Journal of Clinical Endocrinology & Metabolism, Vol 67, 1299-1304, Copyright © 1988 by Endocrine Society

ARTICLES

Epitopes of the human erythrocyte Ca2+-Mg2+ ATPase pump in human osteoblast-like cell plasma membranes

JL Borke, EF Eriksen, J Minami, P Keeting, KG Mann, JT Penniston, BL Riggs and R Kumar
Department of Medicine, Mayo Clinic, Rochester, Minnesota 55905.

Human osteoblast-like cells were examined for the presence of the Ca2+- Mg2+ ATPase pump. The osteoblast-like cells had characteristic features of the osteoblast phenotype, including the presence of osteonectin, bone GLA protein, and type I collagen. The cells were able to mineralize matrix, their production of cAMP increased in response to PTH, and their alkaline phosphatase activity increased in response to 1,25-dihydroxyvitamin D3. Immunocytochemical staining of the osteoblast- like cells with a monoclonal antibody against human red cell Ca2+-Mg2+ ATPase demonstrated the presence of an epitope of the Ca2+-Mg2+ ATPase in these cells; staining of paraffin-embedded osteoblast-like cell sections demonstrated anti-Ca2+-Mg2+ ATPase staining only in cell plasma membranes. Western blot analysis of osteoblast-like cell homogenates showed that the monoclonal antibody to human erythrocyte Ca2+-Mg2+ ATPase bound to a major band at 140,000 mol wt, similar to the mol wt of known plasma membrane Ca2+-Mg2+ ATPases. The presence in the osteoblast-like cells of a Ca2+-Mg2+ ATPase similar to the human red cell calcium pump suggests that this enzyme may play a role in osteoblast intracellular calcium homeostasis.