抄録
In Langendorff perfused rat heart, pressure development decrease to the infra-basal level by the washout of isoproterenol (iso). Since it has been reported that iso decreases intracellular Mg concentration, we hypothesized that iso washout-induced decrease in cardiac contractility is induced by the decrease of intracellular Mg concentration. We examined the relationship between cardiac contractility and Mg content in the hearts by using Langendorff perfused rat heart model and atomic absorption spectrophotometry. Application of iso (10 nM, 15 min) caused positive chronotropic and inotropic effects. After washout of iso (30 min), heart rate (HR) recovered to basal level, but left ventricular developed pressure (LVDP) decreased to significantly lower level than that of time matched control (70.7 ± 3.9 vs 88.9 ± 7.1%, respectively; p<0.05). When iso was applied with high Mg (12 mM; iso + high Mg group), iso washout-induced deterioration of LVDP was significantly inhibited (86.9 ± 4.0%, p<0.05 vs iso group). When extracellular Ca concentration was decreased, to mimic the Ca blocking effect of Mg, iso washout-induced decrease in contractility was not affected. Intracellular Mg content decreased from 739.2 ± 15.2 (control group) to 721.6 ± 25.5 μg/g dry (iso group), but in iso + high Mg group, Mg content was kept at high level (762.3 ± 36.2 μg/g dry). These results suggest that intracellular Mg may play an important role to maintain the cardiac contractility. [J Physiol Sci. 2007;57 Suppl:S204]
