Physicochemical effects of acidosis on bone calcium flux and surface ion composition

Abstract

Net calcium flux (JCa) from bone in vitro is pH dependent. When pH falls below 7.40, through a reduction in [HCO3-], there is both physicochemical and cell-mediated JCa. To characterize the physicochemical effect of acidosis on bone we inhibited the bone-resorbing cells (osteoclasts) with the specific inhibitor calcitonin and studied the effect of acidosis on JCa and bone ion composition using an analytic high-resolution scanning ion microprobe. Neonatal mouse calvariae were cultured for 48 h in physiologically neutral pH medium (Ntl, pH = 7.41, [HCO3-] = 25 nM) or in medium that modeled metabolic acidosis (Met, pH = 7.10, [HCO3-] = 12), each with or without calcitonin (CT, 3 x 10(-9) M). There was net calcium efflux in Ntl (JCa = 631 +/- 36 nmol per bone per 48 h), which increased in Met (1019 +/- 53, p < 0.01); CT inhibited JCa in Ntl (-54 +/- 11, p < 0.01 versus Ntl), which increased in Met (197 +/- 15, p < 0.01 versus Ntl + CT). In the presence of CT the increase in JCa in Met versus Ntl represents physiochemical bone dissolution. The Ntl bone surface (approximately 2 nm in depth) was rich in Na compared to Ca (Na/Ca = 11.9, count/s of detected secondary ions), which fell in Met (Na/Ca = 6.0, p < 0.05); CT caused a further reduction of Na/Ca (3.1, p < 0.01 versus Ntl and versus Met), which was not altered in Met (2.6, p < 0.05 versus Ntl + CT).(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of dietary cation-anionic difference on hematobio chemical profile, mineral metabolism, post-partum reproductive and productive performance of Hariana cows

“…Increased plasma Ca level in + 11 meq/100 g of DM fed diet might be due to higher dietary Ca level. High plasma Ca level may also be attributed to increased Ca absorption from the alimentary tract (Lomba et al, 1978) and Ca mobilization from bones (Bushinsky et al, 1993) due to mild metabolic acidosis, induced by feeding low DCAD diet. Feeding a low DCAD increased the flow of Ca through the readily exchangeable Ca pool (Takagi and Block, 1988) and enhanced the concentration of ionized Ca in the blood (Oetzel et al, 1988).…”

“…In the periparturient period from advanced pregnancy to early lactation, the clearance of Ca to the placenta ceases, but the lactational Ca demand increases rapidly (Ramberg et al, 1984). The reduction of body fluids pH by addition of low dietary cation-anion difference (DCAD) diet can help in Ca mobilization (Takagi and Block, 1988;Bushinsky et al, 1993;Schonewille et al, 1994). The direct implementation of the findings obtained from the studies executed on exotic dairy cows to the indigenous breed that differs in physiological aspects and thrive on dry fodder dominated feeding system would not be a scientific approach.…”

Acid–Base Balance and Bone Health

“…The in vitro evidence for proton buffering by bone is derived from studies of acidosis-induced proton influx into bone [22][23][24] and microprobe evidence for a depletion of bone sodium and potassium during acidosis [25,26,30,31,89]. When calvariae are cultured in medium acidified by a decrease in the concentration of bicarbonate (metabolic acidosis), there is a net influx of protons into the bone, decreasing the medium proton concentration and indicating that the additional hydrogen ions are being buffered by bone [22][23][24] (Fig.…”

“…The in vivo evidence that bone acutely buffers protons, and in the process releases calcium, derives principally from the loss of bone sodium and/or potassium [25][26][27][28][29][30][31], carbonate [23,29,32,33] and the increase in serum calcium [34] observed during acidosis. Bone sodium (or potassium) loss implies proton for sodium (or potassium) exchange and carbonate loss suggests consumption of this buffer by the administered protons.…”

“…Calvariae cultured in acidic medium exhibit proton-dependent net calcium efflux during both acute (3 h) and more chronic (>24-99 h) incubations [2,3,9,23,24,26,30,32,[69][70][71]. During acute incubations there was net calcium efflux from the calvariae when medium pH was decreased to less than the physiologic normal of 7.40 by decreasing the [HCO 3 − ], no net flux at a neutral physiologic pH and an influx of calcium into bone when pH was greater than 7.40 [24] (Fig.…”