An ATP pool with rapid turnover within the cell membrane

Seven-day-old cultures of rat leg muscle cells were double labelled by addition of [¹⁴C] adenine in the culture medium (2 hrs 15 mins) and followed by addition of [³²P] phosphate (15 min). The specific activity (S.A.) of the isolated cyclic [¹⁴C] adenine 3′ – 5′ monophosphate (cAMP) was similar to that of the bulk ATP. The S.A. of [³²P] from cAMP was, however, higher than that of bulk ATP. The S.A. of [³²P] from cAMP could be further modified by prevention of normal muscle cell fusion. It is probable that the cAMP with high [³²P] S.A. was synthesized from a cell membrane pool of ATP with rapid turnover.