title: Effects of Ca2+ on erythrocyte membrane skeleton-bound phosphofructokinase, ATP levels, and hemolysis.
abstract: Erythrocyte Ca2+ overload is known to occur in several different disease states, and to affect the erythrocyte membrane deformability. We show here that an increase in intracellular Ca2+ concentration in erythrocytes, induced by ionomycin, caused a reduction in ATP levels. Concomitant to the fall in ATP, a marked activation of phosphofructokinase (PFK) (EC 2.7.1.11), the rate-limiting enzyme in glycolysis, in the membrane skeleton fraction occurred. The increase in the membrane skeleton-bound PFK activity was most probably mediated by Ca2+, as direct addition of Ca2+ to the membrane skeleton fraction from the erythrocyte induced an enhancement of the bound PFK activity. Time-response curves revealed that erythrocyte hemolysis did not occur during the first 30 min of incubation with ionomycin, when the membrane skeleton-bound PFK was activated. Longer incubation time resulted in solubilization of the membrane skeleton-bound PFK and a concomitant hemolysis of the erythrocytes. These results suggest that the Ca2+-induced activation of membrane skeleton-bound PFK, and thereby glycolysis, the sole source of energy in erythrocytes, may be a defense mechanism to surmount the damage induced by high Ca2+ levels.
authors.affiliation: Department of Life Sciences, Bar-Ilan University, Ramat Gan, 52900, Israel.
authors.forename: M
authors.initials: M
authors.lastname: Assouline-Cohen
authors.forename: R
authors.initials: R
authors.lastname: Beitner
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004910:Erythrocyte Membrane / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D004912:Erythrocytes / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D006461:Hemolysis / Q000187:drug effects*; D015759:Ionomycin / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D008297:Male; D010732:Phosphofructokinase-1 / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D013997:Time Factors