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At least 253 records · Page 14Linked to original sources
PubMed1975

Evidence for Na+ independent active secretion of K+ and HCO - 3 by rat salivary duct epithelium.

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+.

Amiloride↗
PubMed1975

H+ transport and membrane-bound HCO - 3 ATPase in salivary duct epithelium.

An ATPase stimulated by HCO - ions and other oxybases and inhibited by SCN- has been found in main excretory duct of rat submaxillary gland, a tissue, capable of actively secreting HCO - 3 ions. No such ATPase was found in the rabbit duct, which normally does not secrete HCO - 3. The HCO - 3 ATPase was localized in the plasma membrane fraction of the homogenate, as evidenced by the marker 5'-nucleotidase. The activities of the HCO - 3 ATPase increased in metabolic alkalosis and decreased in metabolic acidosis in parallel to secretion of HCO - 3 and K+ ions by the duct epithelium. These findings provide further evidence that the membrane-bound HCO - 3 ATPase is involved in active H+/HCO - 3 transport.

Adenosine Triphosphatases↗
PubMed1984

Effects of adrenergic agonists on electrolyte transport in perfused salivary duct of rat.

The Na and Cl absorption and K secretion that occur in the main duct of rat submandibular gland are affected by adrenergic actions. The specific effects of stimulation of alpha-, beta 1- and beta 2-adrenergic receptors on net transepithelial fluxes of Na, K and Cl were investigated in microperfused main excretory duct of rat submandibular gland. Administration of methoxamine (2.5 micrograms . kg-1 . min-1, i.v.) resulted in marked decreases in net efflux (or absorption) of Na (38%) from the duct into the interstitial fluid and net influx (or secretion) of K (20%) from interstitial fluid into the ductal lumen without any effect on net efflux or reabsorption of Cl. A higher dose of methoxamine (5 micrograms . kg-1 . min-1, i.v.) produced further inhibition of net fluxes of Na and K without affecting net flux of Cl. Dobutamine (50 micrograms . kg-1 . min-1, i.v.) enhanced net effluxes of Na (40%) and Cl (300%) from the lumen but did not alter net K influx into the lumen. When the dosage of dobutamine was increased to 200 micrograms . kg-1 . min-1, an inhibition of net influx of K (28%) into ductal fluid was observed in addition to enhanced net fluxes of Na and Cl from the lumen. Administration of terbutaline (15 and 30 micrograms . kg-1 . min-1, i.v.) decreased net influx of K (30-40%) and increased net efflux of Cl (280%) without affecting net efflux of Na.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1979

Changes in the main submandibular salivary duct of rabbits resulting from ductal ligation.

Normal submandibular ducts from rabbits have been examined by mucosubstance histochemistry, transmission and scanning electron microscopy. The results were compared with the appearances of ducts removed 4...6 weeks after ligation. The normal ducts were composed mainly of columnar "light" cells and basal cells but, in addition, some "dark" cells and scattered goblet containing sulphated mucins were always present. The luminal surface of the ductal cells possessed numerous microvilli protruding into the lumen, and a rim of negatively charged mucin was present on this surface of these cells. After ligation the ducts became greatly distended by their fluid contents which remained under pressure until the duct was incised. The epithelial cells were flattened and appeared to contain less cytoplasm per cell; "light" cells, basal cells and "dark" cells were still recognisable. Goblet cells were much more plentiful than in the control ducts and often protruded into the lumen despite the increased intraluminal pressure. The development of a number of ciliated cells had also occurred and they were often situated close to goblet cells. Lymphatic vessels were more prominent around the ligated ducts. Luminal microvilli were less numerous than in the control ducts but the rim of negatively charged mucin on the luminal surface of ductal cells was more conspicuous. Mixed inflammatory cells were present within the lumina of ligated ducts especially in those parts adjacent to the ductal cells. No inflammatory cell has been observed passing through the wall of a main duct and the possibility exists that these cells had entered lumina within the gland and migrated from there to the main duct. The above findings may serve to help our understanding or physiological events in the ducts.

Animals↗