1998 Volume 36 Issue 3 Pages 258-262
Silica may act as a stimulator of pulmonary inflammation and fibrosis. The effect of silica on phospholipase D (PLD) activity assayed as accumulation of [3H] phosphatidylethanol ([3H]PtdEt) was examined in[3H]palmitic acid-labeled primary cultures of rat alveolar macrophages. Silica induced a rapid accumulation of[3H]PtdEt in a time (0, 15, 30 and 45min)-and concentration (0.5, 1.0, 2.5 and 5.0mg/ml)-dependent manner indicating PLD activation. This silica-stimulated PLD activity was attenuated by the pretreament with calcium chelator ethylene glycol-bis(β-aminoethyl ether) N, N, N', N'-tetraacetic acid (EGTA) or/and 1, 2-bis(2-aminophenoxy)ethane-N, N, N, N-tetraacetic acid acetoxymethyl ester (BAPTA/AM) (EGTA: 54.3±8.6%, BAPTA/AM: 67.5 ±7.8% and EGTA+BAPTA/AM: 35.8±2.9, respectively). Also, silica-induced PLD activation was partially inhibited by the pretreatment with nonspecific phospholipase C (PLC) and PLD inhibitor (neomycin; 66.4±4.8%) or specific PLC inhibitor (U73122; 70.8±4.6%). Sphingosine as a protein kinase C (PKC) inhibitor did not change silica-induced PLD activity indicating that PKC might not play a role in PLD activation by silica. Based on these results, we concluded that a silica-stimulated phospholipase D activity is present in the rat alveolar macrophages and is predominantly regulated by PLC-mediated intracellular calcium.
