Item

Abstract

An approximately 1 cm length of the main excretory duct of the rabbit submaxillary gland is dissected free from the animal and transferred to a lucite perfusion chamber containing rabbit serum. The ends of the duct are mounted over a pair of capillaries so that the duct could be perfused through one capillary while samples are collected from the other. A special multibarrelled perfusion system allowed intraluminal current application and transepithelial voltage recording. Both sides of the duct epithelium were bathed with continuously flowing solutions, which could be rapidly exchanged.

Net Na⁺ transport across the isolated duct is as great as net Na⁺ transport in vivo. Net Na⁺ reabsorption ranges from 380 to 600 neq/min·cm², and net K⁺ secretion is 13 to 26 neq/min·cm². Cation transport is maintained stable during a 3 h period, and thereafter slowly decreases. During perfusion with bicarbonate Ringer's solution, the mean transepithelial electrical potential difference is 17±3 mV (lumen negative). During sodium sulfate perfusion the duct epithelium generates a p.d. of up to 185 mV. Using cable analysis, the specific electrical resistance of the duct epithelium was determined to be 11.2±1.6 Ωcm². Since the duct epithelium shows a linear current-voltage relation, the short-circuit-current can be calculated from the open-circuit-p.d. and the specific wall resistance during perfusion with bicarbonate Ringer's solution. A value of 1.5±0.3 mA/cm² is obtained, which is primarily accounted for by active transport of sodium.