Influence of cellular incorporation of n-3 eicosapentaenoic acid on intracellular Ca2+ concentration and membrane potential in vascular smooth muscle cells.
Long-term treatment with n-3 eicosapentaenoic acid (EPA) has been shown to exert hypotensive effects and have beneficial effects on atherosclerosis. To elucidate one of the underlying mechanisms of these effects, intracellular calcium concentration [Ca2+]i, and resting membrane potential were measured in rat vascular smooth muscle cells (A7r5 cell) treated with EPA, using Ca2+-sensitive dye fura-2 AM and the patch clamp technique. The alterations in fatty acid compositions of phospholipids and cell migration after treatment with EPA (30 microM) for 6 h-7 days were also examined. After treating cells with EPA, the EPA and DPA (docosapentaenoic acid) content of the phospholipid fraction (mol.%) increased in a time-dependent manner. Alternatively, arachidonic acid (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 microM) for 7 days. Vasopressin (100 nM), endothelin-1 (100 nM) and platelet-derived growth factor (PDGF 5 ng/ml) evoked an initial peak of [Ca2+]i, followed by a smaller sustained rise of [Ca2+]i in the presence of extracellular Ca2+. In EPA-treated cells, both the peak and the sustained rise of [Ca2+]i induced by these agonists decreased in comparison to the control cells. EPA treatment also decreased the transient [Ca2+]i rise evoked by these agonists in the absence of extracellular Ca2+. Under the current clamp condition, resting membrane 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, P < 0.05), and the input resistance of the cell was lower in EPA-treated cells, while cell size and capacitance were not statistically different. In addition, long-term treatment with EPA for 7 days significantly inhibited PDGF-induced cell migration. These results suggest that cellular incorporation of n-3 eicosapentaenoic acid attenuates intracellular mechanisms related to changes of [Ca2+]i and affects membrane potential, thereby inhibiting migration of vascular smooth muscle cells. These actions of EPA may contribute to its vasorelaxant and antiatherosclerotic effects.
Asano
M
M
Second Department of Internal Medicine, Faculty of Medicine, University of Tokyo, Japan.
Nakajima
T
T
Hazama
H
H
Iwasawa
K
K
Tomaru
T
T
Omata
M
M
Soma
M
M
Asakura
Y
Y
Mizutani
M
M
Suzuki
S
S
Yamashita
K
K
Okuda
Y
Y
D000818:Animals; D001011:Aorta / Q000166:cytology / Q000378:metabolism / Q000502:physiology; D002118:Calcium / Q000378:metabolism*; D002465:Cell Movement / Q000187:drug effects; D015118:Eicosapentaenoic Acid / Q000378:metabolism*; D005227:Fatty Acids / Q000378:metabolism; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D007425:Intracellular Membranes / Q000378:metabolism*; D008564:Membrane Potentials / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D009994:Osmolar Concentration; D051381:Rats; D013997:Time Factors
D005227:Fatty Acids; D005231:Fatty Acids, Unsaturated; D015118:Eicosapentaenoic Acid; D002118:Calcium