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Parathyroid-like regulation of parathyroid-hormone-related protein release and cytoplasmic calcium in cytotrophoblast cells of human placenta

1992; Elsevier BV; Volume: 293; Issue: 1 Linguagem: Inglês

10.1016/0003-9861(92)90381-6

1096-0384

Per Hellman, Peter Ridefelt, Claes Juhlin, Göran Åkerström, Jonas Rastad, Erik Gylfe,

Parathyroid Disorders and Treatments

Immunohistochemical staining of human placenta revealed intense reactivity for amino terminal and midregional parathyroid-hormone-related protein (PTHrp) in the cytotrophoblast cells and weaker staining in the syncytiotrophoblasts. The cytotrophoblasts also displayed conspicuous surface staining with the monoclonal antibodies E11 and G11, which recognize a Ca2+ receptor mechanism regulating hormone release of parathyroid cells. Cytotrophoblasts enriched on Percoll gradients or by linking surface-bound E11 to magnetic beads revealed biphasic elevation of cytoplasmic Ca2+ ([Ca2+]i) upon a stepwise rise of external Ca2+ from 0.5 to 3.0 mm, with a half-maximal effect at 1.75 mm. Individual cytotrophoblasts identified by their E11 reactivity disclosed a temporary increase of [Ca2+]i upon elevation of external Mg2+, while Mn2+ triggered both a [Ca2+]i transient and an influx of itself. These effects were efficiently blocked by the G11 antibody. Depolarization with K+ or addition of the voltage-dependent Ca2+ channel blocker verapamil had only marginal effects on [Ca2+]i. Raised extracellular calcium inhibited release of PTHrp from the cells, and this inhibition was blocked by the G11 antibody. The virtually parathyroid-identical Ca2+ regulation of [Ca2+]i may mediate feedback control of PTHrp release from the cytotrophoblasts and thereby participate in the regulation of placental Ca2+ transport.