Abstract
Exposure in vitro to the mixture of polychlorinated biphenyls (PCBs), Aroclor 1242, stimulates superoxide anion (O2-) production and degranulation in rat polymorphonuclear neutrophils (PMNs). The mechanism by which PCBs activate PMNs is unknown. Phospholipase C-dependent hydrolysis of membrane phosphoinositides is an important early event in PMN activation in response to several agonists including N-formyl-methionyl-leucyl phenylalanine (fMLP); therefore, the present study was undertaken to determine whether Aroclor 1242 stimulates the production of inositol phosphates in isolated rat PMNs. PMNs elicited with glycogen from rat peritoneum were labeled with myo-[2-3H]inositol, and the effect of fMLP and Aroclor 1242 on accumulation of [3H]inositol phosphates was determined. Both fMLP (in the presence of cytochalasin B) and Aroclor 1242 induced rapid breakdown of inositol-containing phospholipids. Peak accumulation of [3H]inositol phosphates occurred within 5 sec in response to Aroclor 1242 and within 15-30 sec in response to fMLP. In cytochalasin B-treated PMNs, significant O2- generation occurred within 5 min of exposure to fMLP or Aroclor 1242. 2,2',4,4'-Tetrachlorobiphenyl (TCB), but not 3,3',4,4'-TCB, stimulates O2- production and degranulation in isolated rat PMNs. To determine whether inositol phosphate accumulation parallels PMN activation, [3H]inositol monophosphate (IP) production was measured in response to Aroclor 1242, 2,2'4,4'-TCB, and 3,3'4,4'-TCB in LiCl-treated cells. Both Aroclor 1242 and 2,2',4,4'-TCB, but not 3,3',4,4'-TCB, caused significant accumulation of [3H]IP. Previous reports indicate that cytochalasin B enhances PMN activation in response to fMLP by increasing the production of inositol phosphates. Pretreatment of PMNs with cytochalasin B significantly enhanced O2- production in cells exposed to Aroclor 1242 but did not alter [H]IP accumulation. These data suggest that treatment of rat PMNs with Aroclor 1242 stimulates PI turnover and are consistent with the hypothesis that hydrolysis of membrane phospholipids is important in PMN activation by PCBs. The enhancing effect of cytochalasin B on PCB-induced O2- production, however, likely involves other mechanisms.
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