Half-Logistic Function Model for First Half of Descending Phase of Cardiomyocyte Cytoplasmic Ca^(2+) Concentration ([Ca^(2+)]_i)-Time Curve (CaTCIII) in Isolated Aequorin-Injected Mouse Left Ventricular Papillary Muscle

• Published in: Acta Cardiologica Sinica Vol. 32; no. 1; pp. 65 - 74
• Main Authors: Mizuno, Ju, Otsuji, Mikiya, Yokoyama, Takeshi, Arita, Hideko, Hanaoka, Kazuo
• Format: Journal Article
• Language: English
• Published: China (Republic : 1949- ) 中華民國心臟學會 01-01-2016
• Subjects: Half-logistic non-zero asymptote; Ca^(2+) transient; Half-logistic amplitude constant; Half-logistic time constant; Myocardial Ca^(2+) handling
• DOI: 10.6515/ACS20150424G
• ISSN: 1011-6842

Myocardial contraction and relaxation are regulated by increases and decreases in cytoplasmic calcium concentration ([Ca(2+)]i). In previous studies, we found that a half-logistic (h-L) function, which represents a half-curve of a symmetrical sigmoid logistic function with a boundary at the inflection point, curve-fits the first half of the ascending phase and the second half of the descending phase of the [Ca(2+)]i transient curve better than a mono-exponential (m-E) function. In the present study, we investigated the potential application of an h-L function to analyse the first half of the descending phase of CaTC (CaTCIII).
The [Ca(2+)]i was measured using the Ca(2+)-sensitive aequorin, which was microinjected into 15 isolated mouse left ventricular (LV) papillary muscles. The observed CaTCIII data in the interval from the point corresponding to the peak [Ca(2+)]i to the point corresponding to dCa/dtmin was curve-fitted using the h-L and m-E function equations by the least-squares method.
The mean correlation coefficient (r) values of the h-L and m-E function best curve-fits for 11 CaTCIIIs were 0.9986 and 0.9982, respectively. The Z transformation of h-L r (3.64 ± 0.45) was larger than that of m-E r (3.50 ± 0.33) (p < 0.05).
The h-L function can evaluate most CaTCIIIs more accurately than the m-E function in isolated aequorin-injected mouse LV papillary muscle. The three calculated h-L parameters i.e., amplitude constant, time constant, and non-zero asymptote, are more reliable indices than m-E for evaluating the magnitude and time course of the change in the decrease in [Ca(2+)]i.
Ca(2+) transient; Half-logistic amplitude constant; Half-logistic non-zero asymptote; Half-logistic time constant; Myocardial Ca(2+) handling.