Calcium fluxes at the bone/plasma interface: Acute effects of parathyroid hormone (PTH) and targeted deletion of PTH/PTH-related peptide (PTHrP) receptor in the osteocytes

“Ca 2+ homeostasis through the reversible enlargement of the osteocyte lacunae and demineralization of the surrounding matrix under high Ca 2+ demand (38, 39, 65), our study raises the hypothesis that minute-to-minute maintenance of Ca 2+ equilibrium at the bone surfaces does not require any rapid action of PTH on the…”

“The hormone (100 nM human PTH(1-34) was added to the metatarsal medium and the Ca 2+ fluxes at the bone site were recorder for 5 consecutive minutes.”

“Indeed, calcemic responses to PTH and M-PTH(1-28) - a long acting PTH analog - were similar in both DMP1-Cre:PPRfl/fl and control mice.”

“5 nanocrystals as well as to the organic phase (24, 25) that are instantly exchangeable with the plasma (26).”

“the surface of the osteocytic lacunae (71, 72).”

“The hormone (100 nM human PTH(1-34) was added to the metatarsal medium and the Ca 2+ fluxes at the bone site were recorder for 5 consecutive minutes.”

“The hormone (100 nM human PTH(1-34) was added to the metatarsal medium and the Ca 2+ fluxes at the bone site were recorder for 5 consecutive minutes.”

“Indeed, calcemic responses to PTH and M-PTH(1-28) - a long acting PTH analog - were similar in both DMP1-Cre:PPRfl/fl and control mice.”

“transport via the permeability of the paracellular pathway to Ca 2+ (75).”

“Indeed, calcemic responses to PTH and M-PTH(1-28) - a long acting PTH analog - were similar in both DMP1-Cre:PPRfl/fl and control mice.”

“well as osteoclast resorption, require the reversible activation, in osteocytes as well as in osteoclasts, of genes typically associated with bone resorption (70), and are induced under the physiological condition of a long-term high Ca 2+ demand, such as during lactation (36, 65) and/or a low Ca 2+ diet (52).”

“In addition, it has been proposed that bone lining cells (BLCs), covering the quiescent surfaces of bone, might constitute a “bone membrane” (10, 41-48), acting as a partition system between BECF and ECF (48-51).”

“Ca 2+ homeostasis (30-32), but its hormonal regulation remains unsettled despite its importance in the overall plasma Ca 2+ homeostasis.”

“well as osteoclast resorption, require the reversible activation, in osteocytes as well as in osteoclasts, of genes typically associated with bone resorption (70), and are induced under the physiological condition of a long-term high Ca 2+ demand, such as during lactation (36, 65) and/or a low Ca 2+ diet (52).”

“components can be supplied by bone lining cells that might change the permeability of the interface between the lacunar-canalicular porosity and the collagen-hydroxyapatite porosity (22, 56) and/or control the access to organic and inorganic Ca 2+ binding sites (15, 41).”

“In addition, it has been proposed that bone lining cells (BLCs), covering the quiescent surfaces of bone, might constitute a “bone membrane” (10, 41-48), acting as a partition system between BECF and ECF (48-51).”

“Deviation of plasma Ca 2+ from set-point modulates osteoclastogenesis (54) and has profound effects on bone cell fate and activities, by means of the Ca 2+ sensing receptor (CaSR) and independently of systemic calciotropic peptides (55).”

“mineralized matrix without the need to activate an osteoclast-like function of matrix lysis (35) since they are ideally placed to establish a direct and extensive contact to a mineralized matrix (36, 37); can regulate virtually every phase of the mineralization process (36); can dissolve minerals through canaliculi by…”

“Key reviews reporting representative experiments have been recently published (34, 59) and the SIET basic principles have been outlined (60).”

“The demonstration that the CaSR is a direct, PTH-independent determinant of blood [Ca 2+ ] (76) suggests that the CaSR - beyond being a component of the Ca 2+ /PTH axis and a regulator of tubular Ca 2+ reabsorption - might be essential in Ca 2+ homeostasis for its potential role at the bone/plasma interface where it m…”

“Indeed, calcemic responses to PTH and M-PTH(1-28) - a long acting PTH analog - were similar in both DMP1-Cre:PPRfl/fl and control mice.”

“Via the unique opportunity offered by SIET to obtain direct real-time measurements of Ca 2+ fluxes and concentration gradients at the bone/plasma Ca 2+ interface (34, 57, 58, 60), and by applying the previously validated method of ex vivo metatarsal bones in physiological conditions (33), we have now been able to prov…”

“In addition, it has been proposed that bone lining cells (BLCs), covering the quiescent surfaces of bone, might constitute a “bone membrane” (10, 41-48), acting as a partition system between BECF and ECF (48-51).”

