Epidermal growth factor stimulates Ca2+ uptake of human erythrocytes.
To examine the functional significance of epidermal growth factor (EGF) binding sites present on the human erythrocyte membrane [Engelmann et al. (1992) Am J Hematol 39:239-241], the effect of EGF on 45Ca2+ uptake and on 22Na+ efflux from these cells has been studied. In all cases media contained 1.25 mM Ca2+, whereas Na+ and K+ were varied. In 140 mM Na+/5 mM K+ medium EGF (250 ng/ml) stimulated 45Ca2+ uptake by 50%-90% in quin-2-loaded cells, and by up to threefold in untreated cells. Increasing extracellular K+ up to 75 mM at the expense of extracellular Na2+ stimulated the EGF-induced 45Ca2+ uptake by about twofold compared to 145 mM Na+ medium both in quin-2-loaded and in untreated cells. In 145 mM K+ medium, however, no EGF-induced 45Ca2+ uptake was detectable in quin-2-loaded cells, while in untreated cells Ca2+ entry was stimulated twofold by EGF. After increasing intracellular Na+ from 6 mmol/l cells to 18 mmol/l cells in untreated cells suspended in 145 mM K+ medium, 45Ca2+ uptake induced by EGF gradually increased. In contrast, in 140 mM Na+/5 mM K+ as well as in 70 mM Na+/75 mM K+ medium, 45Ca2+ uptake accelerated by EGF was largely unaffected by a modified red cell Na+ content. When 22Na-loaded untreated red cells were suspended in 145 mM K+ medium EGF stimulated red cell 22Na+ efflux by more than threefold. In 140 mM Na+/5 mM K+ as well as in 70 mM Na+/75 mM K+ medium, no 22Na+ efflux induced by the growth factor was evident.(ABSTRACT TRUNCATED AT 250 WORDS)
Engelmann
B
B
Physiologisches Institut der Universität München, Federal Republic of Germany.
Gross
V
V
Schumacher
U
U
Duhm
J
J
D000634:Aminoquinolines; D002118:Calcium / Q000097:blood*; D002132:Calcium Radioisotopes; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D004912:Erythrocytes / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D007474:Ion Exchange; D010042:Ouabain / Q000494:pharmacology; D012964:Sodium / Q000097:blood; D012979:Sodium Radioisotopes; D013268:Stimulation, Chemical
D000634:Aminoquinolines; D002132:Calcium Radioisotopes; D012979:Sodium Radioisotopes; D010042:Ouabain; D004815:Epidermal Growth Factor; D012964:Sodium; C035739:Quin2; D002118:Calcium