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Am J Physiol Heart Circ Physiol 259: H712-H719, 1990;
0363-6135/90 $5.00
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AJP - Heart and Circulatory Physiology, Vol 259, Issue 3 712-H719, Copyright © 1990 by American Physiological Society

ARTICLES

Transient inotropic effects of low extracellular sodium in perfused rat heart

F. Kolar, W. C. Cole, B. Ostadal and N. S. Dhalla
Division of Cardiovascular Sciences, St. Boniface General Hospital Research Centre, Winnipeg, Manitoba, Canada.

The inotropic effects of low concentrations of extracellular Na+ (35-110 mM) were studied using Langendorff-perfused rat hearts. Low Na+ induced an initial positive inotropic response proportional to the decrease of transsarcolemmal Na+ gradient. At 35 mM Na+, this effect was followed by a secondary fall in contractility and rise of resting force (RF) and then by a delayed positive inotropic effect and recovery of RF. The magnitude of these low Na(+)-induced transient changes was dependent on the extracellular Ca2+ concentration and was altered by amiloride (6 x 10(-4) and 2.5 x 10(-3) M), ouabain (5 x 10(-5) and 5 x 10(-4) M), ryanodine (2 x 10(-8), 1 x 10(-7) and 1 x 10(-6) M), and sodium azide (1 x 10(-3) and 5 x 10(-3) M) but not by verapamil (2 x 10(-8) and 1 x 10(-7) M) or vanadate (4 x 10(-6) M). The data indicate the initial positive inotropic response of the rat heart to low Na+ may be due to rapid loading of myocytes with Ca2+ through the Na(+)-Ca2+ exchange mechanism. The secondary depression of contractility and the rise of RF appear to be the consequence of the short-lived intracellular Ca2+ overload. Furthermore, the recovery of contractions and the delayed positive inotropic response may be the result of the intracellular redistribution of excessive Ca2+ into the sarcoplasmic reticulum with mitochondria and increased transsarcolemmal Ca2+ efflux apparently playing a more minor role.


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H. K. Saini and N. S. Dhalla
Modification of intracellular calcium concentration in cardiomyocytes by inhibition of sarcolemmal Na+/H+ exchanger
Am J Physiol Heart Circ Physiol, December 1, 2006; 291(6): H2790 - H2800.
[Abstract] [Full Text] [PDF]


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