Endothelium-independent relaxant effect of rubus coreanus extracts in corpus cavernosum smooth muscle

摘要

Introduction: Rubus coreanus is a perennial shrub native to the southern part of the Korean peninsula. Although it is known that R.coreanus has a dose-dependent relaxation effect on rabbit corpus cavernosum (CC), the exact mechanism of action by which R.coreanus work is not fully known. Aims: To elucidate the direct effects of unripe R.coreanus extract (RCE) on CC smooth muscle cells. Methods: Dried unripe R.coreanus fruits were pulverized and extracted with 95% ethanol. Isolated rabbit CC strips were mounted in an organ-bath system, and the effects of RCE were evaluated. To estimate [Ca2+]i, we used a Fura-2 fluorescent technique. Main Outcome Measures: The effects of unripe RCE on ion channels and the intracellular Ca2+ concentration ([Ca2+]i) of CC. Results: RCE effectively relaxed phenylephrine (PE)-induced tone in rabbit CC, and removal of the endothelium did not completely abolish the relaxation effect of RCE. Tetraethylammonium (1mM) did not inhibit RCE-induced relaxation in strips precontracted by PE in the organ bath. However, CaCl2-induced constriction of CC strips, bathed in Ca2+-free buffer and primed with PE, was abolished by RCE. In addition, RCE decreased basal [Ca2+]i in corporal smooth muscle cells. The increases of [Ca2+]i evoked by 60mM K+-containing solution in A7r5 cells were suppressed by RCE, and RCE relaxed KCl-induced tone in endothelium-free CC, which indicated that RCE blocked the voltage-dependent Ca2+ channels (VDCCs). RCE decreased basal [Ca2+]i and the [Arg8]-vasopressin-induced [Ca2+]i increases in A7r5 cells, and RCE inhibited the contraction of endothelium-free CC induced by PE in Ca2+-free solution, which suggested that RCE might act as a modulator of corporal smooth muscle cell tone by inhibiting Ca2+ release from sarcoplasmic reticulum. Conclusion: RCE acts through endothelium-independent and endothelium-dependent pathways to relax CC. RCE may inhibit VDCCs and Ca2+ release from sarcoplasmic reticulum.