The action of aldosterone on Na+ and K+ transport in the rat submaxillary main duct

Summary The main excretory duct of the submaxillary gland of normal and adrenalectomized rats was perfused with bicarbonate Ringer's solution and the following values were measured: the transepithelial electrical potential difference, the specific electrical resistance of the epithelium, and the transepithelial net fluxes for Na⁺ and K⁺. From the potential difference and the resistance, the short circuit current was calculated. Following adrenalectomy the short circuit current dropped to about one half, while the electrical resistance increased around twofold and the transepithelial potential difference remained constant. The reduction of short circuit current was accompanied by a 30% reduction of Na⁺ reabsorption whereas K⁺ secretion was only slightly diminished Acute substitution of aldosterone to adrenalectomized animals led to a restitution of the Na⁺ fluxes and showed a tendency to increase K⁺ secretion. Following the administration of Actinomycin D to normal animals, Na⁺ resorption declined as in adrenalectomized rats but K⁺ secretion remained essentially unchanged. From these observations it is concluded that the hypothetical aldosterone-induced proteins act only on Na-resorption and that they may act by both increasing the sodium permeability of the luminal cell membrane and stimulating active Na⁺ transport. The latter effect does not seem to consist of a non specific enhancement of the energy supply since it does not influence the active potassium secretion of the cell.