Summary
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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Supported by the Deutsche Forschungsgemeinschaft, grant Kn 138/1,3.
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Knauf, H., Lübcke, R. Evidence for Na+ independent active secretion of K+ and HCO −3 by rat salivary duct epithelium. Pflugers Arch. 361, 55–59 (1975). https://doi.org/10.1007/BF00587339
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DOI: https://doi.org/10.1007/BF00587339