The<unk>  provides a system to measure the transport of ions, nutrients, and drugs across various epithelial tissues, (although can generate false-negative results for lipophilic substances). It consists of two halves separated by the epithelia (sheet of mucosa or monolayer of epithelial cells grown on permeable supports). Epithelia are polar in nature, i.e., they have an apical or mucosal side and a basolateral or serosal side. An<unk>  can isolate the apical side from the basolateral side. The two half chambers are filled with equal amounts of symmetrical Ringer solution to remove chemical, mechanical or electrical driving forces. Ion transport takes place across any epithelium. Transport may be in either direction. Ion transport produces a potential difference (voltage difference) across the epithelium. The voltage is measured<unk>  two voltage electrodes placed near the tissue/epithelium. This voltage is cancelled out by injecting current,<unk>  two other current electrodes placed away from the epithelium. This short-circuit current (Isc) is the measure of net ion transport. Measuring epithelial ion transport is helped by<unk> s. The voltage result from this ion transport is easy to accurately measure. The epithelium pumps ions from one side to the other and the ions leak back through so-called tight junctions that are situated between the epithelial cells. To measure ion transport, an external current is applied. Simply cancelling the voltage underestimates the true value. This is corrected by a short circuit at the voltage measuring electrodes. The resistance between the external voltage electrodes must be considered. The Isc underestimates the ion transport: the error can be as much as 10-fold. The type of chambers suggested by<unk>  produces large errors. This error is often estimated by measuring the voltage without tissue present, leading to uncertain values. Better methods involve<unk>  alternating current in the form of sinuous-shaped current<unk>  several frequencies, square wave pulses, sharp impulses and random noise.
Ussing chamber
Cooling center
Drip chamber
Diving chamber
Optic cup 
Layer of rods and cones
Fluid compartments
Neuroeffector junction