Lipopolysaccharide regulates both serotonin- and thrombin-induced intracellular calcium mobilization in rat C6 glioma cells: Possible involvement of nitric oxide synthase-mediated pathway

To investigate the mechanisms by which lipopolysaccharide (LPS) affects Ca2+ signaling systems, we studied the effects of LPS on the serotonin (5‐HT)‐ or thrombin‐induced intracellular Ca2+ ([Ca2+]i) increase in rat C6 glioma cells. Pretreatment of the cells with 1 μg/ml LPS for 24 hr significantly inhibited [Ca2+]i increase induced by 10 μM 5‐HT‐ or 0.5 U/ml thrombin. Its inhibitory effects were both dose‐ and time‐dependent. Treatment with 1 mM dibutyryl cGMP (dbcGMP) for 30 min also significantly inhibited the 5‐HT‐ and thrombin‐induced [Ca2+]i increase to approximately 60–70% of control. However, simultaneous pretreatment with LPS and dbcGMP did not show any synergistic inhibition. The simultaneous pretreatment with LPS and the potent cGMP‐dependent protein kinase (PKG) inhibitors H‐8 and KT5823 for 24 hr significantly antagonized the inhibitory effect of LPS. Pretreatment of the cells with 1 μg/ml LPS for 24 hr significantly enhanced cGMP accumulation, while dexamethasone and NMMA (NOS inhibitors) significantly attenuated the LPS‐induced enhancement in cGMP accumulation. In addition, pretreatment of the cells with 100 nM dexamethasone for 24 hr significantly suppressed LPS‐induced inducible nitric oxide synthase (iNOS; type II NOS, NOS‐II) protein expression. These results indicate that LPS may inhibit both 5‐HT‐ and thrombin‐induced [Ca2+]i increase via iNOS expression and PKG activation pathway in rat C6 glioma cells. J. Neurosci. Res. 51:517–525, 1998. © 1998 Wiley‐Liss, Inc.