OBJECTIVE: To study hesperetin-induced vasorelaxation after depolarizing contraction in human umbilical veins (HUVs) to elucidate the role of L-type Ca²⁺ channel (LTCC) and related signaling pathway. METHODS: Isometric tension recording was performed in HUV rings pre-contracted with K⁺. Hesperetin relaxing mechanism was investigated using a LTCC opener (BayK8644) and blockers of cyclic nucleotides and phosphodiesterases (PDEs). Whole-cell patch-clamping in A7r5 cells, a rat vascular smooth muscle cell line, was performed to study the effect of hesperetin on LTCC current. RESULTS: After depolarizing precontraction, hesperetin induced HUV relaxation concentration-dependently and endothelium-independently; 1 mmol/L hesperetin reduced denuded HUV ring tension by 68.7% ± 4.3% compared to matching vehicle, osmolality, and time controls (P<0.0001). Importantly, hesperetin competitively inhibited BayK8644-induced contraction, shifting the half maximal effective concentration of BayK8644 response from 1.08 nmol/L [95% confidence interval (CI) 0.49-2.40] in vehicle control to 11.30 nmol/L (95% CI 5.45-23.41) in hesperetin (P=0.0001). Moreover, hesperetin elicited further vasorelaxation in denuded HUV rings pretreated with inhibitors of soluble guanylyl cyclase, adenylyl cyclase, PDE3, PDE4, and PDE5 (P<0.01), while rings pretreated with PDE1 inhibitors could not be relaxed by hesperetin (P>0.05). However, simultaneously applying inhibitors of soluble guanylyl cyclase and adenylyl cyclase could not inhibit hesperetin's effect (P>0.05). In whole-cell patch-clamping, hesperetin rapidly decreased LTCC current in A7r5 cells to 66.7% ± 5.8% (P=0.0104). CONCLUSIONS Hesperetin diminishes depolarizing contraction of human vascular smooth muscle through inhibition of LTCC, and not cyclic nucleotides nor PDEs. Our evidence supports direct LTCC interaction and provides additional basis for the use of hesperetin and its precursor hesperidin as vasodilators and may lead to future vasodilator drug development as a treatment alternative for cardiovascular diseases.
Hesperidin/pharmacology* ; Humans ; Calcium Channels, L-Type/metabolism* ; Umbilical Veins/physiology* ; Muscle Contraction/drug effects* ; Animals ; Rats ; Calcium Channel Blockers/pharmacology* ; Vasodilation/drug effects* ; Muscle Relaxation/drug effects*

OBJECTIVE: To investigate the effect of ferulic acid, a natural compound, on pancreatic beta cell viability, Ca²⁺ channels, and insulin secretion. METHODS: We studied the effects of ferulic acid on rat insulinoma cell line viability using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide viability assay. The whole-cell patch-clamp technique and enzyme-linked immunosorbent assay were also used to examine the action of ferulic acid on Ca²⁺ channels and insulin secretion, respectively. RESULTS: Ferulic acid did not affect cell viability during exposures up to 72 h. The electrophysiological study demonstrated that ferulic acid rapidly and concentration-dependently increased L-type Ca²⁺ channel current, shifting its activation curve in the hyperpolarizing direction with a decreased slope factor, while the voltage dependence of inactivation was not affected. On the other hand, ferulic acid have no effect on T-type Ca²⁺ channels. Furthermore, ferulic acid significantly increased insulin secretion, an effect inhibited by nifedipine and Ca²⁺-free extracellular fluid, confirming that ferulic acid-induced insulin secretion in these cells was mediated by augmenting Ca²⁺ influx through L-type Ca²⁺ channel. Our data also suggest that this may be a direct, nongenomic action. CONCLUSION This is the first electrophysiological demonstration that acute ferulic acid treatment could increase L-type Ca²⁺ channel current in pancreatic β cells by enhancing its voltage dependence of activation, leading to insulin secretion.
Rats ; Animals ; Insulin Secretion ; Insulin/pharmacology* ; Insulin-Secreting Cells/metabolism* ; Coumaric Acids/metabolism* ; Calcium/metabolism*