Alterations in intracellular calcium signaling of lymphocytes after exhaustive exercise

Exhaustive exercise is accompanied by pronounced quantitative changes in leukocytes. Whereas most studies on lymphocytes have concentrated on their proliferative responses or cytokine secretion, not much is known about exercise-induced changes in intracellular signal transduction processes. In lymphocytes, the concentration of intracellular free calcium ([Ca(2+)](i)) is an important intracellular second messenger linking extracellular stimuli to cellular responses. The aim of the present study was to examine the effect of exhaustive exercise on the calcium homeostasis of lymphocytes.

Healthy volunteers underwent treadmill exercise at 80% of their maximal oxygen uptake until exhaustion. Blood samples were taken before, immediately after, 1 h after, and 1 d after the test. Lymphocyte subsets were analyzed by flow cytometry; isolation of lymphocytes was performed by density gradient centrifugation. [Ca(2+)](i) was measured using the calcium-sensitive fluorescent dye Fura-2.

Compared with preexercise conditions, basal [Ca(2+)](i) was increased immediately after exercise, whereas there was no change after 1 h or 1 d. The anti-CD3- and phytohemagglutinin-induced Ca(2+) responses demonstrated a bivalent pattern. Immediately after exercise, Ca(2+) transients were impaired, whereas 1 h after and 1 d after the test, the Ca(2+) responses were increased. In contrast, the Ca(2+) responses induced by thapsigargin were not different at any time interval. Lymphocyte subsets increased immediately after exercise, especially natural killer cells and CD8+ T cells, and decreased below preexercise levels after 1 h. One day after exercise, cell counts were not different from preexercise levels.

Taken together, this novel approach demonstrates that exhaustive exercise has a profound influence on intracellular calcium signaling of lymphocytes. These effects may explain changes in lymphocyte function that have previously been reported.