[Effects of isovitexin on transient outward potassium current of ventricular myocytes in rats].

To investigate the effects of isovitexin Ⅳ on transient outward potassium current in rat ventricular myocytes. In this study, MTT assay was used to investigate the safe range of isovitexin. The results showed that the IC50 of the drug was in the range of 10-30 µmol•L⁻¹, and the drug concentration of 1-3 µmol•L⁻¹ for the patch clamp test was within the safe range. In addition, the single ventricular myocytes were obtained by single-enzymatic hydrolysis through aortic retrograde perfusion. The transient outward potassium current (Ito) of rat ventricular myocytes was guided and measured by whole-cell patch-clamp technique and the changes of current characteristics were recorded after isovite was applied. When the concentration of IV was less than 0.1 µmol•L⁻¹, there was no significant effect on Ito. However, with the increase in the concentration of IV (≥0.3 µmol•L⁻¹), the peak of Ito was decreased gradually, from (32.32±2.9) pA/pF to （25.83±4.3） pA/pF, 1 µmol•L⁻¹ IV and (19.51±3.5) pA/pF, 3 µmol•L⁻¹ IV respectively, with an inhibition effect in a concentration-dependent manner. In the range of 1-3 µmol•L⁻¹, IV down-regulated the I-V curve of Ito significantly. The activation curve showed that IV can enable the maximum half activation potential (V1/2) to move to the positive direction, and the V1/2 was increased from (19.59±1.6) mV to (22.81±1.7) mV and (28.86±1.4) mV at concentration of 1, 3 µmol•L⁻¹, meanwhile the activation curve moved to the right. However, the maximum half inactivating potential (V1/2) of the steady-state inactivation curve of Ito was significantly decreased from (－51.43±0.99) mV to (－61.81±1.3) mV with concentration of 1 µmol•L⁻¹ and (－71.50±1.4) mV with concentration of 3 µmol•L⁻¹. The inactivation time constant of recovery from inactivation (τ) was up-regulated significantly from (94.89±0.73) ms to (118.5±1.5) ms and (162.4±1.4) ms at concentration of 1, 3 µmol•L⁻¹ respectively. Meanwhile IV could enable the inactivation recovery curve to move to the right, which suggested that it can prolong the recovery time from inactivation of the transient outward potassium channel. In conclusion, isovitexin had a high inhibitory effect on Ito in rat ventricular myocytes.

ZHX2 enhances the cytotoxicity of chemotherapeutic drugs in liver tumor cells by repressing MDR1 via interfering with NF-YA.

We previously reported the tumor suppressor function of Zinc-fingers and homeoboxes 2 (ZHX2) in hepatocellular carcinoma (HCC). Other studies indicate the association of increased ZHX2 expression with improved response to high dose chemotherapy in multiple myeloma. Here, we aim to test whether increased ZHX2 levels in HCC cells repress multidrug resistance 1(MDR1) expression resulting in increased sensitivity to chemotherapeutic drugs. We showed evidence that increased ZHX2 levels correlated with reduced MDR1 expression and enhanced the cytotoxicity of CDDP and ADM in different HCC cell lines. Consistently, elevated ZHX2 significantly reduced ADM efflux in HepG2 cells and greatly increased the CDDP-mediated suppression of liver tumor growth in vivo. Furthermore, immunohistochemical staining demonstrated the inverse correlation of ZHX2 and MDR1 expression in HCC tissues. Luciferase report assay showed that ZHX2 repressed the MDR1 promoter activity, while knockdown of NF-YA or mutating the NF-Y binding site eliminated this ZHX2-mediated repression of MDR1 transcription. Co-IP and ChIP assay further suggested that ZHX2 interacted with NF-YA and reduced NF-Y binding to the MDR1 promoter. Taken together, we clarify that ZHX2 represses NF-Y-mediated activation of MDR1 transcription and, in doing so, enhances the effects of chemotherapeutics in HCC cells both in vitro and in vivo.

[Effects of Forsythiae Fructus on guinea pig ileum contractility in vitro].

OBJECTIVE: To study contractility of guinea pig ileum in vitro,and analyze the mechanism of anti-emetic effects of Lianqiao. METHOD: Using emesis-relating agonists as drugs, the inhibitory effects of Lianqiao on guinea pig ileum contractility in vitro were observed in organ bath. RESULT: Lianqiao could inhibit guinea pig ileum spontaneous contractions, reducing the tone of contractions dose-dependently. Acetylcholine (Ach), histamine (His), 5-hydroxytryptamine (5-HT) stimulated contractions of the guinea pig ileum, enhanced the tone and amplitude. All the three doses (10, 5, 2 g x L(-1)) of Lianqiao could suppress the contractility, significantly reduced the tone and amplitude of ileum contractions stimulated by drugs but not the frequency. Dopamine could inhibit the spontaneous contraction tone and amplitude of ileum; Both the large doses (10, 5 g x L(-1)) of Lianqiao could antagonise the inhibitory effect of DA, enhance the tone and amplitude. Small dose(2 g x L(-1)) had additive effects on tone of ileum contractions with DA,but enhanced the amplitude not the frequency. CONCLUSION: Lianqiao have an inhibitory effect on guinea pig ileum contractions,the mechanism might be blocking M receptor, H1 receptor, 5-HT receptor and D2 receptor or directly suppressed ileum smooth muscle. The mechanisms of anti-emetic effect of Lianqiao needs further study.