Role of troponin I isoform switching in determining the pH sensitivity of Ca(2+) regulation in developing rabbit cardiac muscle

• Published in: Biochemical and biophysical research communications Vol. 267; no. 3; pp. 912 - 917
• Main Authors: Morimoto, S, Goto, T
• Format: Journal Article
• Language: English
• Published: United States 27.01.2000
• Subjects: Aging - physiology; Animals; Animals, Newborn; Calcium - metabolism; Gene Expression Regulation, Developmental; Gestational Age; Heart - embryology; Heart - growth & development; Heart - physiology; Heart Ventricles; Hydrogen-Ion Concentration; Muscle Fibers, Skeletal - physiology; Muscle, Skeletal - physiology; Myocardial Contraction; Myocardium - metabolism; Protein Isoforms - genetics; Protein Isoforms - metabolism; Rabbits; Troponin I - genetics; Troponin I - metabolism
• ISSN: 0006-291X
• DOI: 10.1006/bbrc.1999.2068

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.