Tea catechin, (-)-epigallocatechin gallate, causes membrane depolarizations of myenteric neurons in the guinea-pig small intestine

Suppression of the Excitability of Rat Nociceptive Secondary Sensory Neurons following Local Administration of the Phytochemical, (-)-Epigallocatechin-3-gallate

The phytochemical, polyphenolic compound, (-)-epigallocatechin-3-gallate (EGCG), is the main catechin found in green tea. Although a modulatory effect of EGCG on voltage-gated sodium and potassium channels has been reported in excitable tissues, the in vivo effect of EGCG on the excitability of nociceptive sensory neurons remains to be determined. Our aim was to investigate whether local administration of EGCG to rats attenuates the excitability of nociceptive spinal trigeminal nucleus caudalis (SpVc) neurons in response to mechanical stimulation in vivo. Extracellular single unit recordings were made from SpVc neurons in response to orofacial mechanical stimulation of anesthetized rats. The mean firing frequency of SpVc wide-dynamic range neurons following both non-noxious and noxious mechanical stimuli was significantly inhibited by EGCG in a dose-dependent and reversible manner. The mean magnitude of inhibition by EGCG on SpVc neuronal discharge frequency was similar to that of the local anesthetic, 1% lidocaine. Local injection of half-dose of lidocaine replaced the half-dose of EGCG. These results suggest that local injection of EGCG suppresses the excitability of nociceptive SpVc neurons, possibly via the inhibition of voltage-gated sodium channels and opening of voltage-gated potassium channels in the trigeminal ganglion. Therefore, administration of EGCG as a local anesthetic may provide relief from trigeminal nociceptive pain without side effects.

Non-classic androgen actions in Sertoli cell membrane in whole seminiferous tubules: effects of nandrolone decanoate and catechin

Studies show a mechanism of action of testosterone, nandrolone and catechin as agonists of the membrane androgen receptor. The aim of this work is to investigate the non-classical effect of androgens and catechin in Sertoli cells from immature rats. The membrane potential of Sertoli cells in whole seminiferous tubules was recorded using a standard single microelectrode technique. It was performed a topical application of testosterone (1 μM), nandrolone (0.1, 0.5 and 1 μM) and the flavonoid catechin (0.1, 0.5 and 1 μM) alone and also after infusion with flutamide (1 μM), diazoxide (100 μM) or U73122 (1 μM). The immature testes were incubated for 5 min in KRb with (45)Ca(2+), with or without nandrolone (1 μM). The results were given as mean±SEM. The data were analyzed using ANOVA for repeated measures with Bonferroni post-test. Testosterone produces a depolarization in the membrane potential at 120 s after application. Catechin (1 μM) and nandrolone (1 μM) have shown a similar response to testosterone: depolarization at 120 s after the application. The same response of catechin and nandrolone was observed at different doses. The effects of testosterone, catechin and nandrolone were not affected after perfusion with flutamide. Perfusion with diazoxide and U73122 nullified the effect of nandrolone (1 μM) and catechin (1 μM). Nandrolone and testosterone increased (45)Ca(2+) uptake with or without flutamide within 5min. These results indicate that nandrolone and catechin act through a receptor on the plasmatic membrane, as well as testosterone, showing a non-classical pathway in Sertoli cells from immature rat testes.

Effects of (-) epigallocatechin-3-gallate on Na(+) currents in rat dorsal root ganglion neurons

The natural product (-) epigallocatechin-3-gallate (EGCG) is the major polyphenolic constituent found in green tea. Dorsal root ganglion neurons are primary sensory neurons, and express tetrodotoxin-sensitive and tetrodotoxin-resistant Na(+) currents, which are both actively involved in the generation and propagation of nociceptive signals. Effects of EGCG on tetrodotoxin-sensitive and tetrodotoxin-resistant Na(+) currents in rat dorsal root ganglion neurons were investigated using the whole-cell variation of the patch-clamp techniques. EGCG inhibited both types of Na(+) currents potently and in a concentration-dependent manner. The apparent dissociation constant, K(d), was estimated to be 0.74 and 0.80 microM for tetrodotoxin-sensitive and tetrodotoxin-resistant Na(+) currents, respectively. (-) Epigallocatechin (EGC) was far less potent to inhibit Na(+) currents than EGCG, suggesting that gallate moiety of EGCG is an important functional group to modulate Na(+) currents. EGCG had little or no effect on the activation or steady-state inactivation voltage of either type of Na(+) current. EGCG simply reduced the availability of Na(+) channels for activation. Thus, EGCG appears to bind to resting Na(+) channels to inhibit them. EGCG slowed the recovery of tetrodotoxin-sensitive Na(+) current from inactivation. The property of EGCG to inhibit sensory Na(+) currents can be utilized to develop an analgesic agent.

