Effects of Schisandra chinensis extract on the contractility of corpus cavernosal smooth muscle (CSM) and Ca ²⁺ homeostasis in CSM cells

OBJECTIVE: • To evaluate the relaxant effects of Schisandra chinensis extract (SCE) on corporal tissue in the penis and to investigate the mechanism of action of SCE and its constituents on corporal smooth muscle (CSM) cells. MATERIALS AND METHODS: • The fruit of SC was collected and extracted with ethanol. Six SC lignans (schisandrol A, schisandrol B, schisandrin A, schisandrin B, gomisin N, and schisandrin C) were isolated and purified, and the chemical structures were confirmed by ¹H-nuclear magnetic resonance (NMR) and ¹³C-NMR data. • Isolated rabbit CSM strips were mounted in an organ-bath system, and the effects of SCE were evaluated. • To estimate the intracellular Ca ²⁺ level ([Ca ²⁺] i), we used a Fura-2 fluorescent technique, and a conventional whole-cell patch-clamp technique was used to measure the calcium-sensitive K ⁺channels (K _Ca), inward rectifier K ⁺ channels (K _IR), and canonical transient receptor potential cation channel 6 (TRPC6) currents. RESULTS: • SCE induced concentration-dependent relaxation in contracted CSM tissue, and the removal of the endothelium did not significantly affect their relaxation potencies. • In CSM cells, extracellular application of SCE significantly increased whole-cell K _Cacurrents (117.4%) and K _IR currents (110.0%). These effects were completely abolished by charybdotoxin or BaCl ₂. • In contrast, carbachol-induced TRPC6 channel activity was significantly inhibited (87.3%) by SCE in green fluorescent protein-TRPC6 pcDNA transfected HEK 293 cells. [Ca ²⁺]i measurements showed that SCE effectively reduced basal [Ca ²⁺]i in both cell lines (CSM cells and A7r5 cells) and the [Arg8]-vasopressin (AVP)-induced [Ca ²⁺]i increase in A7r5 cells. • Among the six SC lignans, schisandrin A and schisandrin B most effectively attenuated the AVP-induced [Ca ²⁺]i increase. CONCLUSIONS: • SCE induced relaxation of CSM that occurred primarily via an endothelium-independent pathway. • The relaxation effects of SCE on CSM were, in part, due to the activation of K ⁺channels and inhibition of TRPC6 channels, resulting in decreased [Ca ²⁺]i.