We tested the hypothesis that altered myofilament function contributes to postcardioplegic dysfunction. Left ventricular developed pressure (LVDevP) was measured in isolated perfused (Krebs-Ringer's bicarbonate buffer), non-ejecting (isovolumic) rat hearts. After a 30 min equilibration period (preload pressure set at 5-10 mmHg), hearts were perfused for another 60 min, or with 4°C K+ cardioplegic solution (St. Thomas #2; 1.5ml every 15 min for 120 min), followed by a 60 min reperfusion period. Hearts were freeze clamped at the end of 30 (control;CON; n=8) or 90 min perfusion (TCON; n=7), the end of the cardioplegic period (CPL; n=9), or the end of reperfusion (RPR; n=7) for later determination of myofibrillar ATPase activity at pCa 8.0-4.5. Data (x̄ ± SEM; Table) were analyzed using ANOVA (p<0.05). There were no significant differences between 30 min equilibration LVDevP values for CON, TCON, CPL, or RPR hearts. After 120 min of cardioplegia and 60 min reperfusion LVDevP was reduced 45 ± 12% in RPR hearts, but not in TCON hearts. Minimum and maximal myofibrillar ATPase activities were not affected. In CPL and RPR hearts the Hill coefficient decreased, suggesting a decrease in the cooperative myofilament activation prior to reperfusion. In contrast, the pCa50 (Ca+2 concentration providing half-maximal ATPase response) was not significantly increased in CPL or RPR myofibrils, indicating no change in the sensitivity to calcium. These data suggest that detrimental changes occur in myofibrillar function as a result of cardioplegic procedures alone, as well as with reperfusion. These changes would contribute to incomplete systolic and diastolic ventricular recovery after cardioplegic procedures. CON TCON CPL RPR Hill 2.16±0.2 2.28±0.1 1.71±0.2*2.02±0.2*pCa50, 6.02±0.1 6.11±0.03 6.09±0.1 6.19±0.1 Funding for this work was provided by a Veterans Administration Merit Review grant.
|Original language||English (US)|
|State||Published - Dec 1 1997|
ASJC Scopus subject areas
- Agricultural and Biological Sciences (miscellaneous)
- Biochemistry, Genetics and Molecular Biology(all)
- Cell Biology