Differential effects of polychlorinated biphenyl congeners on phosphoinositide hydrolysis and protein kinase C translocation in rat cerebellar granule cells

Abstract

Previous reports from our laboratory have suggested that the neuroactivity of some polychlorinated biphenyl (PCB) congeners is associated with perturbations in cellular Ca 2+-homeostasis. We have characterized further the neurochemical effects of PCBs on signal transduction in primary cultures of cerebellar granule cells. The present experiments found that neither 2,2′-dichlorobiphenyl (DCBP), an ortho-substituted congener, nor 3,3′,4,4′,5-pentachlorobiphenyl (PCBP), a non- ortho-substituted congener, affected basal phosphoinositide (PI) hydrolysis in cerebellar granule cells. However, at concentrations up to 50 μM, DCBP potentiated carbachol-stimulated PI hydrolysis, while decreasing it at 100 μM. PCBP, on the other hand, had no effect on carbachol-stimulated PI hydrolysis in concentrations up to 100 μM. [ 3H]Phorbol ester ([ 3H]PDBu) binding was used to determine protein kinase C (PKC) translocation. DCBP increased [ 3H]PDBu binding in a concentration-dependent manner and a twofold increase was observed at 100 μM in cerebellar granule cells. PCBP had no effect on [ 3H]PDBu binding at concentrations up to 100 μM. The effect of DCBP on [ 3H]PDBu binding was time-dependent and was also dependent on the presence of external Ca 2+ in the medium. To test the hypothesis that DCBP increases [ 3H]PDBu binding by acting on receptor-activated calcium channels, the effects of DCBP were compared to those of l-glutamate. The effects of DCBP (50 μM) and glutamate (20 μM) were additive. MK-801, a non-competitive NMDA antagonist, blocked the effects of glutamate, but had no effect on the DCBP-induced increase in [ 3H]PDBu binding. Other pharmacological pretreatments such as incubations with 3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP; competitive NMDA antagonist), 6-cyano-7-nitro quinoxaline-2,3-dione (CNQX; AMPA antagonist), verapamil (Ca 2+-channel antagonist) or tetrodotoxin (Na + channel antagonist) also had no effect on DCBP-induced increased in [ 3H]PDBu binding. These studies indicate that DCBP, a putative neuroactive PCB congener, has a biphasic effect on receptor-mediated PI hydrolysis and causes translocation of PKC in cerebellar granule cells.