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 μM 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.