Effects of EGCG on voltage-gated sodium channels in primary cultures of rat hippocampal CA1 neurons

(-)-Epigallocatechin-3-gallate (EGCG), the main active component of green tea, is commonly known for its beneficial properties at low doses. On the other hand, little is known about the adverse effects of EGCG. Voltage-gated sodium channel (VGSC) is responsible for both initiation and propagation of action potentials of the neurons in the hippocampus and throughout the central nervous system (CNS). In this study, the effects of EGCG on voltage-gated sodium channel currents (I(Na)) were investigated in rat primary cultures of hippocampal CA1 neurons via the conventional whole-cell patch-clamp technique. We found that I(Na) was not affected by EGCG at the concentration of 0.1microM, but was completely blocked by EGCG at the concentration of 400microM and higher, and EGCG reduced the amplitudes of I(Na) in a concentration-dependent manner in the range of 0.1-400microM. Furthermore, our results also showed that at the concentration of 100microM, EGCG was known to have the following performances: (1) it decreased the activation threshold and the voltage at which the maximum I(Na) current was evoked, caused negative shifts of I(Na) steady-state activation curve. (2) It enlarged I(Na) tail-currents. (3) It induced a left shift of the steady-state inactivation. (4) It reduced fraction of available sodium channels. (5) It delayed the activation of I(Na) in a voltage-dependent manner. (6) It prolonged the time course of the fast inactivation of sodium channels. (7) It accelerated the activity-dependent attenuation of I(Na). On the basis of these findings, we propose that EGCG could impair certain physiological functions of VGSCs, which may contribute, directly or indirectly, to EGCG's effects in CNS.

(-)-epigallocatechin gallate inhibits the pacemaker activity of interstitial cells of cajal of mouse small intestine

The effects of (-)-epigallocatechin gallate (EGCG) on pacemaker activities of cultured interstitial cells of Cajal (ICC) from murine small intestine were investigated using whole-cell patch-clamp technique at 30 and Ca(2+) image analysis. ICC generated spontaneous pacemaker currents at a holding potential of -70 mV. The treatment of ICC with EGCG resulted in a dose-dependent decrease in the frequency and amplitude of pacemaker currents. SQ-22536, an adenylate cyclase inhibitor, and ODQ, a guanylate cyclase inhibitor, did not inhibit the effects of EGCG. EGCG-induced effects on pacemaker currents were not inhibited by glibenclamide, an ATP-sensitive K(+) channel blocker and TEA, a Ca(2+)-activated K(+) channel blocker. Also, we found that EGCG inhibited the spontaneous [Ca(2+)](i) oscillations in cultured ICC. In conclusion, EGCG inhibited the pacemaker activity of ICC and reduced [Ca(2+)](i) oscillations by cAMP-, cGMP-, ATP-sensitive K+ channel-independent manner.

Effects of (--)-epigallocatechin-3-gallate on the activity of substantia nigra dopaminergic neurons

Despite many studies on the biological and pharmacological properties of (-)-epigallocatechin-3-gallate (EGCG), an active component of green tea, information on neuronal modulation by EGCG is limited. This study was designed to investigate the effects of EGCG on the electrical activity of rat substantia nigra dopaminergic neurons using whole-cell patch clamp recordings. The spike frequency was increased to 6.33+/-0.23 (p<0.05) and 7.15+/-0.29 (p<0.05) by 5 and 10 microM EGCG, respectively, from the control level of 5.49+/-0.19 spikes/second, respectively (n=18). The resting membrane potential of the cells was decreased to -45.66+/-0.45 and -43.99+/-0.87 (p<0.05), by 5 and 10 microM EGCG, respectively, from -47.82+/-0.57 mV. The amplitude of afterhyperpolarization was decreased to 12.73+/-0.45 (p<0.05) and 11.60+/-0.57 (p<0.05) by 5 and 10 microM EGCG, respectively, from 13.80+/-0.31 mV. The neuronal activity of dopaminergic neurons is closely linked to dopamine release. When neurons switch from a single-spike firing to bursts of action potentials, the release of dopamine increases. The above experimental results suggest that EGCG increases the neuronal activity via inhibition of calcium-dependent potassium currents underlying the afterhyperpolarization, and it could act as a facilitating factor that elicits NMDA-dependent bursts of action potentials like apamin or bicuculline methiodide.

