Superior logistic model for decay of Ca2+ transient and isometric relaxation force curve in rabbit and mouse papillary muscles.
A decrease in myocardial intracellular calcium concentration ([Ca(2+)](i)) precedes relaxation, and a monoexponential function is typically used for fitting the decay of the Ca(2+) transient. However, a logistic function has been shown to be a better fit for the relaxation force curve, compared to the conventional monoexponential function. In the present study, we compared the logistic and monoexponential functions for fitting the [Ca(2+)](i) declines, which were measured using the aequorin method, and isometric relaxation force curves at 4 different onsets: the minimum time-derivative of [Ca(2+)](i) (d[Ca(2+)](i)/dt (min)) and force (dF/dt(min)), and the 10%, 20% and 30% lower [Ca(2+)](i) levels and forces over the data-sampling period in 7 isolated rabbit right ventricular and 15 isolated mouse left ventricular papillary muscles. Logistic functions were significantly superior for fitting the [Ca(2+)] (i) declines and relaxation force curves, compared to monoexponential functions. Changes in the normalized logistic [Ca(2+)] (i) decline and relaxation force time constants at the delayed onsets relative to their 100% values at d[Ca(2+)] (i)/dt(min) and dF/dt(min) were significantly smaller than the changes in the normalized monoexponential time constants. The ratio of the logistic relaxation force time constant relative to the logistic [Ca(2+)](i) decline time constant was significantly smaller in mouse than in rabbit. We conclude that the logistic function more reliably characterizes the [Ca(2+)](i) decline and relaxation force curve at any onset, irrespective of animal species. Simultaneous analyses using the logistic model for decay of the Ca(2+) transient and myocardial lusitropism might be a useful strategy for analysis of species-specific myocardial calcium handling.
Mizuno
Ju
J
Department of Anesthesiology, Faculty of Medicine, The University of Tokyo, Japan.
Otsuji
Mikiya
M
Takeda
Kenji
K
Yamada
Yoshitsugu
Y
Arita
Hideko
H
Hanaoka
Kazuo
K
Hirano
Shuta
S
Kusakari
Yoichiro
Y
Kurihara
Satoshi
S
D000465:Algorithms; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D016015:Logistic Models; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009126:Muscle Relaxation / Q000502:physiology*; D053580:Muscle Strength / Q000502:physiology*; D009200:Myocardial Contraction / Q000502:physiology*; D010210:Papillary Muscles / Q000378:metabolism*; D011817:Rabbits; D046509:Tissue Culture Techniques
D002118:Calcium