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Thermal injury alters myocardial sarcoplasmic reticulum calcium channel function
J T Murphy1, B Giroir, J W Horton
1Department of Surgery, University of Texas Southwestern Medical Center, Dallas, Texas, 75235, USA.
Background:
We have previously shown that a major cutaneous thermal injury produces profound cardiac contractile dysfunction despite adequate resuscitation. While the molecular basis of this dysfunction is unknown, recent work has suggested that alterations in calcium flux between the myocyte sarcoplasmic reticulum (SR) to the cytoplasm may play a role.
Materials And Methods:
To determine if thermal injury-induced contractile dysfunction is related to intracellular calcium transport across the SR membrane, we accessed myocardial microsomal preparations from scalded (43% TBSA) guinea pigs for the ability of the cardiac calcium efflux channel to bind radiolabeled ryanodine. Intracellular calcium flux was assessed by fluorescence spectrophotometry.
Results:
Thermal injury resulted in severe cardiac contractile deficit characterized by loss of LVP and +/-dP/dt despite resuscitation. Analysis of isolated myocyte cultures showed a twofold increase in cytoplasmic [Ca2+]l by 24 h postburn. Competitive binding and Scatchard analysis demonstrated a single, high-affinity binding site present in both sham and burn animal hearts. Myocardial membrane vesicles revealed a significantly enhanced number of calcium efflux channels in the open configuration at both 8 and 24 h following thermal injury compared to time-matched shams (1.07 +/- 0.01 and 0.95 +/- 0.06 vs 0.85 +/- 0.01 pmol bound/mg protein, P < 0.05). The data indicate that altered function of the myocardial transmembrane SR calcium efflux channel following thermal injury was associated with elevated [Ca2+]l and contractile dysfunction.
Conclusions:
We conclude that postburn cardiac dysfunction may partly be a result of elevated cytoplasmic calcium concentrations and diminished regulation of SR calcium efflux channel activity.
Insights
Major burns cause heart dysfunction due to altered calcium handling. Increased cytoplasmic calcium and impaired sarcoplasmic reticulum (SR) calcium efflux channels contribute to this postburn cardiac issue.
Area of Science:
- Cardiology
- Physiology
- Burn Injury Research
Background:
- Major cutaneous thermal injury leads to significant cardiac contractile dysfunction, even with adequate resuscitation.
- The molecular mechanisms underlying this postburn cardiac dysfunction remain unclear.
- Altered calcium flux from the sarcoplasmic reticulum (SR) to the cytoplasm is a potential contributor.
Purpose of the Study:
- To investigate the relationship between thermal injury-induced cardiac dysfunction and intracellular calcium transport across the SR membrane.
- To determine if altered SR calcium efflux channel activity is involved in postburn cardiac dysfunction.
Main Methods:
- Myocardial microsomal preparations from scalded guinea pigs were used to assess cardiac calcium efflux channel binding of radiolabeled ryanodine.
- Intracellular calcium flux was measured using fluorescence spectrophotometry.
- Analysis included competitive binding and Scatchard analysis on myocardial membrane vesicles.
Main Results:
- Thermal injury caused severe cardiac contractile deficit, evidenced by loss of left ventricular pressure (LVP) and +/-dP/dt.
- Cytoplasmic calcium ([Ca2+]l) levels doubled by 24 hours postburn.
- A significantly increased number of calcium efflux channels were observed in the open configuration following thermal injury.
Conclusions:
- Postburn cardiac dysfunction is partly attributed to elevated cytoplasmic calcium concentrations.
- Diminished regulation of SR calcium efflux channel activity contributes to cardiac dysfunction after thermal injury.