Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P20020 (adenosine triphosphatase)
 3,299 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Exposure of the outside of the isolated frog skin to a Ringer's solution, made hypertonic by the addition of mannitol, causes a rapid and sustained increase in transepithelial permeability through a structural distortion-a focal blistering-of the "tight" junctions of the outermost living cell layer. [(3)H]ouabain, used as an autoradiographic marker for the Na+-pump (Na+-K+-adenosine triphosphatase), is usually unable to penetrate the frog skin from the outside solution, but when added to a hypertonic mannitol- Ringer's solution in the outside bath it readily penetrates the epithelium, presumably through the opened shunt pathway. Radioautographic analysis of [(3)H]ouabain binding sites revealed that most of ouabain enters from the outside solution binds to the sites on the cell membranes of the stratum spinosum, as was the case when it was applied from the inside bath in an earlier study. The outer living cell layer, the first to be exposed to ouabain, does not appear to be the major site for the Na+-pump, and therefore, is not likely to be responsible for most of the active pumping of Na+. This result demonstrates that previous failure to show a high density of Na+-pump sites on the cells of the outermost layer, when [(3)H]ouabain was applied from the inside solution, was not due to the inability of the marker to reach these cells at a sufficient concentration to reveal all pump sites. These results provide further support for a model of Na+-transport across the frog skin which distributes the active pump step on the inward facing membranes of all living cells.
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PMID:On the distribution of Na+-pump sites in the frog skin. 14 38

Ethanol (3%) decreases the potential difference and short-circuit current across the isolated frog skin in chloride Ringer's solution. Unidirectional fluxes of Na and Cl indicate that the drop in short-circuit current is due to an inhibition of the sodium influx. However, ethanol had no effect on the electrical parameters or sodium fluxes, when the frog skin was bathed in chloride-free solutions on both sides or the outside alone. The ethanol response is anion-dependent. In addition, chloride-free media in the inside bathing solution reduced the short-circuit current, indicating a sodium transport pathway which is dependent on chloride and confirming previous data in the literature. Other anions such as sulfate and nitrate could not substitute for chloride. The vasopressin-induced natriferic response and the ethanol effect were found to work independently of each other and different pathways of action are suggested for these agents. The intracellular sodium content of the isolated frog skin epithelium increased and potassium decreased in the presence of the Na-K adenosine triphosphatase inhibitor, ouabain, whereas ethanol or amiloride had no effect. The oxygen consumption of the isolated frog skin was unaffected by up to 10% ethanol. A general metabolic action is probably thus not mediating the response. Urea, in iso-osmotic concentrations to the ethanol, did not mimic its effect. Tritiated water fluxes (in the absence of an osmotic gradient) were reduced by 30% in the presence of 3% ethanol. It is suggested that ethanol may impede the flow of water across frog skin by a physicochemical interaction with membrane pores and the water molecules. The permeability coefficient (Ktrans) for ethanol was found to be 10 times smaller than the Ktrans for water.
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PMID:Effects of ethanol on the permeability of frog skin. 108 5

Electrogenic Na absorption, independent of either nutrients or other ions, occurs in the rabbit ileum. However, unlike electrogenic Na absorption in the distal colon and other tight epithelia, this ileal transport system is not inhibited by amiloride. Because of this amiloride insensitivity, ileal electrogenic Na absorption has been poorly characterized. To more clearly delineate the underlying mechanisms of this pathway, we examined the effects of phenamil, an amiloride analogue, on ion fluxes and electrical parameters in rabbit ileum in vitro under short-circuit conditions. Phenamil has been shown to have a high affinity for Na channels, but minimal effect on Na-H exchange. Amiloride (10(-8) through 10(-4) M) had a minimal effect on short-circuit current. In contrast, phenamil induced a significant decrease in short-circuit current; the maximal effect was seen at 10(-4) M phenamil. There was an associated decrease in conductance at 10(-4) M phenamil. Ion flux studies were performed in normal, chloride-free and bicarbonate-free Ringer's solution; under each condition, 10(-4) M phenamil inhibited mucosal-to-serosal Na flux, net Na flux, and short-circuit current without significantly altering other fluxes. Phenamil did not inhibit the electrical response to either 10 mM glucose or 1 mM theophylline, indicating that the drug did not block either nutrient-coupled electrogenic Na absorption or electrogenic Cl secretion, and did not inhibit sodium-potassium-stimulated adenosine triphosphatase. These results demonstrate that electrogenic Na absorption in rabbit ileum may be blocked by the amiloride analogue phenamil, suggesting that, in this epithelium, Na absorption may occur via Na channels in which the amiloride-binding site has been significantly altered.
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PMID:Phenamil inhibits electrogenic sodium absorption in rabbit ileum. 253 78