Gyulai L, Chance B, Ligeti L, McDonald G, Cone J
Department of Psychiatry, Hospital of the University of Pennsylvania, Philadelphia 19104.
Am J Physiol. 1988 May;254(5 Pt 1):C699-708. doi: 10.1152/ajpcell.1988.254.5.C699.
Mitochondrial energy coupling in the gerbil brain was characterized by the relationship between intracellular phosphocreatine (PCr)/inorganic phosphate (Pi), phosphorylation ratio, and the mitochondrial redox state in graded hypoxia. Phosphorus-nuclear magnetic resonance (NMR) spectra of the brain and whole head were taken by surface and saddle coil, respectively. The NADH level of the brain cortex was monitored by in vivo fluororeflectometry. The PCr and Pi of the head and brain did not change between 100 and 10% O2 inhalation. PCr progressively decreased and Pi progressively increased with 6 and 4% 0% inhalation in the head. The PCr/Pi of the brain decreased by 44% at 6% fraction of inhaled oxygen (FIO2) and 57% at 4% FIO2. The ATP level did not change during hypoxia. The calculated phosphorylation ratio of the brain ([PCr] Kck[H+]/[Cr][Pi]) = ([ATP]/[ADP][Pi]) was 4.1 X 10(4) M-1 in normoxia. Hypoxia of increasing severity induced increasing NAD reduction of the brain cortex with 17% NAD reduction at 10% FIO2 when there was no change in phosphorylation ratio. The phosphorylation ratio decreased, i.e., the mitochondria failed to maintain the energy level of the brain when the magnitude of the change in NAD reduction to hypoxia was half of the total redox change between hyperoxia and anoxia. These studies demonstrated the feasibility of combined 31P-NMR and NADH fluorometry measurements on brain in vivo. The observations show similarities between the responses of mitochondrial oxidative phosphorylation to hypoxia in vivo and in vitro.
通过分级低氧条件下细胞内磷酸肌酸（PCr）/无机磷酸（Pi）、磷酸化率与线粒体氧化还原状态之间的关系，对沙鼠脑内的线粒体能量偶联进行了表征。分别使用表面线圈和鞍形线圈获取脑和整个头部的磷核磁共振（NMR）谱。通过体内荧光反射测量法监测大脑皮层的NADH水平。在吸入100%至10%氧气期间，头部和大脑的PCr和Pi没有变化。在头部吸入6%和4%氧气时，PCr逐渐降低，Pi逐渐升高。在吸入氧气分数（FIO2）为6%时，大脑的PCr/Pi降低了44%，在FIO2为4%时降低了57%。在低氧期间ATP水平没有变化。在常氧条件下，计算得出的大脑磷酸化率（[PCr]Kck[H+]/[Cr][Pi]）=（[ATP]/[ADP][Pi]）为4.1×10⁴M⁻¹。随着低氧程度加重，大脑皮层的NAD还原增加，在FIO2为10%时NAD还原增加了17%，此时磷酸化率没有变化。当NAD还原对低氧的变化幅度为高氧和缺氧之间总氧化还原变化的一半时，磷酸化率降低，即线粒体无法维持大脑的能量水平。这些研究证明了在体内对大脑进行³¹P-NMR和NADH荧光测量相结合的可行性。观察结果表明，体内和体外线粒体氧化磷酸化对低氧的反应具有相似性。
