Abstract
Proanthocyanidin is a phenolic compound present in plants, that has antioxidant, antinociceptive, anti-emetic, and neuroprotective properties. We investigated the actions of proanthocyanidin from grape seeds on 5-hydroxytryptamine (5-HT)3 receptors in NCB-20 neuroblastoma cells using a whole-cell voltage clamp technique. Co-treatment of proanthocyanidin (0.3—100 μg/ml) and 3 μM 5-HT (near EC50) produced a slight inhibition of 5-HT-induced inward peak current (I5-HT) in NCB-20 cells, but pretreatment with proanthocyanidin for 30 s before application of 5-HT induced a much larger inhibition of I5-HT in an irreversible, concentration- and time-dependent manner (IC50=6.5±0.4 μg/ml, Hill coefficient=2.5±0.1). Proanthocyanidin also produced a concentration-dependent inhibition of currents induced by 30 μM 5-HT, near-maximal concentration (IC50=22.1±0.4 μg/ml, Hill coefficient=2.4±0.1). High concentrations (≧30 μg/ml) of proanthocyanidin caused a concentration-dependent inhibition of the activation and desensitization of currents induced by 30 μM 5-HT. Further studies showed that pretreatment of 20 μg/ml proanthocyanidin caused not only a rightward shift of the dose–response curve for 5-HT (EC50 shift from 2.7±0.4 to 6.2±0.5 μM), but also a decreased Emax (inhibition by 37.5±1.3%). The proanthocyanidin-induced inhibition of 5-HT3 receptors did not show a significant difference within the testing holding potential ranges (−50—+30 mV). These results suggest that proanthocyanidin inhibits 5-HT3 receptor function in NCB-20 cells in a noncompetitive mode, and that this inhibitory effect of proanthocyanidin probably contributes to the pharmacological actions of proanthocyanidin.
