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Calcium displacement by lanthanum in subcellular compartments of rat ventricular myocytes: characterisation by
1Department of Physiology, UCLA 90024-1751.
Objective:
Much of the calcium in cardiac myocytes resides in a kinetic compartment defined by rapid exchange and rapid displacement by La3+. The aim of this study was to ascertain the subcellular location of this calcium pool.
Methods:
Electron probe microanalysis (EPMA) was used to measure redistribution of total calcium in rat cardiac myocytes after 30 s in 1 mM lanthanum. "Cells", mitochondria, and myofibrils were separately analysed. The data permitted calculating a third (difference) compartment, containing primarily sarcoplasmic reticulum, sarcolemma, and T tubule lumen. Total calcium levels in junctional sarcoplasmic reticulum and T tubule lumen were also measured directly.
Results:
Lanthanum decreased total "cell" calcium from 1.4 (SEM 0.3) to 0.5(0.4) mmol.kg-1 dry weight (p < 0.05); loss from the third (difference) compartment was primarily responsible. Simultaneously, junctional sarcoplasmic reticulum increased from 5.1(0.6) to 8.2(0.9) mmol.kg-1 dry weight (p < 0.05), while the T tubule lumen was unchanged.
Conclusions:
These results suggest that lanthanum displaced calcium primarily from sarcolemmal sites and that calcium redistributed to sarcoplasmic reticulum from an intracellular source.