Some factors which influence the amount of calcium stored at the superficially located sites in cardiac muscle cells
Nayler, W.G.
Recent Advances in Studies on Cardiac Structure and Metabolism 5: 73-79
1975
ISSN/ISBN: 0363-5872 PMID: 1188177 Document Number: 84810
The cell membranes of cardiac muscle cells are impermeable to the trivalent rare earth element, lanthanum (La3+). Because La3+ displaces Ca2+ from its binding sites and because it does not penetrate across the cell membrane, it can be used to determine how much Ca2+ is stored at these superficially located sites. Using this technique it has been possible to study the various factors which influence the Ca2+ storing capacity of these superficially located sites. Substitution of Cl- by NO3- and Br- in the bathing fluid, and prolonged periods of perfusion reduce, whereas hyperthyroidism, an increase in the extracellular concentration of Ca2+, and a reduction in the extracellular concentration of Na+ increase the amount of Ca2+ stored at these superficially located sites. Some drugs which are negatively inotropic (verapamil and pentobarbitone) reduce, whereas others, which are positively inotropic (ouabain), increase the amount of Ca2+ which is available for displacement by La3+. Ca2+ which is stored at these sites plays an important role in regulating cardiac contractility.