The effects of intracellular free [Mg^<2+>] as a metabolic regulator on energetics and performance in perfused rat hear

1. 将离体心脏灌注于含有0、1.2或5mM Pi的Krebs-Henseleit缓冲液中。将Pi从0增加到5mM，使总[Mg^<2+>]i从17.0显著降低到16.2mM，但[Pi]i没有显著变化。从柠檬酸盐/异柠檬酸盐比值来看，在0、1.2和5mM Pi下，游离[Mg^<2+>]i分别为0.36、0.44和0.44 mm。胞内pH值分别为6.98、7.19和7.15。当Pi从0增大到5mM时，[Cl^-]i从51.7减小到11.6mM。[K^+]i在128 ~ 132mM范围内不变，膜电位为-83mV， [Na^+]i随Pi的增加分别为1.62、3.68和2.03mM。灌注0和5mM Pi后，胞浆[SIGMAATP]/[SIGMAADP]/[sigmaapi]从9300 M^<-1>降至3360 M^<-1>。在0、1.2和5mM Pi的心脏中，sigmap水解为SIGMAADP和SIGMAPi的自由能分别为-13.1、-13.3和-13.2Kcal/mol。质膜梯度能量分别为+12.7、+11.3和+13.2Kcal/mol，分别占细胞磷酸化电位的97%、85%和99%。通过细胞磷酸化电位测定大鼠心脏内细胞膜梯度的范围和方向。研究了改变细胞外游离Mg对工作大鼠心脏功能和钙含量的影响。当[Mg^<2+>]o从0增加到2mM时，总[Ca^<2+>]i从0.85线性下降到0.43mM, [Mg^<2+>]i/[Ca^<2+>]i从22.5增加到53.2。在[Mg^<2+>] 0条件下，心肌O_2消耗和线粒体[NAD^+]/[NADH]不变。最大心脏效率在生理正常[Mg^<2+>]o为0.5mM时达到。

1. lsolated hearts were perfused in Krebs-Henseleit buffer containing 0, 1.2 or 5mM Pi. lncreasing Pifrom 0 to 5mM significantly decreasedtotal [Mg^<2+>]i from 17.0 to 16.2mM and resulted in no significant change in [Pi]i. From the citrate/isocitrate ratio, free [Mg^<2+>]i was 0.36, 0.44 and 0.44mM for 0, 1.2 and 5mM Pi. The caculated intracellular pH was 6.98, 7.19 and 7.15 respectively. As Pi was increased from 0 to 5mM, [Cl^-]i decreased from 51.7 to 11.6mM.[K^+]i was invariant at 128 to 132mM giving a membrane potential of -83mV.[Na^+]i with increasing Pi was 1.62, 3.68 and 2.03mM.The cytosolic [SIGMAATP]/[SIGMAADP]/[SIGMAPi] decreased from 9,300 to 3,360 M^<-1> in the 0 and 5mM Pi perfused hearts. The free eergy of SIGMATP hydrolysis to SIGMAADP and SIGMAPi was found to be -13.1, -13.3 and -13.2Kcal/mole for 0, 1.2 and 5mM Pi hearts. The energy of the plasma membrane gradients were +12.7, +11.3 and +13.2Kcal/mole, or 97, 85 and 99% of the cellular phosphorylation potential. The extent and direction of the pasma membrane gradients in rat hearts were determined by cellular phosphorylation potential.The effect of changing extracelular free Mg on cardiac function and Ca content was studied in working rat hearts. Total [Ca^<2+>]i decreased linearly from 0.85 to 0.43mM and [Mg^<2+>]i/[Ca^<2+>]i increased from 22.5 to 53.2 as [Mg^<2+>]o increased from 0 to 2mM.Cardiac O_2 consumpton and mitochondrial [NAD^+]/[NADH] were constant in each condition of [Mg^<2+>]o. The maximal cardiac efficiency was attained at a physiologically normal [Mg^<2+>]o of 0.5mM.