Role of troponin I isoform switching in determining the pH sensitivity of Ca(2+) regulation in developing rabbit cardiac muscle.
Skinned muscle fibers prepared from fetal rabbit heart (28 days of gestation) showed a marked resistance to acidic pH in the Ca(2+) regulation of force generation, compared to the fibers prepared from adult heart. SDS-PAGE and immunoblot analysis showed that the slow skeletal troponin I was predominantly expressed in the fetal cardiac muscle, while the cardiac isoform was predominantly expressed in the adult cardiac muscle. Direct exchange of purified slow skeletal and cardiac troponin I isoforms into these skinned muscle fibers revealed that cardiac troponin I made the Ca(2+) regulation of contraction sensitive to acidic pH just as in the adult fibers, whereas slow skeletal troponin I made the Ca(2+) regulation of contraction resistant to acidic pH just as in the fetal fibers. These results demonstrate that the troponin I isoform switching accounts fully for the change in the pH dependence of Ca(2+) regulation of contraction in developmental cardiac muscle.
Morimoto
S
S
Department of Clinical Pharmacology, Graduate School of Medical Sciences, Kyushu University, Maidashi, Higashi-ku, Fukuoka, 812-8582, Japan. morimoto@clipharm.med.kyushu-u.ac.jp
Goto
T
T
D000375:Aging / Q000502:physiology*; D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D005865:Gestational Age; D006321:Heart / Q000196:embryology / Q000254:growth & development / Q000502:physiology*; D006352:Heart Ventricles; D006863:Hydrogen-Ion Concentration; D018485:Muscle Fibers, Skeletal / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D011817:Rabbits; D019210:Troponin I / Q000235:genetics* / Q000378:metabolism*
D020033:Protein Isoforms; D019210:Troponin I; D002118:Calcium