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  • Title: Evidence for Na+ independent active secretion of K+ and HCO - 3 by rat salivary duct epithelium.
    Author: Knauf H, Lübcke R.
    Journal: Pflugers Arch; 1975 Dec 19; 361(1):55-9. PubMed ID: 1239742.
    Abstract:
    In order to elucidate whether or not active secretion of potassium and bicarbonate by the rat submaxillary duct epithelium operates independently of sodium reabsorption, Na+ transport was blocked by amiloride, which is known to inhibit Na+ entry from lumen into cell. With 10(-4) M amiloride in HCO - 3 -Ringer at the luminal side, the transepithelial electrical potential difference approached zero, the Na+ conductance of the luminal cell membrane was drastically reduced, and the K+ conductance was significantly reduced. Net K+ secretion was reduced by 80%, whereas net HCO - 3 secretion was significantly increased. The remaining 20% of net K+ secretion proceeded at zero net Na+ transport and in the absence of significant chemical and electrical potential differences between lumen and interstitium of the duct. This active component of net K+ secretion was accompanied by an equal rate of active HCO - 3 secretion. These findings confirm the independence of this active secretion of K+ and HCO - 3 from Na+ transport. They indicate an electrically neutral secretion of K+ and HCO - 3, probably by the postulated luminal K+ -H+ -exchange mechanism. The 80% of net K+ secretion, which were abolished by amiloride together with Na+ reabsorption, seem to be functionally coupled with Na+ transport. The linkage of K+ -to- Na+ is probably mediated by a luminal carrier exchanging Na+ for K+ and H+.
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