The exchange of bone CO2 in vivo

Bone 14CO2 specific activities have been measured in 10 male rats perfused for 30, 60 or 120 minutes with [14C]bicarbonate. A steady blood 14CO2 specific activity is observed from the 30th minute, whereas bone 14CO2 specific activity increased linearly with time. About 7-10% of the total activity infused may be recovered in the skeleton at any given time. Bone samples heated to constant weight lost 15% of their total CO2 content and more than 50% of the 14CO2 activity. This indicates that 14CO2 present in bone is almost exclusively located in a bicarbonate pool which may be considered as the rapidly exchangeable bone CO2 fraction. The rate of exchange between bone and blood CO2 is estimated at a maximum of 15% of the total CO2 production. It is postulated that blood flow to the skeleton is the limiting factor for bone CO2 exchange. These results lead to the conclusion that the large bone CO2 store cannot play a significant role in the buffering of extracellular fluids in acute acid-base abnormalities.