J. Biol. Chem., Vol. 265, Issue 14, 8275-8279, 05, 1990
500-Kilodalton calcium sensor regulating cytoplasmic Ca2+ in cytotrophoblast cells of human placenta
C Juhlin, S Lundgren, H Johansson, J Lorentzen, L Rask, E Larsson, J Rastad, G Akerstrom and L Klareskog
Department of Surgery, University of Uppsala, Sweden.
Two monoclonal IgG antibodies E11 and G11, which react with parathyroid and
kidney tubule cells, are in the present communication demonstrated to
immunostain the surface of cytotrophoblast cells in human placenta. The G11
but not the E11 antibody has earlier been found to interfere with the
sensing and gating of extracellular calcium in parathyroid cells.
Microfluorometric measurement of the cytoplasmic calcium (Ca2+i)
concentration was performed on suspended placental cells loaded with
fura-2. The E11-positive placental cells displayed biphasic and
parathyroid-like increases in Ca2+i in response to extracellular Ca2+. This
increase was blocked by the G11 antibody and absent in the E11- negative
placental cells. A sandwich enzyme-linked immunosorbent assay was
constructed in which the G11 and E11 antibodies were shown to react with
the same molecule. This calcium sensor was isolated and found to consist of
a single, glycosylated polypeptide of approximately 500 kDa.