Calcium affects phosphoinositide turnover in human erythrocytes.
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.
Folk
P
P
Department of Physiology, Charles University, Praha, Czechoslovakia.
Strunecká
A
A
D000001:Calcimycin / Q000494:pharmacology*; D002118:Calcium / Q000494:pharmacology*; D004910:Erythrocyte Membrane / Q000187:drug effects / Q000378:metabolism; D004912:Erythrocytes / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D010712:Phosphatidic Acids / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000097:blood*; D014700:Verapamil / Q000494:pharmacology
D010712:Phosphatidic Acids; D010716:Phosphatidylinositols; D000001:Calcimycin; D014700:Verapamil; D002118:Calcium