The Ussing chamber
To functionally characterise gastrointestinal epithelia we use the voltage clamp Ussing technique. With this method we can measure two major functions of the mucosa: The transepithelial transport function (resorptive and secretive) and the barrier function between the inner and the outer millieu. The Ussing technique allows also to evaluate nerval and distension evoked secretion of the mucosa. Through the addition of substances that either enhance or inhibit secretion we can identify cellular mechanisms, neuronal circuits, neurotransmitters and -receptors or ion channels. In an Ussing chamber, the epithelium lies between two symmetric, electrolyte filled chambers. The epithelium causes a spontaneous transepithelial voltage difference (VEP) which can be measured. The current that has to be applied to compensate ("clamp") this voltage difference to zero is called the short circuit current ISC. It reflects the net charge flux through the epithelium. In our setups we can use mucosa/submucosa preparations from fresh tissue (human or animal) or epithelial cell lines.
The transport of ions through the epithelium, in particular the secretion of chloride, play an important role in the gut. They are regulated primarily by the sumucous plexus (a division of the enteric nervous system). However, also sensory afferents may modulate this regulation. If this system gets out of balance it can result in severe functional disturbances (e.g. irritable bowel syndrome, IBS).