Modulation of neuronal activity by EGCG

This study aims to investigate whether (-)-epigallocatechin-3-gallate (EGCG) affects neuronal activity of acutely isolated rat medial vestibular nuclear neurons in whole-cell configuration patch-clamp experiments. EGCG (0.5 and 1 muM) lowered the spontaneous firing rate and hyperpolarized the membrane potential of medial vestibular nuclear neurons. However, it did not change the amplitude of afterhyperpolarization or the spike width of the action potential. A second application of EGCG with the same concentration elicited lesser responses. These results suggest that EGCG decreases neuronal activity by affecting potassium currents which are responsible for membrane potentials.

Actions of orexins on individual myenteric neurons of the guinea-pig ileum: orexin A or B?

The actions of orexins (orexin A and B, 10-300 nM) on individual myenteric neurons of the guinea-pig ileum in vitro were compared using intracellular recording methods. Both orexins caused membrane depolarizations associated with an increase in input neuronal resistance in S and AH neurons via a direct action. Orexin depolarizations reversed at about -90 mV, indicating they were due to an inactivation of K+ channels. Orexins facilitated fast excitatory postsynaptic potentials without affecting postsynaptic sensitivity to acetylcholine and adenosine 5'-triphosphate, indicating that the peptides may facilitate ganglionic transmission by increasing presynaptic release of neurotransmitters. Orexin B was sometimes more effective than orexin A and vice versa. It is concluded that orexin B increased neuronal activity via mechanisms similar to orexin A in the guinea-pig myenteric plexus.

Actions of orexin-A in the myenteric plexus of the guinea-pig small intestine

Orexins and orexin-receptors are localized by displaying their immunoreactivity in the enteric nervous system. Intracellular recordings were made from isolated myenteric neurons to investigate actions of orexin-A in the myenteric plexus of the guinea-pig ileum. Superfusion of orexin-A caused membrane depolarizations in a subset of S and AH neurons. Orexin-A responses were preserved in Ca2+ free/high Mg2+ solution and associated with an increase in input membrane resistance; their reversal potential was about -90 mV. Orexin-A augmented nicotinic fast EPSPs, whereas it did not affect the postsynaptic sensitivity to acetylcholine; this indicates that orexin-A increased the presynaptic release of acetylcholine. In conclusion, orexin-A contributes in the regulation of gut motility via its pre- and postsynaptic actions in the myenteric plexus.

The effect of epigallocatechin gallate on intestinal motility in mice

OBJECTIVES

The epigallocatechin-3-gallate (EGCg) that is present in human diet originates mainly from tea leaves. Catechins have a number of possible application as medicines, however, there is no consistent evidence showing their influence on the gastrointestinal tract. Thus, the aim of the present study was to investigate the effect of EGCg on the motility of the murine isolated intestine.

METHODS

Segments of jejunum submerged in Krebs buffer were exposed to EGCg and the response was recorded under isometric conditions.

RESULTS

EGCg induced a dose-dependent inhibition of spontaneous activity in the jejunum. EGCg induced a decrease in the amplitude and frequency of jejunal contractions. moreover, the rythmicity of spontaneous, activity was altered in the presence of EGCg. A significant effect of EGCg was observed in the presence of 10(-4) M. The effect of EGCg was in part inhibited by pretreatment with methylene blue (guanylate cyclase inhibitor), while tetrodotoxin, (sodium channel blocker), L-nitro arginine methyl ester (nitric oxide synthase inhibitor), and N-ethylmaleimide (adenylate cyclase inhibitor) showed no effect.

CONCLUSIONS

The results of the present study suggest that EGCg inhibits the motility of the jejunum by direct action on smooth muscle cells where a guanylate cyclase-dependent mechanism may be partly involved.

Tea catechin, (-)-epigallocatechin gallate, facilitates cholinergic ganglion transmission in the myenteric plexus of the guinea-pig small intestine

Intracellular recordings were made from myenteric S neurons of the guinea-pig ileum. One of the major tea catechins, (-)-epigallocatechin gallate (EGCG at concentrations from 1 to 20 microM), was applied by superfusion to examine its effect on cholinergic ganglion transmission in the myenteric plexus. Fast excitatory postsynaptic potentials (EPSPs) evoked by electrical stimulation to ganglia and/or internodal fiber tracts were augmented in amplitude by EGCG in about 60% of tested neurons without changing the postsynaptic sensitivity to acetylcholine (ACh) applied by ionophoresis. Furthermore, the amplitude-ratio of paired fast EPSPs was increased by EGCG. These results indicated that the site at which EGCG augmented the fast EPSPs was presynaptic. It is concluded that EGCG can facilitate the cholinergic ganglion transmission possibly by increasing the amount of ACh released and, together with its previously described depolarizing action on myenteric neurons, may modulate the activity of the myenteric plexus of the guinea-pig ileum.