Total Ca handling in canine mild Ca overload failing heart

Mohri

et al. 2001

JJP

Self Cite

Myocardial Ca 2ϩ handling in excitation-contraction (E-C) coupling consumes the second largest fraction of myocardial energy (ATP and hence oxygen) next to cross-bridge cycling in a physiologically working heart [1]. To better understand myocardial Ca 2ϩ handling, we have recently developed a new integrative method to quantify total Ca 2ϩ handling in the left ventricle (LV) of the canine beating heart [2][3][4][5][6][7]. This method combines LV myocardial contractility (E max ) and O 2 consumption (VO 2 ) with the internal Ca 2ϩ recirculation fraction (RF). RF is the fraction of total released Ca 2ϩ that is removed by the sarcoplasmic reticulum (SR) without being extruded transsarcolemmally [8][9][10][11].RF has been obtained from the exponential decay beat constant (but not time constant; see METHODS) of the postextrasystolic potentiation (PESP) when it decays monotonically or exponentially [8][9][10][11]. We have demonstrated, however, that PESP most frequently decays in transient alternans, or with the alteration of large and small contraction, in the excised cross-circulated canine heart preparation [12]. We were then able to characterize this transient alternans decay as the sum of an exponential function and an exponentially decaying sinusoidal function [13]. We considered the former decay term to reflect the time course of recovery of intracellular Ca 2ϩ from the transiently augmented level caused by extrasystole to the steady-state level. Therefore RF could be calculated from the beat constant of this decay [2][3][4][5][6][7]. The PESP Key words: myocardial Ca 2ϩ , contractility, arrhythmia, beat constant, extrasystole. Abstract:In our previous studies, we calculated the internal Ca 2ϩ recirculation fraction (RF) after obtaining the beat decay constant ( e ) of the monoexponential component in the postextrasystolic potentiation (PESP) of the alternans decay by curve fitting. However, this method sometimes suffers from the sensitive variation of e with small noises in the measured contractilities of the 5th and 6th postextrasystolic (PES) beats in the tail of the exponential component. We now succeeded in preventing this problem by a new method to calculate RF without obtaining e . The equation for the calculation in the new method expresses an alternans decay of PESP as a recurrence formula of PESP. It can calculate RF directly from the contractilities of the 1st through the 4th PES beats without any fitting procedure. To evaluate the reliability of the new method, we calculated RF from the alternans decay of PESP of the left ventricle (LV) of the canine excised cross-circulated heart preparation by both the original fitting and the new method.Although there was no significant difference in the mean value of the obtained RF between these two methods, the variance of RF was smaller with the new method than with the original method. Thus the new method proved useful and more reliable than the original fitting method.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

See 3 more Smart Citations

New Calculation of Internal Ca2+ Recirculation Fraction from Alternans Decay of Postextrasystolic Potentiation.

Mohri

et al. 2001

JJP

Self Cite

Total Ca²⁺ handling for E-C coupling in the whole heart: An integrative analysis

Mohri

Can. J. Physiol. Pharmacol.

et al. 2001

Self Cite

We assessed total Ca2+ handling (transport, flux) in excitation-contraction (E-C) coupling in a beating left ventricle (LV). We developed a new integrative analysis method that utilizes the internal Ca2+ recirculation fraction (RF), O2 consumption (V(O2)) for Ca2+ handling, and O2 cost of Emax (contractility index) of the LV. We obtained the RF from the beat constant of the exponential decay component of the postextrasystolic potentiation, and the O2 cost of Emax from V(O2) measured at different Emax. Our equation calculated the unknown total Ca2+ handling, futile Ca2+ cycling, and Ca2+ reactivity of Emax from the RF and Ca2+ handling V(O2). The calculated total Ca2+ handling fell between 30 and 110 micromol/kg, depending on Emax and pathological conditions. Our method also allowed an assessment of futile Ca2+ cycling and Ca2+ reactivity of Emax in a beating LV. These data are not available using conventional methods. Our method can be used to better understand the pathophysiology of total Ca2+ handling in a beating heart.

ASSESMENT OF TOTAL CA²⁺ HANDLING FOR EXCITATION-CONTRACTION COUPLING IN BEATING LEFT VENTRICLE

Shimizu

et al. 2001

J. Mech. Med. Biol.

We have aimed to assess total Ca 2+ handling in excitation-contraction coupling in a beating left ventricle (LV). Our newly developed integrative analysis method utilizes the internal Ca 2+ recirculation fraction (RF), O2 consumption ( Vo 2) for Ca2+ handling, and O 2 cost of Emax (contractility index) of the LV. We have obtained the O 2 cost of Emax from Vo 2 measured at different contractility levels, and have combined the cost with RF calculated from the beat-constant of the exponential decay component of the postextrasystolic potentiation. Our method calculates the unknown total Ca2+ handling from the RF and the " Ca 2+ handling Vo 2". The calculated total Ca 2+ handling fell between 30 and 110 μmol/kg, depending on contractility and pathological conditions. The present method also enable's reasonable assessment of futile Ca 2+ cycling and of the Ca 2+ reactivity of Emax. Our method seems useful to better understanding of the pathophysiology of total Ca 2+ handling in a beating heart.