Sulfate self-exchange and amino acid transport in calcium-loaded human erythrocytes.
To analyze the effects of Ca2(+)-mediated membrane protein changes on the membrane function, we have studied the SO4(2-) self-exchange and amino acid transport in human erythrocytes after loading them with Ca2+ with the help of ionophore A23187. The SO4(2-) self-exchange is inhibited by 20-30% by loading the erythrocytes with 25 microM to 0.5 mM Ca2+. The extent of this inhibition is almost doubled (50-60%) by increasing the Ca2+ loading concentration to 1.5 mM. This additional effect of 1.5 mM Ca2+ is not correlated with the Ca2(+)-induced ATP depletion or membrane protein degradation, but is caused by the transglutaminase-catalyzed membrane protein crosslinking. Like the SO4(2-) self-exchange, L-alanine and L-cysteine uptakes are also inhibited in Ca2(+)-loaded cells. However, no effect is observed on the L-lysine uptake under identical conditions. These results have been interpreted to suggest that the Ca2(+)-mediated effects on the SO4(2-) self-exchange and amino acid transport are caused perhaps by the Ca2(+)-induced structural rearrangement of the band 3 protein.
Joshi
R
R
Division of Membrane Biology, Central Drug Research Institute, Lucknow, India.
Gupta
C M
CM
D000255:Adenosine Triphosphate / Q000378:metabolism; D000596:Amino Acids / Q000097:blood*; D001457:Anion Exchange Protein 1, Erythrocyte / Q000378:metabolism*; D001692:Biological Transport; D000001:Calcimycin / Q000378:metabolism; D002118:Calcium / Q000097:blood*; D003538:Cystamine / Q000494:pharmacology; D004912:Erythrocytes / Q000378:metabolism*; D006801:Humans; D007474:Ion Exchange; D007700:Kinetics; D013431:Sulfates / Q000097:blood*; D011503:Transglutaminases / Q000378:metabolism
D000596:Amino Acids; D001457:Anion Exchange Protein 1, Erythrocyte; D013431:Sulfates; D000001:Calcimycin; D000255:Adenosine Triphosphate; D011503:Transglutaminases; D003538:Cystamine; D002118:Calcium