Physicochemical effects of acidosis on bone calcium flux and surface ion composition.
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)
Bushinsky
D A
DA
Nephrology Unit, University of Rochester School of Medicine and Dentistry, New York.
Wolbach
W
W
Sessler
N E
NE
Mogilevsky
R
R
Levi-Setti
R
R
D000818:Animals; D000831:Animals, Newborn; D001842:Bone and Bones / Q000166:cytology / Q000378:metabolism*; D002116:Calcitonin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D006863:Hydrogen-Ion Concentration; D051379:Mice; D010010:Osteoclasts / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism
D002116:Calcitonin; D012964:Sodium; D011188:Potassium; D002118:Calcium