granulocytes the regulation of intracel lular calcium ([Ca2+](i)) which is an important intracellular second messen ger. 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 u sing the Ca2+ sensitive fluorescent dye Fura-2, while the oxidative burst a nd phagocytosis were measured by flow cytometry. While resting [Ca2+](i), l evels were unchanged, the Ca2+ transient induced N-formyl-methionyl-leucyl phenylalanine (fMLP) and platelet activating factor (PAF) were enhanced 1 h our after the test compared to pre-exercise values although fMLP receptor d ensity 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 regul ation of Ca2+ signaling in granulocytes. The potentiation of Ca2+ signals i s not accompanied by an enhancement of cellular functional parameters sugge sting a blockade in intracellular signalling pathways.