Biphasic effects of sodium danshensu on vessel function in isolated rat aorta

Abstract

Aim: To investigate the effects of sodium danshensu on vessel function in isolated rat aortic ring.

Methods: Thoracic aortae from normal rats were isolated and equilibrated in organ bath with Krebs-Henseleit buffer and ring tension was recorded. Effects of sodium danshensu on basal tonus of the vessel and its effects on vessel contraction and relaxation with or without endothelium were observed.

Results: In thoracic arteries under basal tonus, sodium danshensu (0.3-3 g/L) produced a dose-dependent transient contraction. In phenylephrine-precontracted thoracic arteries with or without endothelium, low concentration (0.1-0.3 g/L) of sodium danshensu produced a weak contraction, while high concentrations (1-3 g/L) produced a pronounced vasodilator after a transient vasocontraction. Pre-incubation with sodium danshensu could inhibit vessel contraction induced by phenylephrine and potassium chloride in a concentration-dependent way. Sodium danshensu inhibited phenylephrine- and CaCl(2)-induced vasoconstriction in Ca(2+)-free medium. Pre-incubation with tetraethylammonium, a non-selective K(+) channel blocker, and apamin, a small-conductance calcium-activated K(+) channel blocker partially antagonized the relaxation response induced by sodium danshensu. However, iberiotoxin (big-conductance calcium-sensitive K(+) channel blocker), barium chloride (inward rectifier K(+) channel blocker), and glibencalmide (ATP-sensitive K(+) channel blocker) had no influence on the vasodilation effect of sodium danshensu.

Conclusion: Sodium danshensu showed a biphasic effects on vessel tension. While low dosage of sodium danshensu produced small contraction possibly through transient enhancement of Ca(2+) influx, high dosage produced significant vasodilation mainly through promoting the opening of non-selective K(+) channels and small-conductance calcium-sensitive K(+) channels in the vascular smooth muscle cells.

Figure 1

Chemical structure of sodium danshensu

Figure 2

Effect of sodium danshensu on basal tonus in normal Krebs-Henseleit buffer (A) and in Ca²⁺-free Krebs-Henseleit buffer containing 1 mmol/L ethyleneglycoltetraacetic acid (EGTA) (B).

Figure 3

Representative tracing of vessel contraction and relaxation at different concentrations (A) and dose- and time-dependent vasoactive effects of sodium danshensu in aortic rings with and without endothelium (B).

Figure 4

Effects of sodium danshensu on phenylephrine-induced contractile response in endothelium-denuded rat aortic rings. The responses were determined after 30-min pre-incubation with sodium danshensu. Data are mean±SD. n=6–7 segments.

Figure 5

Effects of sodium danshensu on KCl-induced contractile response in endothelium-denuded rat aortic rings. The responses were determined after 30-min pre-incubation with sodium danshensu. Data are mean±SD. n=6–7 segments.

Figure 6

Effects of sodium danshensu on CaCl₂-induced contractile response in endothelium-denuded rat aortic rings. Contraction induced by CaCl₂ was determined in Ca²⁺-free solution containing 30 mmol/L KCl after 30-min incubation with sodium danshensu (0.3, 1, and 3 g/L).

Figure 7

Effects of sodium danshensu on intracellular Ca²⁺ release sensitive to phenylephrine in aortic rings. Intracellular Ca²⁺ release sensitive to phenylephrine was examined by contraction the rings with phenylephrine after exposure for 1 min to calcium-free medium after 30-min incubation with sodium danshensu (0.3, 1, and 3 g/L).

Figure 8

Effects of different K⁺ channel blockers on sodium danshensu (3 g/L)-induced relaxation in 1 μmol/L phenylephrine-precontracted endothelium-denuded rat thoracic aortic rings. Each individual blocker was pre-incubated with the rat aorta for 10 min prior to stimulation with 1 μmol/L phenylephrine. Sodium danshensu (3 g/L) was added after the contraction to phenylephrine reached plateau. Non-selective K⁺ channel blocker tetraethylammonium (TEA, 10 mmol/L) and small-conductance Ca²⁺-activated K⁺ channel blocker apamin (0.1 μmol/L) significantly partially reduced sodium danshensu-induced relaxation, while big-conductance Ca²⁺-activated K⁺ channel blocker iberiotoxin (0.1 μmol/L), inward rectifier K⁺ channel blocker barium chloride (BaCl₂, 30 μmol/L) and ATP-sensitive K⁺ channel blocker glibencalmide (3 μmol/L) did not alter the relaxant effect of sodium danshensu. The combination of non-selective K⁺ channel blocker TEA (10 mmol/L) and small-conductance Ca²⁺-activated K⁺ channel blocker apamin (0.1 μmol/L) also produced significant inhibition partially, but not entirely. ^cP<0.01 vs control. ^fP<0.01 vs TEA 10 mmol/L.

Figure 9

Effect of sodium danshensu on the content of cGMP in rat thoracic aorta with endothelium. The content of cGMP in rat thoracic aorta with endothelium was significantly depressed after being incubated with sodium danshensu, in a dose-dependent manner. ^cP<0.01 vs control.