| Summary: | 碩士 === 長庚大學 === 基礎醫學研究所 === 92 === Cl- is essential for vasoconstrictory responses; it enhances receptor activation-induced signaling including Ca2+ transients and gene expression. Since high Cl- diet-induced hypertension is associated with vascular wall thickening and mitogenic response of vascular smooth muscle is often mediated by phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2), we asked whether Cl- enhances cyclic mechanical strain-induced ERK1/2 phosphorylation in cultured vascular smooth muscle cells (VSMC). Cultured VSMC were obtained from the aorta of neonatal Sprague Dawley rats and were subjected to cyclic mechanical deformation (5-20% elongation; 1 Hz) with Flexcell Strain unit (FX-4000) after removal of serum for 24 hr. Cyclic strain (20%) induced a time-dependent increase in ERK1/2 phosphorylation in VSMC, which peaked at 10 min after initiation of strain, as measured by Western blot analysis. In VSMC, both 10 and 20% of cyclic strain induced an approximately 2-fold increase in DNA synthesis, as determined by [3H]-thymidine incorporation, which peaked 24 hr after initiation of cyclic strain and returned to basal level by 48 hr of strain. An antioxidant, N-acetylcysteine, and an inhibitor of epidermal growth factor receptor (EGFR), AG1478, significantly attenuated cyclic strain-induced ERK1/2 phosphorylation, suggesting a role of reactive oxygen species (ROS) and EGFR in modulating upstream signaling of ERK1/2 phosphorylation induced by cyclic strain in VSMC. After incubation of VSMC in physiological salt solutions with Cl- of 120 vs. 20 mEq/L for 45 min, cyclic strain-induced ERK1/2 phosphorylation was significantly reduced in low vs. high [Cl-]. Pretreatment of a catalase inhibitor, 3-AT, did not alter the level of ERK1/2 phosphorylation induced by cyclic strain, suggesting the effect of Cl- may not be mediated by catalase inhibition. Our results demonstrate a Cl--dependent ERK1/2 phosphorylation induced by cyclic mechanical strain in VSMC. Cl- may participate in vascular remodeling observed in salt-sensitive hypertension.
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