Measurement of rapidly exchangeable cellular calcium in the perfused beating rat heart.

Publisher Website
Google Scholar
Abstract
Although Ca2+ plays a vital role in excitation-contraction coupling in the heart, investigation of the details of this role was hampered by the experimental difficulty of measuring Ca2+ movements through the different compartments of the cell. A major problem was to distinguish the relatively small amount of rapidly exchangeable cellular Ca2+ from the large amount of vascular and interstitial Ca2+. A method that overcomes this problem is reported. Rat hearts were labeled by perfusion at 37.degree. C with medium containing 45Ca2+. They were then cooled, and extracellular 45Ca2+ was removed by perfusion at 6.degree. C with Ca2+-free medium. Cellular 45Ca2+ that was trapped in the hearts by cooling was then released by reperfusion at 37.degree. C with medium containing unlabeled Ca2+. The cellular origin of this 45Ca2+ was confirmed by using [3H]sucrose. When hearts were also labeled with [3H]sucrose, very little [3H]-sucrose was released with the 45Ca2+ peak. The amount of exchangeable cellular Ca2+ in hearts labeled for 5 min was 125 .+-. 13 nmol/g of wet weight. The half-time for its release was < 1 min. This cellular Ca2+ contained at least 2 pools: a rapidly exchanging pool that required extracellular Ca2+ for release (pool A, 38% of total) and a more slowly exchanging pool that did not (pool B, 62% of total). Hearts stimulated with isoproterenol during the 5-min labeling period showed an increase of 46% for the total amount of exchangeable cellular Ca2+; this increase was entirely located in pool A.