Demonstration of a Na+/H+ exchange activity in purified canine cardiac sarcolemmal vesicles

S. M. Seiler, E. J. Cragoe, Larry Jones

Research output: Contribution to journalArticle

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Abstract

Purified canine cardiac sarcolemmal membrane vesicles exhibit a sodium ion for proton exchange activity (Na+/H+ exchange). Na+/H+ exchange was demonstrated both by measuring rapid 22Na uptake into sarcolemmal vesicles in response to a transmembrane H+ gradient and by following H+ transport in response to a transmembrane Na+ gradient with use of the probe acridine orange. Maximal 22Na uptake into the sarcolemmal vesicles (with starting intravesicular pH = 6 and extravesicular pH = 8) was approximately 20 nmol/mg protein. The extravesicular K(m) of the Na+/H+ exchange activity for Na+ was determined to be between 2 and 4 mM (intravesicular pH = 5.9, extravesicular pH = 7.9), as assessed by measuring the concentraton dependence of the 22Na uptake rate and the ability of extravesicular Na+ to collapse an imposed H+ gradient. All results suggested that Na+/H+ exchange was reversible and tightly coupled. The Na+/H+ exchange activity was assayed in membrane subfractions and found most concentrated in highly purified cardiac sarcolemmal vesicles and was absent from free and junctional sarcoplasmic reticulum vesicles. 22Na uptake into sarcolemmal vesicles mediated by Na+/H+ exchange was dependent on extravesicular pH, having an optimum around pH 9 (initial internal pH = 6). Although the Na+/H+ exchange activity was not inhibited by tetrodotoxin or digitoxin, it was inhibited by quinidine, quinacrine, amiloride, and several amiloride derivatives. The relative potencies of the various inhibitors tested were found to be: quinacrine > quinidine = ethylisopropylamiloride > methylisopropylamiloride > dimethylamiloride > amiloride. The Na+/H+ exchange activity identified in purified cardiac sarcolemmal vesicles appears to be qualitatively similar to Na+/H+ exchange activities recently described in intact cell systems. Isolated cardiac sarcolemmal vesicles should prove a useful model system for the study of Na+/H+ exchange regulation in myocardial tissue.

Original languageEnglish
Pages (from-to)4869-4876
Number of pages8
JournalJournal of Biological Chemistry
Volume260
Issue number8
StatePublished - 1985

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Amiloride
Canidae
Quinacrine
Quinidine
Demonstrations
Digitoxin
Membranes
Acridine Orange
Tetrodotoxin
Protons
Sodium
Ions
Tissue
Derivatives
Ion Exchange
Sarcoplasmic Reticulum
Proteins

ASJC Scopus subject areas

  • Biochemistry

Cite this

Demonstration of a Na+/H+ exchange activity in purified canine cardiac sarcolemmal vesicles. / Seiler, S. M.; Cragoe, E. J.; Jones, Larry.

In: Journal of Biological Chemistry, Vol. 260, No. 8, 1985, p. 4869-4876.

Research output: Contribution to journalArticle

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