Nuutinen M, Hassinen I
Biochim Biophys Acta. 1981 Oct 12;637(3):481-9. doi: 10.1016/0005-2728(81)90054-2.
The role of extracellular Pi and transmembrane fluxes across the sarcolemma in the regulation of cellular respiration was studied in isolated Langendorff-perfused rat hearts. Extracellular phosphate did not significantly affect the oxygen consumption or cellular phosphorylation potential of the myocardium. K+-induced arrest was used to change the mechanical work load of the heart. Arresting the heart caused a rapid decrease in the unidirectional efflux of phosphate determined by in vitro prelabelling of the intracellular phosphate compounds with 32P and determining the specific radioactivity of the gamma-P of ATP, and the label appearance into the perfusion medium. At normal or elevated perfusate phosphate concentration there was a fairly slow net uptake of phosphate. The decrease in phosphate fluxes upon the K+-induced arrest was probably not due to a decrease in the transmembrane Na+ or K+ gradients because a further increase in the perfusate K+ concentration caused an increase in the K+ efflux to the levels observed in contracting hearts. The use of higher than normal concentrations of phosphate necessitated a lowering of the extracellular Ca2+ concentration, which caused a diminution of the oxygen consumption, accompanied by mitochondrial flavoprotein in the heart. This finding suggested that the extracellular Ca2+ concentration may be involved in the substrate level regulation of mitochondrial metabolism.
在离体Langendorff灌注大鼠心脏中研究了细胞外无机磷（Pi）和跨肌膜通量在细胞呼吸调节中的作用。细胞外磷酸盐对心肌的耗氧量或细胞磷酸化电位没有显著影响。用钾离子（K⁺）诱导停搏来改变心脏的机械工作负荷。使心脏停搏导致通过用³²P对细胞内磷酸盐化合物进行体外预标记并测定ATP的γ-P的比放射性以及标记物在灌注培养基中的出现来确定的磷酸盐单向流出迅速减少。在正常或升高的灌注液磷酸盐浓度下，磷酸盐有相当缓慢的净摄取。K⁺诱导停搏后磷酸盐通量的降低可能不是由于跨膜钠（Na⁺）或钾梯度的降低，因为灌注液K⁺浓度的进一步增加导致钾外流增加到在收缩心脏中观察到的水平。使用高于正常浓度的磷酸盐需要降低细胞外钙离子（Ca²⁺）浓度，这导致耗氧量减少，并伴有心脏中的线粒体黄素蛋白。这一发现表明细胞外Ca²⁺浓度可能参与线粒体代谢的底物水平调节。
