Resveratrol Inhibits GABAC rho Receptor-Mediated Ion Currents Expressed in Xenopus Oocytes

Resveratrol is a phytoalexin found in grapes, red wine, and berries. Resveratrol has been known to have many beneficial health effects, such as anti-cancer, neuroprotective, anti-inflammatory, and life-prolonging effects. However, relatively little is known about the effects of resveratrol on the regulation of ligand-gated ion channels. We have previously reported that resveratrol regulates subsets of homomeric ligand-gated ion channels such as those of 5-HT3A receptors. The gamma-aminobutyric acidC (GABAC) receptor is mainly expressed in retinal bipolar cells and plays an important role in visual processing. In the present study, we examined the effects of resveratrol on the channel activity of homomeric GABAC receptor expressed in Xenopus oocytes injected with cRNA encoding human GABAC rho subunits. Our data show that the application of GABA elicits an inward peak current (IGABA) in oocytes that express the GABAC receptor. Resveratrol treatment had no effect on oocytes injected with H2O or with GABAC receptor cRNA. Co-treatment with resveratrol and GABA inhibited IGABA in oocytes with GABAC receptors. The inhibition of IGABA by resveratrol was in a reversible and concentration-dependent manner. The IC50 of resveratrol was 28.9+/-2.8 microM in oocytes expressing GABAC receptor. The inhibition of IGABA by resveratrol was in voltage-independent and non-competitive manner. These results indicate that resveratrol might regulate GABAC receptor expression and that this regulation might be one of the pharmacological actions of resveratrol on the nervous system.

Inhibitory Effects of Quercetin on Muscle-type of Nicotinic Acetylcholine Receptor-Mediated Ion Currents Expressed in Xenopus Oocytes

The flavonoid quercetin is a low molecular weight compound generally found in apple, gingko, tomato, onion and other red-colored fruits and vegetables. Like other flavonoids, quercetin has diverse pharmacological actions. However, relatively little is known about the influence of quercetin effects in the regulation of ligand-gated ion channels. Previously, we reported that quercetin regulates subsets of nicotinic acetylcholine receptors such as alpha3beta4, alpha7 and alpha9alpha10. Presently, we investigated the effects of quercetin on muscle-type of nicotinic acetylcholine receptor channel activity expressed in Xenopus oocytes after injection of cRNA encoding human fetal or adult muscle-type of nicotinic acetylcholine receptor subunits. Acetylcholine treatment elicited an inward peak current (IACh) in oocytes expressing both muscle-type of nicotinic acetylcholine receptors and co-treatment of quercetin with acetylcholine inhibited IACh. Pre-treatment of quercetin further inhibited IACh in oocytes expressing adult and fetal muscle-type nicotinic acetylcholine receptors. The inhibition of IACh by quercetin was reversible and concentration-dependent. The IC50 of quercetin was 18.9+/-1.2 microM in oocytes expressing adult muscle-type nicotinic acetylcholine receptor. The inhibition of IACh by quercetin was voltage-independent and non-competitive. These results indicate that quercetin might regulate human muscle-type nicotinic acetylcholine receptor channel activity and that quercetin-mediated regulation of muscle-type nicotinic acetylcholine receptor might be coupled to regulation of neuromuscular junction activity.

Quercetin Inhibits alpha3beta4 Nicotinic Acetylcholine Receptor-Mediated Ion Currents Expressed in Xenopus Oocytes

Quercetin mainly exists in the skin of colored fruits and vegetables as one of flavonoids. Recent studies show that quercetin, like other flavonoids, has diverse pharmacological actions. However, relatively little is known about quercetin effects in the regulations of ligand-gated ion channels. In the previous reports, we have shown that quercetin regulates subsets of homomeric ligand-gated ion channels such as glycine, 5-HT3A and alpha7 nicotinic acetylcholine receptors. In the present study, we examined quercetin effects on heteromeric neuronal alpha3beta4 nicotinic acetylcholine receptor channel activity expressed in Xenopus oocytes after injection of cRNA encoding bovine neuronal alpha3 and beta4 subunits. Treatment with acetylcholine elicited an inward peak current (IACh) in oocytes expressing alpha3beta4 nicotinic acetylcholine receptor. Co-treatment with quercetin and acetylcholine inhibited IACh in oocytes expressing alpha3beta4 nicotinic acetylcholine receptors. The inhibition of IACh by quercetin was reversible and concentration-dependent. The half-inhibitory concentration (IC50) of quercetin was 14.9+/-0.8 microM in oocytes expressing alpha3beta4 nicotinic acetylcholine receptor. The inhibition of IACh by quercetin was voltage-independent and non-competitive. These results indicate that quercetin might regulate alpha3beta4 nicotinic acetylcholine receptor and this regulation might be one of the pharmacological actions of quercetin in nervous systems.

