title: Intracellular calcium transients in potentiated contractions induced by multiple extrasystolic beats in isolated perfused rat hearts.
abstract: Mechanisms underlying contractile potentiation induced by multiple extrasystolic contractions (ESC) were evaluated with surface fluorometry in isolated perfused rat hearts loaded with Indo-1/AM. After baseline pacing with a 400 ms interval, 1-25 ESC were interposed with a regular 160 ms interval followed by the postextrasystolic beat with a 400 ms interval. With an increase in the ESC number, left ventricular developed pressure and peak positive dP/dt increased in an exponential manner, reaching a plateau, that was the same for 3 extracellular Ca2+ ([Ca2+]o; 0.55 (n = 9), 1.25 (n = 11) and 2.75 mM (n = 7). Increased [Ca2+]o shifted this relationship left and upward, and with 2.75 mM [Ca2+]o developed pressure and dP/dt decreased after the maximum potentiation was obtained. The relationship between the ESC number and the amplitude of the Indo-1 fluorescence (F400/F510; an index of intracellular Ca2+ ([Ca2+]i)) was also exponential and was shifted left and upward by high [Ca2+]o; however, it lacked the declining phase. Thus, the relationship between the amplitude of F400/F510 and developed pressure or dP/dt consisted of a positively linear part until the maximum potentiation was obtained and a negatively linear part with a further increase in the amplitude of F400/F510. This observation suggests that although contractile potentiation is mediated by increased [Ca2+]i transients, the maximum response might be determined by the responsiveness of the sarcomere.
authors.affiliation: Department of Medicine, University of California San Francisco.
authors.forename: S
authors.initials: S
authors.lastname: Kojima
authors.forename: S T
authors.initials: ST
authors.lastname: Wu
authors.forename: J
authors.initials: J
authors.lastname: Wikman-Coffelt
authors.forename: W W
authors.initials: WW
authors.lastname: Parmley
mesh_terms: D000818:Animals; D002118:Calcium / Q000032:analysis*; D005117:Cardiac Complexes, Premature / Q000378:metabolism; D006321:Heart / Q000502:physiology; D007211:Indoles; D009200:Myocardial Contraction / Q000502:physiology*; D009206:Myocardium / Q000378:metabolism*; D010477:Perfusion; D051381:Rats; D017207:Rats, Sprague-Dawley; D012518:Sarcomeres / Q000502:physiology
chemical_list: D007211:Indoles; C048960:indo-1; D002118:Calcium