“Ca 2+ homeostasis through the reversible enlargement of the osteocyte lacunae and demineralization of the surrounding matrix under high Ca 2+ demand (38, 39, 65), our study raises the hypothesis that minute-to-minute maintenance of Ca 2+ equilibrium at the bone surfaces does not require any rapid action of PTH on the…”

“The hormone (100 nM human PTH(1-34) was added to the metatarsal medium and the Ca 2+ fluxes at the bone site were recorder for 5 consecutive minutes.”

“5 nanocrystals as well as to the organic phase (24, 25) that are instantly exchangeable with the plasma (26).”

“well as osteoclast resorption, require the reversible activation, in osteocytes as well as in osteoclasts, of genes typically associated with bone resorption (70), and are induced under the physiological condition of a long-term high Ca 2+ demand, such as during lactation (36, 65) and/or a low Ca 2+ diet (52).”

“The hormone (100 nM human PTH(1-34) was added to the metatarsal medium and the Ca 2+ fluxes at the bone site were recorder for 5 consecutive minutes.”

“Ca 2+ homeostasis through the reversible enlargement of the osteocyte lacunae and demineralization of the surrounding matrix under high Ca 2+ demand (38, 39, 65), our study raises the hypothesis that minute-to-minute maintenance of Ca 2+ equilibrium at the bone surfaces does not require any rapid action of PTH on the…”

“PTH induces indeed a calcemic response that is significant at 1 to 2 h post injection (62).”

“Experiments and models addressed to assess the contribution of PTH [see (13, 15, 18) for reviews] have suggested that the level of blood/bone equilibrium might vary with the level of PTH, but the direct experimental evidence for the PTH effect at the bone surface in eliciting a fast homeostatic response is lacking.”

“Ca 2+ -specific ISM for bone measurement at 37°C have been previously described (33).”

“The hormone (100 nM human PTH(1-34) was added to the metatarsal medium and the Ca 2+ fluxes at the bone site were recorder for 5 consecutive minutes.”

“SIET could be applied to solve this question since it can provide a contemporary assessment of H + and Ca 2+ fluxes at the bone/plasma interface in real-time (60, 61).”

“In addition, it has been proposed that bone lining cells (BLCs), covering the quiescent surfaces of bone, might constitute a “bone membrane” (10, 41-48), acting as a partition system between BECF and ECF (48-51).”

“assure optimal probe sensitivity and stability, and to detect potential transient influx of Ca 2+ into bone after PTH addition, as suggested by some early study with 45 Ca 2+ (64).”

“The existence of a “functional” epithelial-like bone membrane operating in Ca 2+ homeostasis was foreseen by pioneering experiments based upon radioactive Ca 2+ distribution in bone (78).”

“Recently, this view is sustained by the observation that claudins (tight junction membrane proteins) have been reported to regulate and restrict paracellular ion transport at the bone/plasma interface according to the metabolic demand (79, 80).”

“Indeed, calcemic responses to PTH and M-PTH(1-28) - a long acting PTH analog - were similar in both DMP1-Cre:PPRfl/fl and control mice.”

“Via the unique opportunity offered by SIET to obtain direct real-time measurements of Ca 2+ fluxes and concentration gradients at the bone/plasma Ca 2+ interface (34, 57, 58, 60), and by applying the previously validated method of ex vivo metatarsal bones in physiological conditions (33), we have now been able to prov…”

“In addition, it has been proposed that bone lining cells (BLCs), covering the quiescent surfaces of bone, might constitute a “bone membrane” (10, 41-48), acting as a partition system between BECF and ECF (48-51).”

“The hormone (100 nM human PTH(1-34) was added to the metatarsal medium and the Ca 2+ fluxes at the bone site were recorder for 5 consecutive minutes.”

“The hormone (100 nM human PTH(1-34) was added to the metatarsal medium and the Ca 2+ fluxes at the bone site were recorder for 5 consecutive minutes.”

“Indeed, calcemic responses to PTH and M-PTH(1-28) - a long acting PTH analog - were similar in both DMP1-Cre:PPRfl/fl and control mice.”

“Indeed, calcemic responses to PTH and M-PTH(1-28) - a long acting PTH analog - were similar in both DMP1-Cre:PPRfl/fl and control mice.”

“The hormone (100 nM human PTH(1-34) was added to the metatarsal medium and the Ca 2+ fluxes at the bone site were recorder for 5 consecutive minutes.”

“Isolation of metatarsal bones was done as previously described (33, 42-44).”

