Changes in calcium cycling precede cardiac dysfunction during autoimmune myocarditis in mice

Myocardial inflammation contributes to the development of dilated cardiomyo pathy, as well as other cardiac diseases, We have previously shown decrease d left ventricular function in mice with autoimmune myocarditis. To test th e hypothesis that decreased function is mediated by changes in contractilit y and/or Ca2+ cycling, we isolated cardiac myocytes from mice with myocardi lis and age-matched controls at two time points: day 18 (prior to cardiac d ysfunction) and day 35 (during cardiac dysfunction). We measured cell short ening and the Ca2+ transient simultaneously at 28 degreesC and 0.3 Hz. We a lso quantified proteins which regulate contractility and [Ca2+](i), using W estern blot analysis. Results showed no change in cell shortening or systol ic Ca2+ on day 18, despite a significant reduction in diastolic Ca2+. By da y 35, the decrease in diastolic Ca2+ was accompanied by significantly reduc ed cell shortening and a decrease in the systolic Ca2+ transient. Protein l evels of the sarcoplasmic reticulum Ca2+ ATPase were unchanged at bell time points, while phospholamban and the sodium/calcium exchanger were signific antly reduced in myosin-immunized mice at both time points. Calsequestrin w as unchanged at day 18, but was significantly reduced in the myosin-immuniz ed mice on day 35. Results of this study suggest that decreased diastolic C a2+, as well as protein levels of phospholamban and the sodium/calcium exch anger, may actually contribute to disease progression in autoimmune myocard itis, while changes in calsequestrin may be related to systolic dysfunction in tills model. (C) 2001 Academic Press.