Adenine nucleotide levels and adenosine metabolism in cultured calvarial bone

Adenine nucleotide levels were measured in extracts of murine calvaria after different periods of culture with or without parathyroid hormone (PTH; 10(-8) M) or PGE2 (10(-7) M). In control calvaria the energy charge, (ATP + 1/2 ADP)/(ATP + ADP + AMP), remained at close to 0.7 over a 24 hour culture period. However, bones cultured with PTH or PGE2 showed a transient fall in the energy charge down to 0.5. This was not associated with a fall in total adenine nucleotides. The rate of adenosine metabolism in cultured bone in vitro was studied by determining the contents of adenosine, inosine, 2-deoxyadenosine, 2-deoxyinosine and hypoxanthine in the culture medium. There was a continuous increase in adenosine, inosine and hypoxanthine as well as a disappearance of medium 2-deoxyadenosine that was accounted for by appearance of 2-deoxyinosine. The deaminating activity could only partly be accounted for by activity in the medium and thus probably mainly resides in the bone cells. PTH (10(-8) M) did not alter the rate of disappearance of 2-deoxyadenosine or adenosine deaminase activity determined in bone extracts. The results demonstrate that two substances that increase calcium mobilization from bone alter ATP utilization and/or synthesis without significantly influencing adenosine production or metabolism.