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Impaired cardiomyocyte relaxation and diastolic function in transgenic mice expressing slow skeletal troponin I in the heart
Author(s) -
Fentzke Richard C.,
Buck Scott H.,
Patel Jitandrakumar R.,
Lin Hua,
Wolska Beata M.,
Stojanovic Miroslav O.,
Martin Anne F.,
Solaro R. John,
Moss Richard L.,
Leiden Jeffrey M.
Publication year - 1999
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1999.0143z.x
Subject(s) - medicine , transgene , isoprenaline , troponin i , genetically modified mouse , intracellular , myocyte , endocrinology , biology , myofibril , troponin , diastole , stimulation , cardiac function curve , heart failure , microbiology and biotechnology , biochemistry , gene , myocardial infarction , blood pressure
1 To assess the specific functions of the cardiac isoform of troponin I (cTnI), we produced transgenic mice that expressed slow skeletal troponin I (ssTnI) specifically in cardiomyocytes. Cardiomyocytes from these mice displayed quantitative replacement of cTnI with transgene‐encoded ssTnI. 2 The ssTnI transgenic mice were viable and fertile and did not display increased mortality or detectable cardiovascular histopathology. They exhibited normal ventricular weights and heart rates. 3 Permeabilized transgenic cardiomyocytes demonstrated an increased Ca 2+ sensitivity of tension and a lack of contractile responsiveness to cAMP‐dependent protein kinase (PKA). Isolated cardiomyocytes from transgenic mice had normal velocities of unloaded shortening but unlike wild‐type controls exhibited no enhancement of the velocity of shortening in response to treatment with isoprenaline. Transgenic cardiomyocytes exhibited greater extents of shortening than non‐transgenic cardiomyocytes at baseline and after treatment with isoprenaline. 4 The rates of rise of intracellular [Ca 2+ ] and the peak amplitudes of the intracellular [Ca 2+ ] transients were similar in transgenic and wild‐type myocytes. However, the half‐time of intracellular [Ca 2+ ] decay was significantly greater in the transgenic myocytes. This change in decay of intracellular [Ca 2+ ] was correlated with an increase in the re‐lengthening time of the transgenic cells. 5 These changes in cardiomyocyte function in vitro were manifested in vivo as impaired diastolic function both at baseline and after stimulation with isoprenaline. 6 Thus, cTnI has important roles in regulating the Ca 2+ sensitivity of cardiac myofibrils and controlling cardiomyocyte relaxation and cardiac diastolic function. cTnI is also required for the normal responsiveness of cardiomyocytes to β‐adrenergic receptor stimulation.