Coupled Na+/H+ exchange in rat parotid basolateral membrane vesicles.
pH gradient-dependent sodium transport in highly purified rat parotid basolateral membrane vesicles was studied under voltage-clamped conditions. In the presence of an outwardly directed H+ gradient (pHin = 6.0, pHout = 8.0) 22Na uptake was approximately ten times greater than uptake measured at pH equilibrium (pHin = pHout = 6.0). More than 90% of this sodium flux was inhibited by the potassium-sparing diuretic drug amiloride (K1 = 1.6 microM) while the transport inhibitors furosemide (1 mM), bumetanide (1 mM), SITS (0.5 mM) and DIDS (0.1 mM) were without effect. This transport activity copurified with the basolateral membrane marker K+-stimulated p-nitrophenyl phosphatase. In addition, 22Na uptake into the vesicles could be driven against a concentration gradient by an outwardly directed H+ gradient. pH gradient-dependent sodium flux exhibited a simple Michaelis-Menten-type dependence on sodium concentration consistent with the existence of a single transport system with KM = 8.0 mM at 23 degrees C. A component of pH gradient-dependent, amiloride-sensitive sodium flux was also observed in rabbit parotid basolateral membrane vesicles. These results provide strong evidence for the existence of a Na+/H+ antiport in rat and rabbit parotid acinar basolateral membranes and extend earlier less direct studies which suggested that such a transporter was present in salivary acinar cells and might play a significant role in salivary fluid secretion.
Manganel
M
M
Clinical Investigations and Patient Care Branch, National Institute of Dental Research, Bethesda, Maryland 20892.
Turner
R J
RJ
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001485:Basement Membrane / Q000378:metabolism; D001693:Biological Transport, Active; D002352:Carrier Proteins / Q000378:metabolism*; D002499:Centrifugation, Density Gradient; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008297:Male; D010306:Parotid Gland / Q000378:metabolism* / Q000648:ultrastructure; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers
D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; D000584:Amiloride; D012964:Sodium