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Journal of Pharmacology And Experimental Therapeutics, Vol. 143, Issue 1, 107-119, 1964
Copyright © 1964 by American Society for Pharmacology and Experimental Therapeutics

THE EFFECTS OF EXTERNAL CALCIUM CONCENTRATION ON THE DISTRIBUTION AND EXCHANGE OF CALCIUM IN RESTING AND BEATING GUINEA-PIG AURICLES

A. Grossman 1 and Robert F. Furchgott 1

1 Department of Pharmacology, State University of New York Downstate Medical Center, Brooklyn, New York

The extracellular space of the isolated electrically stimulated (1/sec) guinea-pig left auricle was estimated with inulin, thiocyanate, and Cl36. Spaces of 20.9, 40.9, and 40.2 ml/100 g wet weight were determined for these substances, respectively.

A study of the relationship between the calcium concentration of the medium and the calcium content of the auricle, at various external concentrations of calcium, indicated that calcium is distributed in the auricle in at least three fractions or "compartments": (1) an extracellular fraction; (2) a difficultly exchangeable fraction which is presumably intracellular; and (3) an "unaccounted for" fraction.

Studies of the exchange of Ca45 (between the medium and the isolated auricle), during 5-minute incubation periods at various external concentrations of calcium, of resting and stimulated auricles, indicated that a greater amount of Ca45 exchanged with tissues that were contracting. However, there was no demonstrable difference in the total amount of calcium, between the contracting and resting auricles. It seemed that an additional amount of calcium, that was already within the auricle, became exchangeable during contraction. The calcium in the tissue that was associated with the contractile process is believed to be part of the "unaccounted for" fraction. Under the conditions employed, approximately 20% of the total muscle calcium is associated with the contractile process at near maximal contraction. Also, a correlation appeared to exist between the amplitude of contraction and the fraction of the total tissue calcium that exchanged.

Submitted on May 14, 1963
Accepted on September 11, 1963




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E. S. Nieuwendijk, F. L. Meijler, and D. Durrer
Influence of Paired Stimulation on the Electro-mechanical Dissociation During Low Calcium Perfusion of Isolated Rat Hearts
Cardiovasc Res, October 1, 1967; 1(4): 308 - 312.
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