A ryanodine receptor-like molecule expressed in the osteoclast plasma membrane functions in extracellular Ca2+ sensing.
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.
Zaidi
M
M
St. George's Hospital Medical School, University of London, United Kingdom.
Shankar
V S
VS
Tunwell
R
R
Adebanjo
O A
OA
Mackrill
J
J
Pazianas
M
M
O'Connell
D
D
Simon
B J
BJ
Rifkin
B R
BR
Venkitaraman
A R
AR
D000818:Animals; D000831:Animals, Newborn; D001345:Autoradiography; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000032:analysis / Q000096:biosynthesis*; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D015870:Gene Expression; D008322:Mammals; D018613:Microscopy, Confocal; D009124:Muscle Proteins / Q000032:analysis / Q000096:biosynthesis*; D010010:Osteoclasts / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D012433:Ryanodine / Q000378:metabolism*; D019837:Ryanodine Receptor Calcium Release Channel; D014316:Tritium
D015220:Calcium Channels; D009124:Muscle Proteins; D019837:Ryanodine Receptor Calcium Release Channel; D014316:Tritium; D012433:Ryanodine; D002118:Calcium