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Ryanodine receptors (RyRs) reside in microsomal membranes where they gate Ca2+ release in response to changes in the cytosolic Ca2+ concentration. In the osteoclast, a divalent cation sensor, the Ca2+ receptor (CaR), located within the cell's plasma membrane, monitors changes in the extracellular Ca2+ concentration. Here we show that a RyR-like molecule is a functional component of this receptor. We have demonstrated that [3H] ryanodine specifically binds to freshly isolated rat osteoclasts. The binding was displaced by ryanodine itself, the CaR agonist Ni2+ and the RyR antagonist ruthenium red. The latter also inhibited cytosolic Ca2+ elevations induced by Ni2+. In contrast, the responses to Ni2+ were strongly potentiated by an antiserum Ab129 raised to an epitope located within the channel-forming domain of the type II RyR. The antiserum also stained the surface of intact, unfixed, trypan blue-negative osteoclasts. Serial confocal sections and immunogold scanning electron microscopy confirmed a plasma membrane localization of this staining. Antiserum Ab34 directed to a putatively intracellular RyR epitope expectedly did not stain live osteoclasts nor did it potentiate CaR activation. It did, however, stain fixed, permeabilized cells in a distinctive cytoplasmic pattern. We conclude that an RyR-like molecule resides within the osteoclast plasma membrane and plays in important role in extracellular Ca2+ sensing.

Original publication

DOI

10.1172/jci118197

Type

Journal article

Journal

The Journal of clinical investigation

Publication Date

09/1995

Volume

96

Pages

1582 - 1590

Addresses

St. George's Hospital Medical School, University of London, United Kingdom.

Keywords

Cells, Cultured, Cell Membrane, Cytosol, Osteoclasts, Animals, Animals, Newborn, Mammals, Rats, Rats, Wistar, Calcium, Tritium, Ryanodine, Calcium Channels, Ryanodine Receptor Calcium Release Channel, Muscle Proteins, Microscopy, Confocal, Fluorescent Antibody Technique, Autoradiography, Gene Expression