Isoform Expression in Human Heart

Troponin I is the inhibitory component of troponin, the thin filament regulatory complex in striated muscle. Separate genes encode cardiac-specific fast and slow skeletal-specific isoforms of this protein. We have previously described gene switching from the slow skeletal to the cardiac troponin I mRNA expression in developing rat heart. The purpose of this work was to characterize the expression of the different troponin isoforms in the human heart. Human cardiac and slow skeletal troponin I cDNA probes were obtained by screening an adult cardiac cDNA library and by Taq polymerase amplification ofRNA from an infant's heart, respectively. We found that the cardiac troponin I isoform is tissue-specific in its expression in normal adult tissues. RNA blot analysis of cardiac ventri_ular RNA from infants with congenital heart disease and from an adult with cardiomyopathy revealed expression ofhuman cardiac troponin