Mechanisms Underlying the Inhibition of Soman on NMDA-stimulated [ 3H]Norepinephrine Release from Rat Cortical Slices, Role of Phospholipase C and Protein Kinase C

Our previous studies indicated that soman inhibits N-methyl- d-aspartate (NMDA)-stimulated [ 3H]norepinephrine (NE) release from rat cortical slices by acting at a non-cholinergic site. In order to characterize the mechanisms, neomycin, a phospholipase C (PLC) inhibitor, and polymyxin B (PMB), a rather selective protein kinase C (PKC) inhibitor, were used to examine a possible involvement of PLC and PKC in the inhibitory effect of soman on NMDA-stimulated [ 3H]NE release. The role of pertussis toxin (PTX)-sensitive G-protein was also investigated by application of PTX. Neomycin (0.03–1.0 m m) inhibited the release in a concentration-dependent manner, which was inhibited by 1.0 m m soman. However, no significant interaction between soman and neomycin was observed. In addition, PMB (1.0 μg/ml) significantly inhibited release by 15.8%. With the presence of 1.0 m m soman, inhibition of release decreased from 29% (without PMB) to 5% (1.0 μg/ml PMB). Furthermore, both in the presence and absence of 1.0 m m soman, no significant differences for [ 3H]NE release were found between PTX (1.0 μg/ml)-treated and non-treated slices. These results suggest that the mechanism of the inhibitory effect of soman on NMDA-stimulated [ 3H]NE release in cortical slices appear to involve the effect on PKC, but not PLC and PTX-sensitive G-protein.