Basolateral Na-H antiporter: uncoupled Na transport produces an amiloride-sensitive conductance.
An amiloride-inhibitable, Na(+)-H+ antiporter was identified in the basolateral membrane of turtle colon by measuring 22Na+ fluxes across isolated tissues apically permeabilized with the pore-forming antibiotic amphotericin B. In cells shrunken by exposure to Cl(-)-free (gluconate) solutions and treated with ouabain to block the Na-K-ATPase, Na+ movement across the basolateral membrane was due entirely to the antiporter. Elevation of cytosolic Na+ was associated with an amiloride-inhibitable outward current across the basolateral membrane. The sensitivity of the current to various amiloride analogues paralleled that of Na+ exchange rather than that of the apical Na+ channel. Furthermore, cell volume changes altered basolateral Na+ exchange and basolateral Na+ conductance in a parallel fashion. We propose that this amiloride-sensitive basolateral Na+ conductance represents an altered operating mode of a basolateral Na(+)-H+ exchanger.
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MA
Department of Physiology, University of Michigan Medical School, Ann Arbor 48109.
Dawson
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D000584:Amiloride / Q000494:pharmacology*; D000818:Animals; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism*; D003106:Colon / Q000166:cytology / Q000378:metabolism / Q000502:physiology; D004553:Electric Conductivity; D012964:Sodium / Q000378:metabolism* / Q000502:physiology; D017923:Sodium-Hydrogen Exchangers; D014426:Turtles
D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; D000584:Amiloride; D012964:Sodium