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Abstract

The short-circuit-current (SCC), which is generated by the epithelium of the main excretory duct of human salivary glands, was determined.
For technical reasons direct short-circuiting of a well defined epithelial area was not feasible, so the following approach was used. The transepithelial electrical potential difference (PD) was measured under open circuit conditions and the specific resistance of the epithelium [R_m(ω·cm²)] was determined by applying the principles of cable analysis.
According to Ohm's law SCC = PDR_m.
This experimental approach is valid since R_m was constant throughout the current range required.
The experimental techniques were as follows: The salivary main ducts were catheterized with a multibarreled catheter. One barrel served for perfusion of the duct with a modified Ringer's solution and for measuring the open circuit PD. Another barrel was used for injection of current pulses, and with the remaining barrels the attenuation of the applied voltage was measured along the axis of the duct.
In the submaxillary duct the effective resistance was 325±18 ω, and the length constant was 0.69±0.04 cm. These values yielded a specific resistance of the epithelial wall of 365±33 ω · cm². With the transepithelial PD of 65±6 mV, the SCC was calculated to be 178±24 μA/cm². In theparotid duct similar data were obtained resulting in a SCC of 160±15 μA/cm².
Data from the preceding papers and from the literature suggest that the SCC is the result of active resorption of sodium and active secretion of potassium and probably also of bicarbonate.