Antagonism of Ca²⁺ influx via L-type Ca²⁺ channels mediates the vasorelaxant effect of catharanthus roseus-derived vindorosine in rat renal artery

Catharanthus roseus is a traditional herbal medicine used in Asian and African countries for the treatment of various diseases including hypertension. The present study examined possible cellular mechanisms for the relaxation of rat renal arteries induced by vindorosine extracted from C. roseus. Intrarenal arteries were isolated from 200-300 g male Sprague-Dawley rats and treated with different pharmacological blockers and inhibitors for the measurement of vascular reactivity on a Multi Myograph System. Fluorescence imaging by laser scanning confocal microscopy was utilized to determine the intracellular Ca²⁺ level in the vascular smooth muscles of the renal arteries. Vindorosine in micromolar concentrations relaxes renal arteries precontracted by KCl, phenylephrine, 11-dideoxy-9α,11α-epoxymethanoprostaglandin F2α, and serotonin. Vindorosine-induced relaxations were unaffected by endothelium denudation or by treatment with the nitric oxide synthase inhibitor N ^G-nitro-L-arginine methyl ester hydrochloride, the guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, the cyclooxygenase inhibitor indomethacin, or K⁺ channel blockers such as tetraethylammonium ions, glibenclamide, and BaCl₂. Vindorosine-induced relaxations were attenuated in the presence of 0.1 μM nifedipine (an L-type Ca²⁺ channel blocker). Vindorosine also concentration-dependently suppressed contractions induced by CaCl₂ (0.01-5 mM) in Ca-free 60 mM KCl solution. Furthermore, fluorescence imaging using fluo-4 demonstrated that 30 min incubation with 100 μM vindorosine reduced the 60 mM KCl-stimulated Ca²⁺ influx in the smooth muscles of rat renal arteries. The present study is probably the first report of blood vessel relaxation by vindorosine and the possible underlying mechanisms involving the inhibition of Ca²⁺ entry via L-type Ca²⁺ channels in vascular smooth muscles.