Contribution of L-type Ca2+ channel-sarcoplasmic reticulum coupling to depolarization-induced arterial contraction in spontaneously hypertensive rats

Vascular relaxing effect of Hydrocotyle umbellata L. is mediated by blocking of l-type Ca2+ channels

ETHNOPHARMACOLOGICAL RELEVANCE

Hydrocotyle umbellata L. is a medicinal herb for the treatment of some health problems including hypertension, according to traditional medicine. Even so, its vascular effects and the pharmacological action mechanisms have not been analyzed.

AIM OF THE STUDY

This experiment aimed to analyze the effects of hydroalcoholic extract of Hydrocotyle umbellata L. (HEHU) on isolated vessels and verify the interaction of hibalactone (chemical marker) against Ca_v1.2 channels using molecular docking.

MATERIALS AND METHODS

Vascular reactivity experiments were performed using rat aortas with (E⁺) or without endothelium (E^-) in an isolated organ bath. Computational molecular docking approaches were used to show the direct effect on L-type Ca²⁺ Channels.

RESULTS

HEHU (0-560 μg/mL) induced relaxation of the pre-contracted arteries in a concentration-dependent manner. The maximum effect was higher in E⁺ (76.8 ± 4.1%) as compared to E^- (47.3 ± 5.5%). Pre-treatment of E⁺ arteries with L-NAME or ODQ reduced the relaxation to similar level of E^- arteries. The treatment of arteries with MDL-12,330 A, diclofenac, propranolol and atropine did not change the relaxation induced by HEHU. The contraction caused by internal Ca²⁺ release induced by caffeine was reduced after HEHU treatment. Moreover, the HEHU also impaired the contraction induced by Ca²⁺ influx stimulated with phenylephrine or high KCl. The docking study demonstrated the effectiveness of hibalactone in blocking the Ca_v1.2 channel.

CONCLUSIONS

These findings show that HEHU induces vascular relaxation which is potentiated (but not dependent) by endothelial cells. Blocking of Ca²⁺ influx seems to be the main mechanism for the vascular effects of HEHU.

TMEM16A-encoded anoctamin 1 inhibition contributes to chrysin-induced coronary relaxation

BACKGROUND

Chrysin, a natural flavonoid available in honey, propolis and medicinal plants, has been shown to be vasorelaxant in some vascular beds. Proper intake of an alimental vasodilator as a food additive may be a promising strategy for prevention and treatment of coronary spasmodic disorders.

PURPOSE

TMEM16A-encoded anoctamin 1 (ANO1), a Ca²⁺ activated Cl^- channel (CaCC), plays an important role in the modulation of vascular tone. We tested the possibility that inhibition of CaCCs contributes to chrysin-induced coronary arterial relaxation.

METHODS

The vascular tone of the rat coronary artery (RCA) was recorded with a wire myograph. CaCC currents were assessed using whole-cell patch clamp in arterial smooth muscle cell (ASMC) freshly isolated from RCAs. An inhibitor study was performed to explore the mechanisms underlying the vasomotor and electrophysiological effects of chrysin.

RESULTS

Pre-incubation with chrysin depressed the contractions elicited by thromboxane A2 analog U46619, vasopressin (VP), depolarization and extracellular Ca²⁺ elevation/depolarization without significant preference among these vasoconstrictors. Besides, chrysin inhibited both intracellular Ca²⁺ release-dependent and extracellular Ca²⁺ influx-dependent components of contractions induced by U46619 or VP. In RCAs pre-contracted with U46619, VP or KCl, chrysin elicited concentration-dependent relaxations, which were weakened by Cl^- -deprivation. The electrophysiological study showed that chrysin reduced ANO1-antibody-sensitive CaCC currents and depressed CaCC increments induced by U46619. Inhibitor study showed that both the vasorelaxation and the CaCC current reduction induced by chrysin were attenuated by blocking CaCCs and inhibiting cAMP/PKA and NO/PKG pathways.

CONCLUSION

The present findings indicate that inhibition of RCA ASMC CaCC currents, which may be consequential following intracellular Ca²⁺ availability reduction and activation of cAMP/PKA and NO/cGMP signaling pathways, contributes to chrysin-induced RCA relaxation.