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

1.将离体心脏灌注在含有0、1.2或5 mM Pi的Krebs-Henseleit缓冲液中。当Pi从0增加到5 mM时，总[Mg^<2+>]i从17.0减少到16.2mM，而[Pi]i无显著变化。从柠檬酸盐/异柠檬酸盐的比率，对于0、1.2和5 mM Pi，游离[Mg^<2+>]i为0.36、0.44和0.44mM。细胞内pH值分别为6.98、7.19和7.15。随着Pi从0增加到5 mM，[Cl^-]i从51.7下降到11.6mM。[K^+]i在128 - 132 mM之间保持不变，膜电位为-83 mV。[Na在0和5 mM Pi灌注的心脏中，胞浆[SIGMAATP]/[SIGMAADP]/[SIGMAPi]从9，300降至3，360 M ↑ [+]i<-1>。发现对于0、1.2和5 mM Pi的心脏，SIGMATP水解为SIGMAADP和SIGMAPi的自由能为-13.1、-13.3和-13.2Kcal/mole。质膜梯度能量分别为+12.7、+11.3和+13.2Kcal/mole，或细胞磷酸化电位的97%、85%和99%。用细胞磷酸化电位测定大鼠心肌细胞质膜梯度的大小和方向，研究了改变细胞外游离镁对大鼠工作心脏功能和钙含量的影响。随着[Mg ^2 +] o浓度从0增加到2 mM，心肌总[Ca ^2 +] i从0.85下降到0.43mM，[Mg ^2+]i/[Ca^2+]i从22.5上升到53.2。在生理正常的[Mg^&lt;2+&gt;]o为0.5mM时，获得最大心脏效率。

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.