ACTIVE TRANSPORT OF ION AND SUBSTRATE IN ISOLATED CELLS AND REGULATION MECHANISM OF ENERGY METABOLISM.

在不同激素激动剂存在的情况下，研究了咖啡因对大鼠肝细胞糖异生和尿异生的影响。10&lt；Micro；M苯肾上腺素可刺激4 mM谷氨酰胺的糖异生和尿素合成，分别是对照组的1.7倍和1.9倍。加入不同浓度的咖啡因和10&lt；Micro&gt；M苯肾上腺素可产生依赖于其浓度的双相效应，即刺激(&lt；10^(-4)&gt；-lt；10^(-3)&gt；M)和抑制(>5 mM咖啡因)。咖啡因浓度为1 mM时，可促进糖异生和尿素合成，分别是对照组的2.1倍和2.4倍。咖啡因的作用取决于苯肾上腺素的作用。不含苯肾上腺素的咖啡因不影响这两种合成。咖啡因的作用需要细胞外的&lt；Ca^(2+)&gt；存在，在没有细胞外&lt；Ca^(2+)&gt；的情况下观察不到咖啡因的作用。在无细胞外的情况下，苯肾上腺素对这两种合成的刺激作用也被消除。咖啡因使呼吸频率增加13%，表明咖啡因增加尿素合成和糖异生所需的ATP总量为1.73；微克/分/克湿重。这一数值相当于苯肾上腺素和咖啡因引起的总摄氧量增加所产生的总ATP的44%。在所有这些条件下，磷酸化电位都是恒定的，1.7x&lt；10^3&gt；-2.4x&lt；10^3&gt；葡萄糖和尿素合成的两条途径都有平等的途径获得细胞的ATP供应，因为这两种合成显示出非常相似的模式。咖啡因对线粒体内氧化还原状态和细胞色素c氧化还原状态的影响更大。

Effects of caffeine on gluconeogenesis and ureagenesis of rat isolated hepatocyte were investigated in the presence of various hormonal agonists. Gluconeogenesis and urea synthesis from 4 mM glutamine were stimulated 1.7 fold and 1.9 fold (compared to control) by 10 <micro> M phenylephrine, respectively. The addition of caffeine at various concentrations with 10 <micro> M phenylephrine induced biphasic effects depending its concentration, i.e., stimulation ( <10^(-4)> - <10^(-3)> M), and inhibition (above 5 mM caffeine). Caffeine at 1 mM stimulated gluconeogenesis and urea synthesis 2.1 fold and 2.4 fold. Effects of caffeine were dependent upon the action of phenylephrine. Caffeine without phenylephrine did not affect both syntheses. Effects of caffeine required the presence of extracellular <Ca^(2+)> , and were not observed in the absence of extracellular <Ca^(2+)> . The stimulations of both syntheses by phenylephrine were also eliminated in the absence of extracellular <Ca^(2+)> .The respiratory rate was enhanced by 13 % by caffeine, indicating that the combined ATP requirement for the increase in urea synthesis and gluconeogenesis caused by caffeine is 1.73 <micro> mol/min/g wet weight. This value corresponded 44 % of total ATP produced by enhanced total oxygen uptake caused by phenylephrine and caffeine. The phosphorylation potentials were constant, 1.7 x <10^3> - 2.4 x <10^3> <M^(-1)> under all of these conditions. The two pathways of glucose and urea syntheses have equal access to the cellular ATP supply, since both syntheses showed very similar patterns. Intramitochondrial and cytochrome c redox state were more reduced by caffeine.