1 Mice lacking the apolipoprotein E and low density lipoprotein receptor genes (E8xLDLR8) develop atherosclerosis and endothelial dysfunction. The aim of this study was to characterize the roles of L-arginine and tetrahydrobiopterin (BH 4 ) for endothelium-dependent relaxation and the changes in the vasoconstrictor response to endothelin-1 (ET-1) in thoracic aortic rings of E8xLDLR8 mice. 2 Histological examination revealed severe atherosclerosis of the thoracic aorta of E8xLDLR8 mice. Relaxations induced by acetylcholine (Ach), but not that to sodium nitroprusside, were signi®cantly impaired in E8xLDLR8 mice compared to control mice indicating attenuated endothelium-dependent relaxations. 3 Preincubation with the nitric oxide (NO) substrate L-arginine did not a ect, whereas the cofactor for NO synthase, BH 4 , slightly improved the relaxations induced by Ach. Combined preincubation with L-arginine and BH 4 induced a pronounced enhancement of Ach-induced relaxations in E8xLDLR8 mice. The relaxations induced by Ach in E8xLDLR8 mice in the presence of L-arginine and BH 4 were not di erent from those observed in control mice. 4 Preincubation with superoxide dismutase did not a ect Ach-induced relaxations in aorta from E8xLDLR8 mice. 5 The contractile response to ET-1 was enhanced in E8xLDLR8 mouse aorta. The contractions were abolished by the ET A receptor antagonist LU 135252. The ET B receptor agonist sarafotoxin 6c did not induce contractions or relaxations. 6 It is concluded that endothelial dysfunction of E8xLDLR8 mouse aorta is reversed by combined administration of L-arginine and BH 4 . In addition, the ET A receptor-mediated vasoconstriction by ET-1 is enhanced in E8xLDLR8 mice.

1 Mice lacking the apolipoprotein E and low density lipoprotein receptor genes (E86LDLR8) develop atherosclerosis. The aim of this study was to investigate changes in endothelium-dependent vasodilation and vasomotion in thoracic aortic rings of E86LDLR8 mice. 2 K + -induced contractions of the aorta from E86LDLR8 mice were stronger than those from control mice. The sensitivity of E86LDLR8 aorta to phenylephrine (PE) was decreased but the maximal contractions were increased. Acetylcholine-induced, but not sodium nitroprusside-induced, relaxations of E86LDLR8 aorta was decreased. 3 PE induced rhythmic activity in both E86LDLR8 and control aorta but the amplitude was larger in E86LDLR8 than in control mice. PE-induced rhythmic activity in both E86LDLR8 and control aorta was augmented by increase in extracellular Ca 2+ -concentration, but was abolished by removal of the endothelium, the nitric oxide (NO) synthase inhibitor N-nitro-L-arginine methyl ester, the guanylate cyclase inhibitor LY-83583, high K + solution and ryanodine. 4 4-Aminopyridine, a voltage-dependent potassium (K V ) channel blocker, increased basal tension and induced rhythmic activity in E86LDLR8 aorta but not in control aorta. 5 The Ca 2+ -activated potassium (K Ca ) channel blockers tetraethylammonium and charybdotoxin abolished PE-induced rhythmic activity in E86LDLR8 aorta. 6 In conclusion, opening of K v channels in E86LDLR8 mice aorta is reduced and it is susceptible to be depolarized resulting in Ca 2+ entry. The vascular smooth muscle is then dependent on compensatory mechanisms to limit Ca 2+ -entry. Such mechanisms may be decreased sensitivity to vasoconstrictors, or increased opening of K Ca channels by NO via a cyclic GMP-dependent mechanism.

Aim: To explore the action of doxorubicin on vascular smooth muscle cells. Methods: Isometric tension of denuded or intact thoracic aortic vessels was recorded and [Ca 2+ ] i in isolated aortic smooth muscle cells was measured by using Fluo-3. Results: Doxorubicin induced phasic and tonic contractions in denuded vessels and increased levels of [Ca 2+ ] i in single muscle cells. Treatment with 10 µmol/L ryanodine had no effect on basal tension, but it did abolish doxorubicin-induced phasic contraction. Treatment with 10 mmol/L caffeine induced a transient phasic contraction only, and the effect was not significantly altered by ryanodine, the omission of extracellular Ca 2+ or both. Phenylephrine induced rhythmic contraction (RC) in intact vessels. Treatment with 100 µmol/L doxorubicin enhanced RC amplitude, but 1 mmol/L doxorubicin abolished RC, with an increase in maximal tension. Caffeine at 100 µmol/L increased the frequency of the RC only. In the presence of 100 µmol/L caffeine, however, 100 µmol/L doxorubicin abolished the RC and decreased its maximal tension. Treatment with 10 µmol/L ryanodine abolished the RC, with an increase in the maximal tension. In Ca 2+ -free solution, doxorubicin induced a transient [Ca 2+ ] i increase that could be abolished by ryanodine pretreatment in single muscle cells. The doxorubicin-induced increase in [Ca 2+ ] i was suppressed by nifedipine and potentiated by ryanodine and charybdotoxin. Conclusion: Doxorubicin not only releases Ca 2+ from the sarcoplasmic reticulum but also promotes the entry of extracellular Ca 2+ into vascular smooth muscle cells.

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