Calcium displacement by lanthanum in subcellular compartments of rat ventricular myocytes: characterisation by electron probe microanalysis.
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.[1]References
- Calcium displacement by lanthanum in subcellular compartments of rat ventricular myocytes: characterisation by electron probe microanalysis. Miller, T.W., Tormey, J.M. Cardiovasc. Res. (1993) [Pubmed]
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