Altered calcium (Ca²⁺) mobilization after burn trauma: Beneficial effects of calcium antagonist dantrolene

Numerous studies have shown that elevated intracellular calcium concentration [Ca²⁺]_i occurs in several cell types after stress related injury. However, the mechanism responsible for the increased [Ca²⁺]_i (that is, altered Ca²⁺ release or uptake from intracellular organelles such as the sarcoplasmic reticulum, SR, versus altered Ca²⁺ influx) remains unclear. This study examined the contribution of SR dysfunction to postburn Ca²⁺ dyshomeostasis in burn injury. Rats were given a 3° burn over 43% TBSA and fluid treated for 24 hours (n=18); sham burns were included for controls (n=19). Hearts were harvested 24 hrs postburn and Ca²⁺ uptake was measured in myocardial homogenates and normalized for protein concentration. Compared to shams, maximal Ca²⁺ uptake capacity (350±10 nmoles/ng protein) and Ca²⁺ uptake velocity (58±2 nmole/mg/min) were reduced after burn trauma (292±15, p<0.01 and 49±1, p<0.01 respectively). In additional studies, burned rats (n=9) received dantrolene a drug which blocks Ca²⁺ release from the SR (10 mg/kg, IV, 30 min, 8 hrs, and 20 hrs postburn); shams received vehicle. Myocytes were isolated (collagenase digestion) 24 hrs postburn. Fura-2 loaded cells (1×10⁵/ml) were excited at wavelengths of 340/380 nm (Hitachi spectrofluorometer) and [Ca²⁺]_i was calculated from fura-2 ratios. Burn trauma increased myocyte [Ca²⁺]_i compared to shams (152±6 vs 307±29 nm, p<0.05); dantrolene reduced the postburn rise in [Ca²⁺] , (164±22 nm, p<0.05). The ability of dantrolene to normalize myocyte [Ca²⁺]_i coupled with abnormalities in SR Ca²⁺ transport suggest that postburn Ca²⁺ dyshomeostasis is related to the defects in up take/release of Ca²⁺ from the SR.