Ba2+-inhibitable 86Rb+ fluxes across membranes of vesicles from toad urinary bladder.
86Rb+ fluxes have been measured in suspensions of vesicles prepared from the epithelium of toad urinary bladder. A readily measurable barium-sensitive, ouabain-insensitive component has been identified; the concentration of external Ba2+ required for half-maximal inhibition was 0.6 mM. The effects of externally added cations on 86Rb+ influx and efflux have established that this pathway is conductive, with a selectivity for K+, Rb+ and Cs+ over Na+ and Li+. The Rb+ uptake is inversely dependent on external pH, but not significantly affected by internal Ca2+ or external amiloride, quinine, quinidine or lidocaine. It is likely, albeit not yet certain, that the conductive Rb+ pathway is incorporated in basolateral vesicles oriented right-side-out. It is also not yet clear whether this pathway comprises the principle basolateral K+ channel in vivo, and that its properties have been unchanged during the preparative procedures. Subject to these caveats, the data suggest that the inhibition by quinidine of Na+ transport across toad bladder does not arise primarily from membrane depolarization produced by a direct blockage of the basolateral channels. It now seems more likely that the quinidine-induced elevation of intracellular Ca2+ activity directly blocks apical Na+ entry.
Department of Membrane Research, Weizmann Institute of Science, Rehovot, Israel.
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D000818:Animals; D001464:Barium / Q000494:pharmacology*; D002025:Bufonidae; D002414:Cations, Monovalent; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D005260:Female; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008297:Male; D010042:Ouabain / Q000494:pharmacology; D012413:Rubidium / Q000378:metabolism*; D012414:Rubidium Radioisotopes; D001743:Urinary Bladder / Q000378:metabolism*
D002414:Cations, Monovalent; D012414:Rubidium Radioisotopes; D001464:Barium; D010042:Ouabain; D012413:Rubidium