Alteration in surface ion composition of cultured bone during metabolic, but not respiratory, acidosis.

Acidosis produced by a fall in [HCO3-] (metabolic acidosis, Met) produces greater Ca efflux from cultured bone than that produced by a rise in PCO2 (respiratory acidosis, Resp). To compare the effects of Met and Resp on bone surface ion composition we measured the surface abundance of 40Ca, 23Na, and 39K in cultured bone with a scanning ion microprobe utilizing secondary-ion mass spectrometry. Neonatal mouse calvariae were incubated for 24 h in medium simulating either Met (pH = 7.193 +/- 0.034, [HCO3-] = 15.1 +/- 1.4 meq/l), Resp (pH = 7.153 +/- 0.014, PCO2 = 85.4 +/- 1.2 mmHg) or normal physiological (Ctl; pH = 7.484 +/- 0.009, [HCO3-] = 29.7 +/- 0.7, PCO2 = 39.6 +/- 0.3) conditions. The surface of Ctl at 2-nm depth is rich in Na and K relative to Ca (Na/Ca = 25.6, K/Ca = 12.0, ratios of counts/s of secondary ions). Compared with Ctl, Met produced a sharp fall in both Na/Ca (6.5, P less than 0.01) and K/Ca (4.6, P less than 0.01), whereas Resp did not alter Na/Ca (23.8) or K/Ca (15.0). Ca efflux was greater in Met (873 +/- 54 nmol.bone-1.24 h-1) than in Resp (546 +/- 71 nmol.bone-1.24 h-1, P less than 0.01), which was greater than that in Ctl (315 +/- 49 nmol.bone-1.24 h-1, P less than 0.01 vs. Met and vs. Resp).(ABSTRACT TRUNCATED AT 250 WORDS)