Author:
Chapman R. A.,Rodrigo G. C.,Tunstall J.,Yates R. J.,Busselen P.
Abstract
Hearts that have been perfused in low calcium fluids suffer, on return to normal calcium solutions, an impairment of function which can be irreversible-- the "calcium paradox." In hypothermic mammalian, amphibian, and fish heart the strong contracture, which is a typical first stage in the development of the calcium paradox, is reversible and appears to depend on a large rise in intracellular Na concentration ([Na]i), which occurs during the period of Ca deprivation. This rise is mainly due to a maintained inward Na flux through the Ca channels and causes a depolarization of the membrane potential, which stabilizes at about -20 mV. In frog atrial muscle if the membrane potential is clamped to values more negative than -50 mV during the period of Ca deprivation, no contracture develops on the restoration of the extracellular Ca concentration ([Ca]o). In all tissues the depolarization, the rise in [Na]i, and the Ca addition contracture are blocked by Ca channel blockers, antiarrhythmic drugs, and Mg ions if present in the Ca-free fluid. These agents are ineffective, however, if applied after a period of Ca deprivation when [Na]i has already risen. The influx of Ca ions, on Ca repletion, is therefore unlikely to be via the Ca channels and would seem to be through the Na-Ca exchange.
Publisher
American Physiological Society
Subject
Physiology (medical),Cardiology and Cardiovascular Medicine,Physiology
Cited by
39 articles.
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