Intracellular free calcium concentration and thromboxane A₂ formation of vascular smooth muscle cells are influenced by fish oil and n-3 eicosapentaenoic acid

Abstract

The effect of fish oil and n-3 eicosapentaenoic acid (EPA) on intracellular free calcium concentration ([Ca²⁺]_i) and thromboxane B₂ (TXB₂) formation in resting and stimulated cultured rat vascular smooth muscle cells (VSMC) was examined. In resting control cells [Ca²⁺]_i was 147 ± 15 nmol l^-1 (mean ± SEM, n=4). After pretreatment of the cells with fish oil or EPA for 24 days the resting [Ca²⁺]_i was decreased to 126 ± 10 nmol l^-l and 84 ± 8 nmol^-1, respectively. After stimulation of untreated control cells with either 100 nmol 1^-1 angiotensin II (All), 40 μg ml^-1 low-density lipoprotein (LDL), or 100 ng ml^-1 of recombinant platelet-derived growth factor (PDGF_AB), [Ca²⁺]_i was (in nmol 1^-1) 306 ± 31, 217 ± 25 and 213 ± 16. Treatment of cells with fish oil or EPA reduced the stimulatory effect of the agonists, and the following [Ca²⁺]_i values (in nmol l^-1) were found: 199 ± 21, 131 ± 10, 148 ± 13; and 175 ± 11, 98 ± 12, and 103 ± 6, respectively. PDGF_AB induced a four fold increase in TXB₂-generation (270 ± 28 pg mg^-1 cell protein compared with 61 ± 8.2 pg mg^-1 in unstimulated control cells) within 6 min. In cells pretreated with fish oil or EPA, TXB₂-formation was reduced by 54% and 44%, respectively. In conclusion: in rat VSMC stimulated by a variety of vasoactive agonists, fish oil and EPA can markedly attenuate intracellular mechanisms related to changes of cytosolic calcium concentration and eicosanoid production. These findings might partly explain, on the subcellular level, the beneficial effects of fish oil on atherosclerosis and hypertension.

Key Words:

• cytosolic calcium
• fish oil
• rat aortic cells
• thromboxane A₂