“Ca 2+ -EGTA complex and the rapid increase in plasma [Ca 2+ ] after the brief induction of hypocalcemia in PTH depleted animals (74), the overall conclusion of these studies, as stated by the authors, was that PTH is not a prerequisite for the rapid correction of ECF-[Ca 2+ ], although they later observed that the rec…”

“In addition, it has been proposed that bone lining cells (BLCs), covering the quiescent surfaces of bone, might constitute a “bone membrane” (10, 41-48), acting as a partition system between BECF and ECF (48-51).”

“Indeed, calcemic responses to PTH and M-PTH(1-28) - a long acting PTH analog - were similar in both DMP1-Cre:PPRfl/fl and control mice.”

“The hormone (100 nM human PTH(1-34) was added to the metatarsal medium and the Ca 2+ fluxes at the bone site were recorder for 5 consecutive minutes.”

“The hormone (100 nM human PTH(1-34) was added to the metatarsal medium and the Ca 2+ fluxes at the bone site were recorder for 5 consecutive minutes.”

“out of bone, and maintaining Ca 2+ level in the bone fluid lower than that in the general extracellular fluid (67).”

“In addition, it has been proposed that bone lining cells (BLCs), covering the quiescent surfaces of bone, might constitute a “bone membrane” (10, 41-48), acting as a partition system between BECF and ECF (48-51).”

“Ca 2+ homeostasis (30-32), but its hormonal regulation remains unsettled despite its importance in the overall plasma Ca 2+ homeostasis.”

“Ca 2+ homeostasis (30-32), but its hormonal regulation remains unsettled despite its importance in the overall plasma Ca 2+ homeostasis.”

“exchange at the bone/plasma interface is higher than the average daily flux due to bone turnover regardless of the degree of mineralization or turnover state (19).”

“Deviation of plasma Ca 2+ from set-point modulates osteoclastogenesis (54) and has profound effects on bone cell fate and activities, by means of the Ca 2+ sensing receptor (CaSR) and independently of systemic calciotropic peptides (55).”

“Indeed, calcemic responses to PTH and M-PTH(1-28) - a long acting PTH analog - were similar in both DMP1-Cre:PPRfl/fl and control mice.”

“Experiments and models addressed to assess the contribution of PTH [see (13, 15, 18) for reviews] have suggested that the level of blood/bone equilibrium might vary with the level of PTH, but the direct experimental evidence for the PTH effect at the bone surface in eliciting a fast homeostatic response is lacking.”

“5 nanocrystals as well as to the organic phase (24, 25) that are instantly exchangeable with the plasma (26).”

“Via the unique opportunity offered by SIET to obtain direct real-time measurements of Ca 2+ fluxes and concentration gradients at the bone/plasma Ca 2+ interface (34, 57, 58, 60), and by applying the previously validated method of ex vivo metatarsal bones in physiological conditions (33), we have now been able to prov…”

“In all these studies, the rapid recovery of plasma [Ca 2+ ] was examined after EGTA-related induction of hypocalcemia in parathyroidectomized rats, and rats treated with PTH (73).”

“As previously described (44), the unique design of the experimental chamber and the use of mineral oil was aimed at reducing to a reasonable minimum the exchange of CO2 between the incubation medium and the ambient atmosphere.”

“Recently, this view is sustained by the observation that claudins (tight junction membrane proteins) have been reported to regulate and restrict paracellular ion transport at the bone/plasma interface according to the metabolic demand (79, 80).”

“mineralized matrix without the need to activate an osteoclast-like function of matrix lysis (35) since they are ideally placed to establish a direct and extensive contact to a mineralized matrix (36, 37); can regulate virtually every phase of the mineralization process (36); can dissolve minerals through canaliculi by…”

“Isolation of metatarsal bones was done as previously described (33, 42-44).”

“Our study challenges earlier reports that have hypothesized that bone-mediated minute-to-minute regulation of plasma Ca 2+ by PTH are due to Ca 2+ transport from bone without osteolysis (66).”

“[Ca 2+ ] in thyro-parathyroidectomized rats was significantly impaired in rats treated with the CaSR activators, R-568 and gentamycin (77).”

“Perilacunar osteocytes remodeling (68), and synergic osteoclastic activity through the RANK/RANKL pathway (69), which are expected to be reduced due to the ablation of PTH/PTHrp receptor, might require a time longer that the fast and reversible fluxes of Ca 2+”

“Thus, our data indicate that scales show a similar short-term Ca2+-related homeostatic activity to that previously reported for mammalian bone (Marenzana et al. 2005; Dedic et al. 2018).”

“Furthermore, the ability to recapitulate a developmental event from an intact embryo in an embryonic tissue explant illustrates the robust nature of X. laevis embryos as a developmental model (DeSimone et al., 2005).”

“These include the assessment of urinary fluoride as a diagnostic marker for fluorosis [39], the monitoring of serum fluoride after spinal fusion [38], and calcium fluxes at the bone–plasma interface studied with SIET in ex vivo models [21].”