Folk P, Strunecká A
Department of Physiology, Charles University, Praha, Czechoslovakia.
Gen Physiol Biophys. 1990 Jun;9(3):281-90.
Changes in extracellular Ca2+ concentration ([Ca2+]) were observed to affect 32Pi incorporation into polyphosphoinositides (PPI) and phosphatidic acid (PA) of human erythrocytes. A decrease of extracellular [Ca2+] from 1.5 mmol/l to 0.04 mumol/l increased the specific radioactivity (S.A.) of phosphatidylinositol 4,5-bisphosphate to 182% and that of phosphatidylinositol 4-phosphate to 120% of controls. Simultaneously S.A. and concentration of PA decreased. Further decrease of the extracellular [Ca2+] from 0.04 mumol/l to lower values as well as depletion of intracellular Ca2+ using ionophore A 23187 in Ca2(+)-free medium did not accelerate the PPI turnover rates any more. None of the above changes in extracellular [Ca2+] had any effect on the phosphorylation pattern of erythrocyte membrane proteins. Isolated erythrocyte membranes were incubated in the presence of [gamma-32P]ATP in media with various [Ca2+]. The decrease of [Ca2+] from 0.04 mumol/l (physiological concentration inside the cell) to lower values did not influence the turnover of PPI and PA monoester phosphates. Only after [Ca2+] was increased to 1-5 mumol/l an increase of PPI and PA turnover was observed. Our data suggest that the changes in extracellular [Ca2+] affect the metabolism of PPI and PA (despite the intracellular location of the latter) and may thus influence the properties of red cell plasma membrane.
据观察，细胞外钙离子浓度（[Ca2+]）的变化会影响32Pi掺入人红细胞的多磷酸肌醇（PPI）和磷脂酸（PA）中。细胞外[Ca2+]从1.5 mmol/l降至0.04 μmol/l，使磷脂酰肌醇4,5-二磷酸的比放射性（S.A.）增加至对照的182%，磷脂酰肌醇4-磷酸的比放射性增加至对照的120%。同时，PA的S.A.和浓度降低。细胞外[Ca2+]从0.04 μmol/l进一步降至更低值，以及在无Ca2+的培养基中使用离子载体A 23187耗尽细胞内Ca2+，均不再加速PPI的周转率。上述细胞外[Ca2+]的任何变化对红细胞膜蛋白的磷酸化模式均无影响。将分离的红细胞膜在含有[γ-32P]ATP且[Ca2+]不同的培养基中孵育。[Ca2+]从0.04 μmol/l（细胞内生理浓度）降至更低值，并不影响PPI和PA单酯磷酸的周转率。只有当[Ca2+]增加至1 - 5 μmol/l时，才观察到PPI和PA周转率增加。我们的数据表明，细胞外[Ca2+]的变化会影响PPI和PA的代谢（尽管PA位于细胞内），从而可能影响红细胞质膜的特性。
