Extracellular Ca2+ sensing by the osteoclast

Zaidi, Mone; Alam, A. S. M. Towhidul; Huang, Christopher L.‐H.; Pazianas, Michael; Bax, Christopher M.R.; Bax, Bridget E.; Moonga, Baljit S.; Bevis, Peter J. R.; Shankar, Vijai S.

doi:10.1016/0143-4160(93)90048-b

Cited by 68 publications

(64 citation statements)

References 42 publications

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“…Osedax males are significantly smaller than females, ranging from 0.3 to 1 mm in length, and, depending on the species, hundreds of 'dwarf' males may inhabit the tube of a single female with the only purpose of producing sperm to fertilize her eggs. The males lack symbiotic bacteria and seem to rely on yolk reserves only for sperm production [1,5,6].…”

Section: Introductionmentioning

confidence: 99%

How to get into bones: proton pump and carbonic anhydrase inOsedaxboneworms

2013

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Osedax are gutless siboglinid worms that thrive on vertebrate bones lying on the ocean floor, mainly those of whales. The posterior body of female Osedax penetrates into the bone forming extensions known as 'roots', which host heterotrophic symbiotic bacteria in bacteriocytes beneath the epidermis. The Osedax root epithelium presumably absorbs bone collagen and/or lipids, which are metabolized by the symbiotic bacteria that in turn serve for Osedax's nutrition. Here, we show that Osedax roots express extremely high amounts of vacuolar-H þ -ATPase (VHA), which is located in the apical membrane and in cytoplasmic vesicles of root and ovisac epithelial cells. The enzyme carbonic anhydrase (CA), which catalyses the hydration of CO 2 into H þ and HCO 3 2 , is also expressed in roots and throughoutOsedax body. These results suggest Osedax roots have massive acid-secreting capacity via VHA, fuelled by H þ derived from the CA-catalysed hydration of CO 2 produced by aerobic metabolism. We propose the secreted acid dissolves the bone carbonate matrix to then allow the absorption of bonederived nutrients across the skin. In an exciting example of convergent evolution, this model for acid secretion is remarkably similar to mammalian osteoclast cells. However, while osteoclasts dissolve bone for repairing and remodelling, the Osedax root epithelium secretes acid to dissolve foreign bone to access nutrients.

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Section: Introductionmentioning

confidence: 99%

How to get into bones: proton pump and carbonic anhydrase inOsedaxboneworms

2013

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“…It has recently been discovered that certain cells can monitor changes in the extracellular Ca2+ concentration using a plasma membrane divalent cation-sensing receptor, the Ca2`receptor (CaR) (7,8). Such cells include osteoclasts (9,10), parathyroid chief cells (7,11), thyroid C cells ( 12,13), juxtaglomerular cells ( 14), enterocytes ( 15), and keratinocytes ( 16).…”

Section: Introductionmentioning

confidence: 99%

A ryanodine receptor-like molecule expressed in the osteoclast plasma membrane functions in extracellular Ca2+ sensing.

Zaidi

Shankar²,

Tunwell³

et al. 1995

J. Clin. Invest.

115

108

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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) Ca2" elevations induced by Ni2". In contrast, the responses to Ni2" were strongly potentiated by an antiserum Ab"2 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 AbM 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 an important role in extracellular Ca2" sensing. (J. Clin. Invest. 1995.

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“…Other divalent cations, such as Co2+ and Ni2+, also inhibited the inwardly rectifying K+ current. The inhibition of inwardly rectifying K+ channels was greatly attenuated by the intracellular application of GDPflS but was not affected by PTX, (Bax et al 1992;Zaidi et al 1993). The presence of similar [Ca2+].…”

Section: Discussionmentioning

confidence: 99%

“…As in the case of Ca2+, Co2+ inhibited the inwardly rectifying K+ current in a dose-dependent manner. Figure 3C compares Involvement of the G-protein in the inhibition of the inwardly rectifying K+ current In neuronal cells and heart muscle cells, inwardly rectifying K+ channels are regulated by various agonists and antagonists through G-proteins (Brown & Birnbaumer, 1990 [Ca21]0 is considered to be mediated by the putative Ca2+ receptor or sensor (Bax et al 1992;Zaidi et al 1993 Figure 4C shows the I-Vrelationships of the membrane current when 200 /1M GDP/JS was intracellularly applied through the patch pipette. The intracellular application of GDP/JS greatly attenuated the inhibition of inwardly rectifying K+ channels caused by high [Ca21]..…”

Section: Pertussis Toxin Treatmentmentioning

confidence: 99%

“…It is known that the intracellular Ca2+ concentration ([Ca2+]i) of osteoclasts increases and that cells contract in response to an elevation of [Ca2+]O. These responses may be mediated through a Ca2+ receptor or a sensor on the osteoclast cell membrane (Bax, Shankar, Moonga, Huang & Zaidi, 1992;Zaidi et al 1993). However, little is known about how ionic channels of osteoclasts are regulated by [Ca2+]O.…”

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