ABSTRACT
Since the pioneering work of Ussing & Zerahn (1951), the design of short-circuit apparatus has been modified only slightly. Such chambers generally consist of two halves, between which the epithelium is stretched. The assembly is clamped together and filled with saline, which is circulated in each half chamber by gas lift pumps, usually connected to the main chamber with plastic pipes. There are two current electrodes, one at each end of the chamber, and -usually -two voltage-sensing electrodes close to the tissue. The current passed through the chamber is adjusted until the p.d. between the sensing electrodes becomes zero. Under such conditions, only actively transported ions move across the tissue, and the short-circuit current is a precise measure of the net flux of charged species. Short-circuiting is thus a method of choice for investigating transport phenomena in epithelia.
