TY - JOUR
T1 - Bone as an ion exchange organ
T2 - Evidence for instantaneous cell-dependent calcium efflux from bone not due to resorption
AU - Marenzana, M.
AU - Shipley, A. M.
AU - Squitiero, P.
AU - Kunkel, J. G.
AU - Rubinacci, A.
PY - 2005/10
Y1 - 2005/10
N2 - The current study tests the hypothesis that basal level and minute-by-minute correction of plasma Ca2+ by outward and inward Ca2+ fluxes from and into an exchangeable ionic pool in bone is controlled by an active partition system without contributions from the bone remodeling system. Direct real-time measurements of Ca2+ fluxes were made using the scanning ion-selective electrode technique (SIET) on living bones maintained ex vivo in physiological conditions. SIET three-dimensional measurements of the local Ca2+ concentration gradient (10 μm spatial resolution) were performed on metatarsal bones of weanling mice after drilling a 100-μm hole through the cortex to expose the internal bone extracellular fluid (BECF) to the bathing solution, whose composition mimicked the extracellular fluid (ECF). Influxes of Ca2+ towards the center of the cortical hole (15.1 ± 4.2 pmol cm-2 s-1) were found in the ECF and were reversed to effluxes (7.4 ± 2.9 pmol cm -2 s-1) when calcium was depleted from the ECF, mimicking a plasma demand. The reversal from influx to efflux and vice versa was immediate and fluxes in both directions were steady throughout the experimental time (≥2 h, n = 14). Only the efflux was nullified within 10 min by the addition of 10 mM/L Na-Cyanide (n = 7), demonstrating its cell dependence. The timeframes of the exchanges and the stability of the Ca2+ fluxes over time suggest the existence of an exchangeable calcium pool in bone. The calcium efflux dependency on viable cells suggests that an active partition system might play a central role in the short-term error correction of plasma calcium without the contribution of bone remodeling.
AB - The current study tests the hypothesis that basal level and minute-by-minute correction of plasma Ca2+ by outward and inward Ca2+ fluxes from and into an exchangeable ionic pool in bone is controlled by an active partition system without contributions from the bone remodeling system. Direct real-time measurements of Ca2+ fluxes were made using the scanning ion-selective electrode technique (SIET) on living bones maintained ex vivo in physiological conditions. SIET three-dimensional measurements of the local Ca2+ concentration gradient (10 μm spatial resolution) were performed on metatarsal bones of weanling mice after drilling a 100-μm hole through the cortex to expose the internal bone extracellular fluid (BECF) to the bathing solution, whose composition mimicked the extracellular fluid (ECF). Influxes of Ca2+ towards the center of the cortical hole (15.1 ± 4.2 pmol cm-2 s-1) were found in the ECF and were reversed to effluxes (7.4 ± 2.9 pmol cm -2 s-1) when calcium was depleted from the ECF, mimicking a plasma demand. The reversal from influx to efflux and vice versa was immediate and fluxes in both directions were steady throughout the experimental time (≥2 h, n = 14). Only the efflux was nullified within 10 min by the addition of 10 mM/L Na-Cyanide (n = 7), demonstrating its cell dependence. The timeframes of the exchanges and the stability of the Ca2+ fluxes over time suggest the existence of an exchangeable calcium pool in bone. The calcium efflux dependency on viable cells suggests that an active partition system might play a central role in the short-term error correction of plasma calcium without the contribution of bone remodeling.
KW - Calcium flux
KW - Ion-selective vibrating probe
KW - Osteocyte-bone lining cells synctium
KW - Plasma calcium homeostasis
KW - Short-term error correction of plasma calcium
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U2 - 10.1016/j.bone.2005.04.036
DO - 10.1016/j.bone.2005.04.036
M3 - Article
C2 - 16046204
AN - SCOPUS:24944500478
VL - 37
SP - 545
EP - 554
JO - Bone
JF - Bone
SN - 8756-3282
IS - 4
ER -