Macrophage migration inhibitory factor-induced Ca2+ response in rat testicular peritubular cells

Macrophage migration inhibitory factor (MIF), originally described as a T-c ell product, has recently been identified in several endocrine organs. In t he rat testis, MIF is secreted by the Leydig cells into testicular intersti tial fluid that directly contacts Sertoli and peritubular cells. To investi gate whether MIF is involved in calcium-dependent signal transduction, we h ave isolated rat Sertoli and peritubular cells. Despite progress in underst anding functional properties of MIF, the molecular mechanism of MIF action in target cells is almost completely unknown. Here we find that recombinant MIF evokes a transient increase in calcium levels in peritubular cells but not in Sertoli cells from dissociated rat testis. Concentrations in the ra nge between 12.5 ng/ml and 120 ng/ml of recombinant MIF were found to be ef fective, with 50 ng/ml yielding the largest increase in intracellular calci um. Preincubation of MIF with a neutralizing monoclonal antibody specifical ly blocked the response. Incubation of the peritubular cells in calcium-fre e buffer clearly decreased the evoked response in intracellular calcium con centration. However, the calcium response was greatly decreased by thapsiga rgin, an inhibitor of the Ca2+ ATPase of the endoplasmic reticulum. The res ults strongly indicate that calcium is mobilized from reticulum stores duri ng MIT-mediated signal transduction in the testis. In conclusion, our resul ts provide the first characterization of MIF signal transduction in the tes tis and suggest that signaling from Leydig cells to peritubular cells throu gh MlF is mediated by receptors coupled to release of intracellular calcium .