Interleukin-10 expression is induced by increase of intracellular calcium levels in the monocytic cell line U937

The regulation of interleukin-10 (IL-10) expression after treatment with a high, exponential, electric pulse was investigated in the monocytic cell line U937. Recently, we showed IL-10 protein production in the monocytic cell lines U937 and THP-1 after exposure to a single, high exponential electric pulse [Lehmann MH, Höffken K, Berg H (1996) Bioelectrochem. Bioenerg. 41: 227-229]. In the present study, the specificity of this process was proven by semiquantitative reverse-transcriptase polymerase chain reaction. It was found that the presence of calcium in the culture medium during the pulse is essential for IL-10 protein production. Only a small amount of IL-10 protein was produced in calcium free medium. The calcium specific chelator EGTA prevented IL-10 protein production induced by the electric pulse in a dose-dependent manner. Additionally, IL-10 mRNA transcription could be induced in U937 cells without pulse application by means of the calcium ionophore ionomycin. No IL-10 protein could be detected by ELISA. However, down-regulation of TNF-alpha mRNA levels after ionomycin stimulation provided an indirect proof that IL-10 protein production occurred.