Differential Suppressions of Phospholipase C Isozymes in H2O2-Induced Oxidative Stress of Rat Aortic Smooth Muscle Cells

Abstract

Intracellular calcium ions([Ca2+]i) have an important function in modulating the contractility of all kinds of muscle, including vascular smooth muscle cells. Reactive oxygen species(ROS) can induce Ca2+-overload by directly affecting the Ca2+ handling proteins. Little is known that phospholipase C(PLC) isozymes are involved in the Ca2+-overload induced by ROS in smooth muscle cells. [Ca2+]i response to exogenous H2O2 or ionopore A23187 was measured using the fluorescent probe, fura2-AM, in rat aortic smooth muscle cells(RASMCs). The differential expression levels of PLC isozymes were measured in cells exposed actually with H2O2 or ionopore. The subsequent signaling cascades related with PLC isozymes were also investigated in RASMCs. H2O2(1 mM) inhibited the proliferation of RASMCs in DMEM containing 0.1% FBS and increased the [Ca2+]i by a 50%. In H2O2-stimulated RASMCs, the expression of PLC-δ1 was suppressed within 1 hr, but the other PLC isozymes, β-, and γ-form were not affected. In contrast, the expression of PLC-δ1 and PLC-γ1 were suppressed by ionophore, A23187 (10 mM), for 3 hrs. The activity of protein kinase C(PKC) was also suppressed in same trend of PLC-δ1, not PLC-γ1. In conclusion, the H2O2-induced Ca2+ overload may differentially suppress the expression of PLC isozymes in RASMCs and the decreased expression of PLC-δ1 subsequently inhibited the PKC activity. These results suggest that the PLC/ PKC-regulated Ca2+homeostasis is the crucial targets of exogenous ROS in H2O2-stimulated RASMC.