Abstract
Low (therapeutic) concentrations of cardiotonic steroids (CTS) inhibit the ubiquitous Na pump in a variety of types of cells including cardiac and vascular smooth muscle cells, neurons and kidney tubule cells. Since these cells also have Na +Ca 2+ exchangers in their plasma membrane, partial Na pump inhibition causing [Na +] in to rise will also result in a rise in [Ca 2+] in. With a stoichiometry of about 3 Na +:1 Ca 2+, a small change in [Na +] in may be associated with a relatively large increase in [Ca 2+] in. These effects can account for the direct cardiotonic action of CTS in cardiac muscle and can explain the effects of CTS on the kidneys, nervous system and vascular smooth muscle. Mordecai Blaustein focusses initially on direct cellular actions of CTS on cardiac muscle, then compares their effects on other tissues. He explains that the therapeutic action of CTS in patients with congestive heart failure appears to be the result of CTS action on one or more of these organs.
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