Force-interval relation in normal and cardiomyopathic hamster atria.
The purpose of this study was to determine how cardiomyopathy affects the beat-to-beat regulation of contractile force in cardiac muscle. Isometric force produced by left atria from 80- to 85-day-old normal and cardiomyopathic (CM) hamsters was measured in vitro at 29 degrees C in 2.5 and 6.0 mM Ca2+. During steady-state stimulation at 1 Hz, single test stimuli were interpolated at varying test intervals (0.3-600 s). The force-interval curves were fitted with an equation using five parameters to define the curve and were compared under different conditions; the recovery of force after long rest intervals was fitted with a single exponential curve. Results showed that the force-interval curves were similar in normal and CM atria except that force was depressed at all intervals in 2.5 mM external Ca2+ concentration ([Ca2+]e) and that the parameter U(0), reflecting force produced at short test intervals, tended to be lower in CM muscles. At high [Ca2+]e (6.0 mM) the force-interval curves were similar, but recovery of steady-state force after long test intervals was much slower in CM atria (tau = 77.3 +/- 8.5 s, n = 11) than in normal atria (tau = 30.5 +/- 3.9 s, n = 11). Recovery was also slower at 2.5 mM [Ca2+]e. These findings suggest that, on a beat-to-beat basis, there is less Ca2+ available in intracellular compartments in the CM heart.
Howlett
S E
SE
Department of Pharmacology, University of Alberta, Edmonton, Canada.
Bobet
J
J
Gordon
T
T
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D009202:Cardiomyopathies / Q000503:physiopathology*; D006224:Cricetinae; D006321:Heart / Q000033:anatomy & histology / Q000502:physiology / Q000503:physiopathology*; D006325:Heart Atria; D066298:In Vitro Techniques; D008297:Male; D008647:Mesocricetus; D009200:Myocardial Contraction / Q000187:drug effects; D009929:Organ Size; D012016:Reference Values; D013599:Systole
D002118:Calcium