Differential Regulation of Intracellular Signaling Systems by Sodium Fluoride in Rat Glioma Cells

We investigated the rapid and slow effects of NaF on intracellular signaling systems such as Ca 2+ homeostasis and cyclic GMP (cGMP) generation in rat glioma C6 cells, using the Ca 2+ ‐sensitive dye fura‐2 and cGMP enzyme immunoassay. We found that the following: (a) NaF enhanced cGMP generation in a concentration‐dependent manner. This enhancement was abolished by pretreatment with 100 µ M BAPTA tetraacetoxymethyl ester or in the presence of W‐7 in a concentration‐dependent manner. N G ‐Monomethyl‐ l ‐arginine (NMMA), a competitive inhibitor of nitric oxide synthase (NOS), also inhibited the NaF‐induced generation of cGMP. These results suggest that NaF‐induced cGMP generation occurs via a calcium/calmodulin‐ and NOS‐dependent pathway. (b) The basal intracellular Ca 2+ concentration ([Ca 2+ ] i ) was transiently greater at 1 and 3 h after pretreatment with NaF. W‐7 and W‐13 antagonized the increase in [Ca 2+ ] i , whereas NMMA had little effect. This suggests that the NaF‐induced change in basal [Ca 2+ ] i was mediated by a calmodulin‐dependent pathway but was independent of a NOS‐sensitive pathway. (c) The serotonin (5‐HT)‐induced intracellular mobilization of Ca 2+ was reduced by pretreating the cells with NaF. The reduction in Ca 2+ mobilization was antagonized by genistein, a tyrosine kinase inhibitor. W‐7, W‐5, and H‐8 had no effect. Results suggest that NaF differentially regulates the cGMP generation, basal [Ca 2+ ] i , and 5‐HT 2A receptor function in C6 glioma cells.