Na+-dependence of 45Ca2+ uptake in adult rat isolated cardiac cells.
We developed a technique that yields isolated adult rat myocytes, 70% of which are elongated and morphologically similar to intact tissue. Electrophysiological studies showed most of these cells were quiescent, Ca2+-tolerant and exhibited normal action potentials accompanied by contractions. We analyzed 45Ca2+ uptake data in terms of instantaneous, fast and slow compartments. 69% of total exchangeable Ca2+ was found in the slow compartment: the rest was almost equally divided between the instantaneous and fast compartments. Replacement of extracellular Na+ by Li+ or Tris increased 45Ca2+ uptake by the fast compartment; high [K+]o increased this uptake further. These increases appeared to be related also to internal concentrations of Na+. This conclusion was supported by experiments with digitonin-treated cells. Our results indicate that the way Na+-dependent 45Ca2+ uptake is affected by [Na+]o, [Na+]i and [K+]o is compatible with the Na+-Ca2+ exchange mechanism. Our preparation should prove useful in studies of regulation of Ca2+ transport in cardiac muscles.
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002132:Calcium Radioisotopes; D004072:Digitonin / Q000494:pharmacology; D005260:Female; D066298:In Vitro Techniques; D007700:Kinetics; D008854:Microscopy, Electron; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism* / Q000648:ultrastructure; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000494:pharmacology*
D002132:Calcium Radioisotopes; D012964:Sodium; D004072:Digitonin; D002118:Calcium