Increased leakage of sarcoplasmic reticulum Ca2+ contributes to abnormal myocyte Ca2+ handling and shortening in sepsis

Objective: Changes in cardiac function due to sepsis have been widely reported. However, the underlying mechanisms remain poorly understood. In the mammalian heart, myocyte function and intracellular calcium homeostasis are closely coupled. In this study we tested the hypothesis that alterations in cardiac calcium homeostasis due to sepsis underlie the observed myocyte dysfunction. Design: Randomized prospective animal study. Setting. Research laboratory. Subjects: Male Sprague-Dawley rats weighing 250-275 g. Interventions: We induced sepsis by cecal ligation and puncture in the rat, which mimics the type of infection caused by perforation of the intestine in humans. Measurements and Results. Forty-eight hours after cecal ligation and puncture, isolated cardiac ventricular cardiomyocytes demonstrated a 57% decreased peak systolic [Ca2+]. The time constant of the Ca2+ transient increased 71% and 57% in myocytes obtained 24 hrs and 48 hrs after cecal ligation and puncture, respectively. The average shortening of cardiomyocytes 48 hrs after cecal ligation and puncture was significantly decreased. To investigate the cellular mechanisms of altered Ca2+ transients and myocyte shortening, we measured Ca2+ sparks, the spontaneous local Ca2+ release events in cardiomyocytes at resting states. The Ca2+ spark frequency progressively increased in myocytes 24 hrs and 48 hrs after cecal ligation and puncture. The total activity of sparks also increased compared with sham-operated animals. The overall leakage of sarcoplasmic reticulum Ca2+ in resting states was increased in sepsis and resulted in reduced sarcoplasmic reticulum Ca2+ content. Conclusions. Abnormal Ca2+ leakage from the sarcoplasmic reticulum contributes significantly to the depressed myocyte shortening in sepsis. In the future, modalities that prevent this Ca2+ leakage may prove beneficial in the treatment of sepsis induced myocyte shortening.