title: The effect of stimulation frequency and calcium concentration on maintenance of developed tension in isolated heart muscle preparations.
abstract: The ability of isolated cardiac muscle preparations to maintain force of contraction was assessed at different extracellular Ca2+ concentrations and at various stimulation frequencies. Preparations were incubated in Krebs-Henseleit buffer at 32 degrees C and electrically stimulated at frequencies between 0.25 and 3.0 Hz. Extra-cellular Ca2+ was maintained at given concentrations between 0.8 and 2.4 mM, a range that included the plasma-ionized Ca2+ levels determined for rat and guinea pig. Developed tension of atrial or papillary muscle preparations of guinea pig heart was more stable at higher stimulation frequencies. Rat atria and ventricular strips were more stable at 0.25 than at 0.5 or 1.0 Hz, and the stability increased at 2.0 and 3.0 Hz. Guinea pig atrial muscle was maintained for a longer time at higher media Ca2+ concentrations; however, no such effect was observed with rat atrial tissue. Thus, the decrementing at developed tension in isolated cardiac muscle preparations is dependent on stimulation frequency and Ca2+ concentrations and can be retarded by selection of appropriate incubation conditions.
mesh_terms: D000818:Animals; D002118:Calcium / Q000097:blood / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D002118:Calcium