PLASMA-MEMBRANE CALCIUM-ATPASE IN CULTURED HUMAN RETINAL-PIGMENT EPITHELIUM

The present work demonstrates the presence of plasma membrane (Ca2+ Mg2+)-ATPase (PMCA) activity in cultured human retinal pigment epithel ium (HRPE). Whole-cell HRPE homogenates exhibited Ca2+-stimulated ATPa se activity that was inhibited with high affinity (IC50 = 60 nM) by eo sin, a potent inhibitor of the erythrocyte PMCA. This activity was not inhibited by thapsigargin, a selective inhibitor of the sarcoplasmic/ endoplasmic reticulum Ca2+-ATPase (SERCA). A PMCA-specific monoclonal antibody exhibited staining in attached HRPE monolayers. By Western bl ot analysis of SDS-PAGE separations of whole cell lysates of HRPE, thi s antibody identified a single band at similar to 145 kD. Finally, a C a2+-dependent, La3+-augmented phosphoprotein, which comigrated with an ti-PMCA immunoreactivity, was also detected. Taken together, these res ults show that cultured HRPE express PMCA activity. (C) 1996 Academic Press Limited