Remifentanil increases the activity of the glutamate transporter, EAAC1, expressed in Xenopus oocytes

BACKGROUND: Remifentanil has gained wide clinical acceptance during anesthesia due to its short context-sensitive half time and organ-independent metabolism. However, its mechanism as an anesthetic remains unclear. Glutamate transporters may be important targets for anesthetic action in the central nervous system, and we tested whether remifentanil affected the activity of the primary neuronal glutamate transporter, EAAC1 (excitatory amino acid carrier 1). METHODS: EAAC1 was expressed in Xenopus oocytes by mRNA injection. By using two-electrode voltage clamping, membrane currents were recorded before, during, and after application of L-glutamate (30microM) in the presence or absence of remifentanil. Oocytes were exposed to a protein kinase C (PKC) activator and inhibitor to study the role of PKC on EAAC1 activity. RESULTS: L-Glutamate induced an inward current in EAAC1-expressing oocytes. This response increased in a bell-shaped manner in the presence of 0.1microM to 1 mM remifentanil. Remifentanil significantly increased Vmax (3.1 +/- 0.2microC for controls vs. 4.9 +/- 0.3 microC for remifentanil treatment; n = 12-15; P < 0.05). However, remifentanil did not significantly change Km. Treatment of the oocytes with phorbol-12-myristate-13-acetate (PMA), a PKC activator, caused a significant increase in transporter current (1.00 +/- 0.03 to 1.35 +/- 0.03microC; P < 0.05). Oocytes pretreated with the PKC inhibitor alone (staurosporine) abolished remifentanilenhanced EAAC1 activity. CONCLUSIONS: Our data suggests that remifentanil enhances EAAC1 activity and that PKC is involved in mediating this effect.

p21-Activated Kinase 2 Involved in Cytokinesis Independent of Cdc42 During Xenopus Oocyte Maturation / 生物化学与生物物理进展

p21-Activated kinases including p21-activated kinase 2 contributed to the regulation of actin cytoskeleton and cell dynamics. In order to investigate the function of PAK2 on the maturation of Xenopus oocyte, PAK2-NT(PAK2-N-terminal,PAK2-NT) and PAK2-NTm (PAK2-N-terminal mutation) mRNA were microinjected into Xenopus oocyte respectively. Under fluorescent microscopy germinal vesicle breakdown was observed during cytokinesis. To further observe the relationship of oocyte cytokinesis, polar body formation and Cdc42 activity, confocal microscopy with time-lapse was employed . As a result, occurrences of germinal vesicle breakdown in oocytes were similar to those oocytes injected with PAK2-NT mRNA or injected with PAK2-NTm mRNA,but no cytokinesis and polar body formation were observed in oocytes injected with PAK2-NT mRNA or PAK2-NTm mRNA. These results indicated that PAK2 involved in Xenopus oocytes cytokinesis and polar body formation independent of Cdc42 activity.

Block of ATP-sensitive K+ channels expressed in Xenopus oocytes by dimethyl sulfoxide

The effects of dimethyl sulfoxide (DMSO) were studied in two groups of Xenopus oocytes, one expressing ATP sensitive K+ (KATP) channel comprised of sulfonylurea receptor SUR1 and inwardly rectifying K+ channel subunit Kir6.2, and the other expressing renal KATP channel ROMK2. At concentrations of 0.3~10% (vol/vol) DMSO inhibited whole cell Kir6.2/SUR1 currents elicited by bath application of sodium azide (3 mM) in a concentration-dependent manner. The inhibition constant and Hill coefficient were 2.93% and 1.62, respectively. ROMK2 currents, however, was not affected significantly by DMSO. The results support the idea that DMSO inhibits KATP channel expressed in Xenopus oocyte through a protein-specific mechanism(s) that remains to be further elucidated.

Effect of ligustrazine on the human scavenger receptor-AI expressed in Xenopus oocytes / 中国药理学通报

Aim To investigate and evaluate the effect of ligustrazine on the expression of scavenger receptor type AI, the human ?-interferon activation site (GAS) elements regulatory systems of SR-AI expression wasfirst established in the Xenopus oocytes. Methods A plasmid, in which the human SR-AI gene was constructed downstream from the GAS elements, was microinjected into the nucleus of Xenopus oocytes. The oocytes then were cultured in the smooth muscle cell conditioned medium (SCM), In which the cell were cultured with the treatment of oxLDL for 2 days. In the other groups, the oocytes were treated with SCM containing the nature medicines ligustrazine, and the positive control drug ?-interferon respectively. Results The results demonstrated that SCM could upregulate the expression of SR-AI in this system, this action was suppressed by ligustrazine and ?-interferon. Conclusion Similar to the action of ?-interferon, ligustrazine can prevent the over-expression of SR-A induced by oxLDL, via their effect on the GAS elements regulatory pathway.