title: Calcium-induced calcium release from the sarcoplasmic reticulum can be evaluated with a half-logistic function model in aequorin-injected cardiac muscles.
abstract: OBJECTIVE
  Release of calcium (Ca(2+)) from the sarcoplasmic reticulum (SR) induced by Ca(2+) influx through voltage-dependent sarcolemmal L-type Ca(2+) channels (CICR) in cardiac muscle cells has been implicated as a potential target contributing to anesthetic-induced myocardial depression. In an earlier study, we found that (1) a half-logistic (h-L) function, which represents a half-curve of a sigmoid logistic function with a boundary at the inflection point, curve-fits the first half of the ascending phases of the isometric myocardial tension and isovolumic left ventricular (LV) pressure waveforms better than a mono-exponential (m-E) function and (2) the h-L time constants are useful as inotropic indices. We report here our investigation of the potential application of an h-L function to the analysis of the first half of the ascending phase of the Ca(2+) transient curve (faCaT) that precedes and initiates myocardial contraction and the increase in LV pressure.
  
  
  METHODS
  Ca(2+) transients (CaT) were measured using the Ca(2+)-sensitive photoprotein aequorin, which was microinjected into seven isolated rabbit right ventricular and 15 isolated mouse LV papillary muscles. The faCaT data from the beginning of twitch stimulation to the maximum of the first-order time derivative of Ca(2+) concentration (dCa/dt(max)) was curve-fitted by the least-squares method using h-L and m-E function equations.
  
  
  RESULTS
  The mean correlation coefficient (r) values of the h-L and m-E curve-fits for the faCaTs were 0.9740 and 0.9654 (P < 0.05) in the rabbit and 0.9895 and 0.9812 (P < 0.0001) in the mouse.
  
  
  CONCLUSIONS
  The h-L curves tracked the amplitudes and time courses of the faCaTs in cardiac muscles more accurately than m-E functions. Based on this result, we suggest that the h-L time constant may be a more reliable index than the m-E time constant for evaluating the rate of CICR from the SR in myocardial Ca(2+) handling. The h-L approach may provide a more useful model for the study of CICR during the contraction process induced by anesthetic agents.
authors: Department of Anesthesiology, Faculty of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8655, Japan. mizuno_ju7@yahoo.co.jp
authors: Ju
authors: J
authors: Mizuno
authors: Kazuo
authors: K
authors: Hanaoka
authors: Mikiya
authors: M
authors: Otsuji
authors: Hideko
authors: H
authors: Arita
authors: Hidetoshi
authors: H
authors: Sakamoto
authors: Satoru
authors: S
authors: Fukuda
authors: Shigehito
authors: S
authors: Sawamura
mesh_terms: D000331:Aequorin / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D009202:Cardiomyopathies / Q000139:chemically induced / Q000378:metabolism / Q000503:physiopathology; D006352:Heart Ventricles / Q000187:drug effects / Q000378:metabolism; D066298:In Vitro Techniques; D016015:Logistic Models; D051379:Mice; D008810:Mice, Inbred C57BL; D009200:Myocardial Contraction / Q000187:drug effects / Q000502:physiology; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D010210:Papillary Muscles / Q000187:drug effects* / Q000378:metabolism* / Q000502:physiology; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D016277:Ventricular Function, Left / Q000187:drug effects / Q000502:physiology
chemical_list: D000331:Aequorin; D002118:Calcium