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Na+-Ca2+ exchange activity is high in cardiac sarcolemmal vesicles suggesting an important physiologic role. Vesicular Na+-Ca2+ exchange, however, is usually measured under conditions which are far from physiologic. Using sarcolemmal vesicles, we have estimated the possible significance of both Ca2+ influx and efflux mediated by Na+-Ca2+ exchange under approximate in vivo ionic conditions. In this situation, Na+-Ca2+ exchange activity is far from maximal with intracellular Mg2+ causing significant inhibition. The capacity of the Na+-Ca2+ exchange system to extrude intracellular Ca2+ (at [Ca2+] = 6.0 microM) is about 1.2 mumol Ca2+/kg wet weight/s and approximately equals the capacity of the sarcolemmal ATP-dependent Ca2+ pump. The capacity of the sarcoplasmic reticular Ca2+ pump to remove cytoplasmic Ca2+ is much larger. Significant Ca2+ influx through the exchanger is unlikely to occur in normal mammalian myocardium and would require reduced extracellular Na+ or elevated intracellular Na+.
K D Philipson, and
R Ward
January 1987,
The American journal of physiology,
K D Philipson, and
R Ward
May 1982,
The Journal of biological chemistry,
K D Philipson, and
R Ward
November 1987,
The American journal of physiology,
K D Philipson, and
R Ward
January 1988,
Molecular and cellular biochemistry,
K D Philipson, and
R Ward
November 1988,
Molecular and cellular biochemistry,
K D Philipson, and
R Ward
January 1985,
The Canadian journal of cardiology,
K D Philipson, and
R Ward
March 1998,
The American journal of physiology,
K D Philipson, and
R Ward
July 1999,
The Journal of experimental biology,
K D Philipson, and
R Ward
July 1988,
Biochemical and biophysical research communications,
K D Philipson, and
R Ward
September 1988,
The American journal of physiology,
