Loading of calcium and strontium into the sarcoplasmic reticulum in rat ventricular muscleJournal of Molecular and Cellular Cardiology
AbstractPrevious work suggests that strontium ions (Sr2+) are less effective than calcium ions (Ca2+) at supporting excitation-contraction (EC) coupling in cardiac muscle. We therefore tested whether this was due to differences in the uptake and release of Ca2+ and Sr2+ by the sarcoplasmic reticulum (SR) of rat ventricular trabeculae and myocytes at 22-24Â°C. In permeabilized trabeculae, isometric contractions activated by exposure to Ca2+- and Sr2+-containing solutions produced similar maximal force, but were four times more sensitive to Ca2+ than to Sr2+. The rate of loading and maximal SR capacity for caffeine-releasable Ca2+ and Sr2+ were similar. In isolated, voltage-clamped ventricular myocytes, the SR content was measured as Na+-Ca2+ exchange current during caffeine-induced SR cation releases. The SR Ca2+ load reached a steady maximum during a train of voltage clamp depolarizations. A similar maximal Sr2+ load was not observed, suggesting that the SR capacity for Sr2+ exceeds that for Ca2+. Therefore, the relative inability of Sr2+ to support cardiac EC coupling appears not to be due to failure of the SR to sequester Sr2+. Instead, increases in cytosolic [Sr2+] seem to poorly activate Sr2+ release from the SR. (C) 2000 Academic Press.
Citation InformationC. I. Spencer, Robert J. Barsotti and J. R. Berlin. "Loading of calcium and strontium into the sarcoplasmic reticulum in rat ventricular muscle" Journal of Molecular and Cellular Cardiology Vol. 32 (2000) p. 1285 - 1300
Available at: http://works.bepress.com/robert_barsotti/29/