Superior Logistic Model for Decay of Ca2+ Transient and Isometric Relaxation Force Curve in Rabbit and Mouse Papillary Muscles

Abstract

SUMMARYA 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 ] 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. (Int Heart J 2007; 48: 215-232)

Half-logistic time constant: a more reliable lusitropic index than monoexponential time constant regardless of temperature in canine left ventricle

“…Furthermore, we have shown that the decay for myocardial Ca 2+ transient at 30 8C also shows the half-logistic characterization (Mizuno et al 2007). Computer simulation of Ca 2+ handling and CB kinetics has also shown that the cumulative CB detachment curve is reasonably fit by the logistic function (Sakamoto et al 1996).…”

Characterization of Intracellular Ca2+ Transient by the Hybrid Logistic Function in Aequorin-Injected Rabbit and Mouse Papillary Muscles

“…For example, τ E for the CaT decline curve in mouse myocytes is reported to be lower than that in rabbit myocytes [29]. We have also found that τ L and τ E for the CaT decline curve in mouse are smaller than those in rabbit [35]. In the mouse myocyte, the peak increase in L-type Ca 2+ current is smaller, and the SR Ca 2+ content, SR Ca 2+ -ATPase activity, and outward Na + -Ca 2+ exchanger current are greater than in the rabbit myocyte [28,29].…”

“…It has recently been shown, however, that the half-logistic function fits the falling phase of CaT more precisely than the mono-exponential function does [35]. Thus the half-logistic time constant (τ L ) may be superior as an index of velocity to the conventional mono-exponential time constant (τ E ) [35]. Similarly, we suppose that the half-logistic function could fit the rising phase of CaT from the beginning of twitch stimulation to dCa/dt max more precisely than the mono-exponential function.…”

“…It should also be pointed out that some investigators have expressed the falling part of CaTs from dCa/dt min to the end point using mono-exponential [24][25][26][27][28][29][30][31][32] and double mono-exponential functions [33,34]. It has recently been shown, however, that the half-logistic function fits the falling phase of CaT more precisely than the mono-exponential function does [35]. Thus the half-logistic time constant (τ L ) may be superior as an index of velocity to the conventional mono-exponential time constant (τ E ) [35].…”

Calcium-induced calcium release from the sarcoplasmic reticulum can be evaluated with a half-logistic function model in aequorin-injected cardiac muscles

“…The experimental procedures have been previously described in detail [4,6,7]. In short, seven albino rabbits (Japan White; body weight 2.0-2.5 kg) and 15 mice (C57BL/6; body weight 25-30 g) were anesthetized with intravenous (1.5-2.0 mg/kg) and intraperitoneal (15-20 mg/kg) pentobarbital sodium, respectively.…”