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The transport of L-alanine and L-leucine into membrane vesicles isolated from mature canine ventricular myocardium was studied. Transport was assessed in purified sarcolemma and in vesicles differentially enriched either for sarcolemma or sarcoplasmic reticulum to further localize these transport systems. An imposed inward gradient of a NaNO3 stimulated uptake of L-alanine but not L-leucine by these vesicles. Amino acid uptake by these vesicles occurred into an osmotically active space. The stimulatory effect of Na+ on alanine transport was most striking in the purified sarcolemma vesicles, where Na+-stimulated alanine flux was 45 +/- 14 pmol X mg-1 X min-1. Furthermore, Na+-dependent alanine transport activity appeared to copurify with Na+-K+-ATPase activity, which served as a marker for sarcolemma membrane when these activities were compared in the three different membrane preparations. Leucine transport by sarcolemma was not altered by an imposed Na+ gradient. However, leucine uptake was a saturable function of extravesicular leucine and was inhibited by valine. In contrast, in sarcoplasmic reticulum membrane vesicles leucine uptake increased proportionately with increasing media leucine and was unaffected by valine. Our results demonstrate the feasibility of directly studying the transport of naturally occurring amino acids in membrane vesicles from mammalian heart, and the presence of Na+-dependent alanine transport system and a Na+-independent leucine transporter in the sarcolemma but not in sarcoplasmic reticulum of canine ventricular myocardium.
L H Young, and
B L Zaret, and
E J Barrett
August 2009,
Bioscience reports,
L H Young, and
B L Zaret, and
E J Barrett
October 1978,
Biochimica et biophysica acta,
L H Young, and
B L Zaret, and
E J Barrett
July 1974,
Annals of the New York Academy of Sciences,
L H Young, and
B L Zaret, and
E J Barrett
December 1974,
Archives of biochemistry and biophysics,
L H Young, and
B L Zaret, and
E J Barrett
December 1972,
American journal of veterinary research,
L H Young, and
B L Zaret, and
E J Barrett
January 1990,
Journal of internal medicine. Supplement,
L H Young, and
B L Zaret, and
E J Barrett
January 1987,
Ukrainskii biokhimicheskii zhurnal (1978),
L H Young, and
B L Zaret, and
E J Barrett
August 1990,
The Journal of biological chemistry,
L H Young, and
B L Zaret, and
E J Barrett
January 1990,
Progress in clinical and biological research,
L H Young, and
B L Zaret, and
E J Barrett
January 1978,
The American journal of physiology,
