Low [ATP] and elevated [Mg2+] reduce depolarization-induced Ca2+ release in rat skinned skeletal muscle fibres
Low [ATP] and elevated [Mg2+] reduce depolarization-induced Ca2+ release in rat skinned skeletal muscle fibres
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DOI：
10.1111/j.1469-7793.1999.00203.x
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发表时间：
1999-10-01
影响因子：
5.5
通讯作者：
Lamb, GD
中科院分区：
文献类型：
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作者：
Blazev, R;Lamb, GD
1.本研究观察了机械剥皮大鼠骨骼肌纤维[ATP]降低、[Mg~(2+)]升高以及代谢产物AMP和IMP的存在对去极化诱导的肌浆网(SR)钙离子释放的影响。在规定的条件下，用2 mM的游离EGTA螯合释放的钙离子，根据去极化后肌浆网钙离子耗竭的程度来确定钙离子的释放量。在总ATP浓度为8 mM、游离镁离子浓度为1 mM的情况下，肌浆网钙离子多数可被S去极化(2-3 mM)所释放。在相同纤维中的配对比较显示，将[Mg~(2+)]从1 mm增加到3 mm时，单个去极化释放的钙离子总量减少了约40%。当镁离子浓度为1 mM时，将[ATP]降低至0.5 mM并未引起钙离子释放总量的明显变化，但当镁离子浓度为3 mM时，降低[ATP]至0.5 mM会导致钙离子释放总量进一步减少(类似于20%)。在1 mM的镁离子和0.5 mM的ATP作用下，单独加入3 mM的BMP或3 mM的AMP加3 mMR的IMP均不能引起细胞内钙离子释放的显著变化。此外，当镁离子浓度为1 mM时，将[ATP]从8 mM降至0.5 mM，同时加入3 mW AMP和3 mM IMP的联合作用对总钙释放无明显影响。然而，当3mM的镁离子和0.5mM的三磷酸腺苷(相当于50%)已经减少了钙离子的释放时，加入3 mM的AMP和3 mM的IMP可使钙离子的释放量进一步减少2倍。这些结果表明，哺乳动物肌肉纤维去极化诱导的钙释放受ATP及其代谢产物的浓度和游离[Mg2+]的调节。因此，长时间运动后肌肉纤维中钙释放的(可逆性)减少不仅可能是由于[Mg2+]升高，还可能是由于钙释放通道附近局部[ATP]的严重减少，伴随着AMP和IMP的积累进一步加剧了这种影响。
1. This study examined whether reduced [ATP], raised [Mg2+] and the presence of the metabolites AMP and inosine monophosphate (IMP) affected depolarization-induced Ca2+ release from the sarcoplasmic reticulum (SR) in mechanically skinned skeletal muscle fibres of the rat. The amount of Ca2+ released was determined from the extent of SR Ca2+ depletion following a depolarization in the specified conditions with 2 mM free EGTA present to chelate released Ca2+.2. In the presence of 8 mM total ATP and 1 mM free Mg2+, most of the SR Ca2+ could be released by a single (2-3 s) depolarization. Paired comparisons in the same fibres showed that raising the [Mg2+] from 1 to 3 mM reduced the total amount of Ca2+ released by a single depolarization by similar to 40%. At 1 mnr Mg2+, lowering the [ATP] to 0.5 mM did not cause a detectable change in the total amount of Ca2+ released, but when the release rate was reduced by the presence of 3 mM Mg2+, lowering the [ATP] to 0.5 mM resulted in a further (similar to 20 %) reduction in the total amount of Ca2+ released.3. At 1 mM Mg2+ and 0.5 mnr ATP, neither the presence of 3 mM BMP alone nor 3 mM AMP plus 3 mnr IMP caused a significant change in total Ca2+ release. Furthermore, at 1 mM Mg2+ the combined effect of lowering the [ATP] from 8 to 0.5 mM and simultaneously adding 3 mw AMP and 3 mM IMP did not significantly alter total Ca2+ release. However, when Ca2+ release was already reduced by the presence of 3 mnr Mg2+ and 0.5 mnr ATP (to similar to 50%), addition of 3 mM AMP and 3 mM IMP significantly reduced the amount of Ca2+ released a further 2-fold.4. These results show that depolarization-induced Ca2+ release in mammalian muscle fibres is modulated by the concentration of ATP and its metabolic products, as well as by the free [Mg2+]. Consequently, the (reversible) reduction in Ca2+ release occurring in a muscle fibre after prolonged exercise could result not only from raised [Mg2+] but also from a severe reduction in [ATP] locally near the Ca2+ release channels, with the accompanying build-up of AMP and IMP further exacerbating this effect.