Developmental changes in the expression of rabbit left ventricular troponin T

We examined cardiac troponin T (TnT) isoform expression in rabbit left ventricular myocardium at three different stages of postnatal development. Using sodium dodecyl sulfate gel electrophoresis (PAGE), we resolved five isoforms: TnT1, TnT2, TnT3, TnT4, and TnT5. TnT1 had the slowest electrophoretic mobility and TnT5 the fastest. The predominant isoforms were TnT2, TnT3, and TnT4. The relative amounts of TnT2, TnT3, TnT4, and TnT5 were examined in myocardium from three age-groups: 3 days (Group 1), 21-22 days (Group 2), and 99-109 days (Group 3). The amount of TnT2 relative to the total amount of TnT (determined by the ratio of the areas under the densitometric curves) decreased significantly (p less than 0.01) with age from 42 +/- 4% in Group 1 to 25 +/- 3% in Group 3. In contrast, the relative amount of TnT4 increased with age from 23 +/- 2% in Group 1 to 33 +/- 4% in Group 3 (p less than 0.01). The relative amounts of the other two isoforms change biphasically with development: TnT3 decreased from Group 1 to Group 2 and increased from Group 2 to Group 3. TnT5, a minor isoform, increased from Group 1 to Group 2 and decreased from Group 2 to Group 3. These developmental changes in troponin T expression may account for some of the maturational changes observed in the physiological and biochemical properties of the myocardium.