Stimulating effect of erythropoietin on thymocyte energetics revealed in vitro by potential-sensitive fluorescent probe

Various tissue-specific hormones, including erythropoietin, are known to produce stimulating side effect on immune cells. Earlier studies employing potential-sensitive probes revealed positive correlation between the activity of blood lymphocytes and energetic state of mitochondria. In this study we used a fluorescent cationic probe 4-(p-dimethylaminostyryl)-1-methylpyridinium (DSM) so that to quantify erythropoietin effects on rat thymus lymphocytes (TL) in vitro. As was shown previously, DSM accumulates in energized mitochondria and its fluorescence depends on the transmembrane electric potential of plasma and mitochondrion membranes, as well as on the number of mitochondria. DSM fluorescence intensity (FDSM) was recorded in individual T-cells before and after 30-min incubation with erythropoietin (0.2-200 U/ml) at 37°C. Our cytofluorimetric data revealed a statistically significant increase of mean FDSM and the number of energized mitochondria in TL incubated with erythropoietin (2 U/ml) as compared with control cells. Besides, erythropoietin increased voltage difference across plasma membrane. The effect depended on erythropoietin concentration and on the initial state of TL mitochondria. The responses of TL recorded by means of DSM may serve as adequate characteristics of individual differences of thymocytes and as a general estimate of thymus physiological state.