Excessive Accumulation of Intracellular Ca After Acute Exercise Potentiated Impairment of T-cell Function

Ca is an important intracellular second messenger known to regulate several cellular functions. This research aimed to investigate the mechanisms of exercise-induced immunosuppression by measuring intracellular calcium levels, Ca-regulating gene expression, and agonist-evoked proliferation of murine splenic T lymphocytes. Mice were randomly assigned to the control, sedentary group (C), and three experimental groups, which performed a single bout of intensive and exhaustive treadmill exercise. Murine splenic lymphocytes were separated by density-gradient centrifugation immediately (E0), 3h (E3), and 24h after exercise (E24). Fura-2/AM was used to monitor cytoplasmic free Ca concentration in living cells. The combined method of carboxyfluorescein diacetate succinimidyl ester (CFSE) labeling and flow cytometry was used for the detection of T cell proliferation. The transcriptional level of Ca-regulating genes was quantified by using qPCR. Both basal intracellular Ca levels and agonist (ConA, OKT3, or thapsigargin)-induced Ca transients were significantly elevated at E3 group (<0.05 vs. control). However, mitogen-induced cell proliferation was significantly decreased at E3 group (<0.05 vs. control). In parallel, the transcriptional level of plasma membrane Ca-ATPases (PMCA), sarco/endoplasmic reticulum Ca-ATPases (SERCA), TRPC1, and P2X7 was significantly downregulated, and the transcriptional level of IPR2 and RyR2 was significantly upregulated in E3 (<0.01 vs. control). In summary, this study demonstrated that acute exercise affected intracellular calcium homeostasis, most likely by enhancing transmembrane Ca influx into cells and by reducing expression of Ca-ATPases such as PMCA and SERCA. However, altered Ca signals were not transduced into an enhanced T cell proliferation suggesting other pathways to be responsible for the transient exercise-associated immunosuppression.