title: Evidence for Na+ independent active secretion of K+ and HCO - 3 by rat salivary duct epithelium.
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+.
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D001693:Biological Transport, Active / Q000187:drug effects; D004848:Epithelium / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D011188:Potassium / Q000378:metabolism*; D051381:Rats; D012964:Sodium / Q000378:metabolism*; D013363:Submandibular Gland / Q000378:metabolism*
chemical_list: D001639:Bicarbonates; D000584:Amiloride; D012964:Sodium; D011188:Potassium