Concentration-dependent actions of a new indene derivative, TN-871, in the enteric nervous system

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.

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

Intracellular recordings were made from enteric neurons in the myenteric plexus of the guinea-pig small intestine to examine actions of one of tea catechins, (-)-epigallocatechin gallate (EGCG), on neuronal activity. EGCG at concentrations from 1 to 20 microM depolarized about 60% of both of S and AH neurons in a concentration-dependent manner, although EGCG-induced depolarizations were largely varied in amplitude from neuron to neuron. The depolarizations started passing off during the presence of EGCG at higher concentrations, and became smaller or almost abolished with repeated applications, indicating the EGCG-induced response shows desensitization-like characteristics. The EGCG-depolarization was associated with a decrease in input membrane resistance, and their reversal potential was estimated about -30 mV. Since the EGCG-depolarization was recorded in the absence of external Ca(2+), it is concluded that one of tea catechins has direct depolarizing effects on a population of myenteric neurons.