INFLUENCE OF CELLULAR INCORPORATION OF N-3 EICOSAPENTAENOIC ACID ON INTRACELLULAR CA2-POTENTIAL IN VASCULAR SMOOTH-MUSCLE CELLS( CONCENTRATION AND MEMBRANE)

Long-term treatment with n-3 eicosapentaenoic acid (EPA) has been show n to exert hypotensive effects and have beneficial effects on atherosc lerosis. To elucidate one of the underlying mechanisms of these effect s, intracellular calcium concentration [Ca2+](i), and resting membrane potential were measured in rat vascular smooth muscle cells (A7r5 cel l) treated with EPA, using Ca2+-sensitive dye fura-2 AM and the patch clamp technique. The alterations in fatty acid compositions of phospho lipids and cell migration after treatment with EPA (30 mu M) for 6 h-7 days were also examined. After treating cells with EPA, the EPA and D PA (docosapentaenoic acid) content of the phospholipid fraction (mol.% ) increased in a time-dependent manner. Alternatively, arachidonic aci d (AA) decreased, and then the ratio of EPA and AA (EPA/AA) increased significantly. The resting [Ca2+](i) decreased from 170 +/- 46 nM (n = 16) in control cells to 123 +/- 29 nM (n = 16) in cells treated with EPA (30 mu M) for 7 days. Vasopressin (100 nM), endothelin-l (100 nM) and platelet-derived growth factor (PDGF 5 ng/ml) evoked an initial pe ak of [Ca2+](i), followed by a smaller sustained rise of [Ca2+](i) in the presence of extracellular Ca2+. In EPA-treated cells, both the pea k and the sustained rise of [Ca2+](i) induced by these agonists decrea sed in comparison to the control cells. EPA treatment also decreased t he transient [Ca2+](i), rise evoked by these agonists in the absence o f extracellular Ca2+. Under the current clamp condition, resting membr ane potential was significantly higher in EPA-treated cells (-49.8 +/- 10.4 mV, n = 41) than in control cells (-44.6 +/- 7.4 mV, n = 41, Pt 0.05), and the input resistance of the cell was lower in EPA-treated c ells, while cell size and capacitance were not statistically different . In addition, long-term treatment with EPA for 7 days significantly i nhibited PDGF-induced cell migration. These results suggest that cellu lar incorporation of n-3 eicosapentaenoic acid attenuates intracellula r mechanisms related to changes of [Ca2+](i) and affects membrane pote ntial, thereby inhibiting migration of vascular smooth muscle cells. T hese actions of EPA may contribute to its vasorelaxant and antiatheros clerotic effects. (C) 1998 Elsevier Science Ireland Ltd. All rights re served.