TNF-alpha changes the electrophysiological properties of myenteric neurones via cyclooxygenase metabolites and protein tyrosine phosphorylation; the cells primarily responding to the cytokine seem to be non-neuronal cells in the ganglion culture, which respond with a nuclear STAT5 translocation suggesting an action on gene transcription.

No abstract

Short-chain fatty acids produced by the bacterial fermentation of carbohydrates are present in high concentrations within the colonic lumen and have been shown to alter the excitability of enteric neurones. The present study was designed to investigate the mechanisms of butyrate-induced changes in membrane potential of myenteric neurones. Myenteric neurones from 4-10-day-old rats were isolated from the small and large intestine by an enzymatic digestion with collagenase and kept in culture. Membrane potential was measured with the whole-cell patch-clamp technique and the intracellular Ca2+ concentration was measured with the fura-2 method. The short-chain fatty acid butyrate (10-100 mmol L(-1)) induced a reversible and concentration-dependent hyperpolarization of the membrane with a half-maximal effect at 30 mmol L(-1). The hyperpolarization evoked by butyrate (50 mmol L(-1)) was strongly inhibited by charybdotoxin (10(-7) mol L(-1)), a specific blocker of Ca2+ -dependent K+ channels. The butyrate-induced hyperpolarization was resistant against blockade of phospholipase C by U-73122 (10(-5) mol L(-1)), and resistant against inclusion of heparin (6 x 10(-6) mol L(-1)), an inositol-1,4,5-trisphosphate receptor antagonist, in the patch-pipette. In contrast, ruthenium red (3 x 10(-5) mol L(-1)), an inhibitor of ryanodine receptors, significantly reduced both the hyperpolarization of the membrane as well as the increase in the intracellular Ca2+ concentration evoked by butyrate. Even in neurones permeabilized with saponin (10 mg L(-1)), butyrate was able to stimulate a release of stored intracellular Ca2+ suggesting a direct action of the short-chain fatty acid at the stores without mediation of a soluble intracellular second messenger.

Permeable supports with A6 cell monolayers were mounted in an Ussing chamber and bilaterally bathed with Ringer solution at room temperature. Short-circuit current (Isc) was recorded continuously, and noise analysis revealed microscopic channel current characteristics. Our investigation focuses on the stimulation of apical Na+ entry caused by exposing the serosal surface of the A6 cell monolayers to hyposmotic Ringer solution. To evaluate the possible role of the cytoskeleton in the regulation of Na+ channels in response to a change in osmolality we used four different experimental approaches. In the control group, which were not exposed to any cytoskeleton-influencing drugs, there was a 1.5-fold increase in Isc and in the number of open Na+ channels after osmotic stimulation. For the second group cytochalasin D (0.1 microg/ml) was present on the serosal side during the experiments. Neither Isc nor the number of open Na+ channels increased after osmotic stimulation. In the third group colchicine (0.2 mM) or nocodazole (20 microM) was present on the serosal side, which resulted in 1.8-fold and 1.5-fold increases in Isc as well as 3-fold and 2-fold increases in the number of Na+ channels, respectively. In the fourth experimental group erythro-9-(2-hydroxy-3-nonyl) adenine hydrochloride (EHNA, 0.5 mM), a dynein inhibitor, was present on the serosal side. In this group Isc decreased to about 0.4 microA/cm2, and subsequent application of amiloride abolished Isc completely. Under hyposmolar conditions EHNA abolished entirely the sensitivity of Isc to the osmotic challenge. Because of the EHNA-induced down-regulation of Isc, the density of apical Na+ channels in this experimental group could not be determined. These results show that the cytoskeleton is dominantly involved in osmotic channel regulation at the apical membrane, and that actin filaments, microtubules and molecular motors are involved in the recruitment of additional Na+ channels.

Intact myenteric ganglia from 4- to 10-day-old rats were isolated from the small intestine. The preparations were cultured overnight, and drugs were applied within this time frame (20 h). Whole cell patch-clamp technique was used to measure basal membrane potential and carbachol-induced depolarization at neurons within these ganglia. Pretreatment with TNF-alpha (100 ng/ml) hyperpolarized the membrane (from -31.0 +/- 2.7 mV under control conditions to -61.2 +/- 3.2 mV in the presence of the cytokine) and potentiated the depolarization induced by carbachol (from 5.2 +/- 0.7 mV under control conditions to 27.5 +/- 2.0 mV in the presence of the cytokine). These effects were mimicked by carbocyclic thromboxane A2 (10(-6) mol/l), a stable thromboxane A2 agonist. The TNF-alpha action was inhibited by 1-benzylimidazole (2 x 10(-4) mol/l), a thromboxane synthase inhibitor, and BAY U 3405 (5 x 10(-4) mol/l), an inhibitor of thromboxane receptors. Measurements of thromboxane production in the supernatant of the culture revealed an increased concentration of thromboxane B2, the stable metabolite of thromboxane A2, after exposure to TNF-alpha. Immuncytochemical staining for cyclooxygenase-2 (COX-2) and the neuronal marker microtubule-associating protein-2 revealed an upregulation of COX-2 in myenteric neurons after exposure to the cytokine. These results demonstrate the involvement of COX-2 and the subsequent production of thromboxane A2 in the presence of TNF-alpha.