Na+-H+ exchange in cardiac sarcolemmal vesicles.
The transport of Na+ by a purified sarcolemmal vesicular preparation from canine ventricular tissue was studied as a function of both internal and external pH. The uptake of Na+ into sarcolemmal vesicles increased upon raising the extravesicular pH of the reaction medium. Half-maximal uptake of Na+ was observed at a pHo of about 8.1 and maximal uptake occurred at pH 8.6. The uptake of Na+ by sarcolemma was also dependent upon the intravesicular pH. Na+ uptake into sarcolemmal vesicles was greatly attenuated in the absence of a H+ gradient across the membrane. Transport of Na+ was potently inhibited by amiloride, a known blocker of Na+-H+ exchange. LiCl was also an effective inhibitor of Na+ transport. In the presence of optimal H+ gradients, Na+ uptake was linear for the first 5 seconds of the reaction and exhibited a Vmax of 290 nmol Na+/mg per min and a KNa of 3.5 mM. These experiments strongly indicate the presence of a Na+-H+ exchange system in cardiac sarcolemma. This activity appeared to be relatively specific for this membrane fraction. The identification of Na+-H+ exchange activity in a sarcolemmal vesicular fraction from the heart will permit extensive characterization of the regulation and kinetics of this antiporter in future investigations.
Pierce
G N
GN
Philipson
K D
KD
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002499:Centrifugation, Density Gradient; D002712:Chlorides / Q000494:pharmacology; D004285:Dogs; D006859:Hydrogen / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008094:Lithium / Q000494:pharmacology; D018021:Lithium Chloride; D009206:Myocardium / Q000378:metabolism*; D012508:Sarcolemma / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*
D002712:Chlorides; D000584:Amiloride; D006859:Hydrogen; D008094:Lithium; D012964:Sodium; D018021:Lithium Chloride