In perfused rat hearts ischaemia promotes the reversible conversion of appreciable quantities of soluble adenine nucleotides to a stable trichloroacetic acid-precipitable form.

Radioactivity from [14C] adenosine was linearly incorporated into tissue nucleotides in perfused rat hearts. All the TCA-extractable 14C was confined to the purine nucleoside phosphates for up to 1 h of perfusion. Radioactivity was also incorporated linearly into the TCA-insoluble fraction, which by 40 min accounted for 24% of the tissue 14 C. Estimates based on precursor specific radioactivity suggest that at least 0.6 micro mol/g of the mononucleotide is in this stable insoluble form. Following 2 min total ischaemia, the tissue nucleotide content and soluble radioactivity decreased while the insoluble radioactivity showed a corresponding increase to account now for 35% of the tissue radiolabel. This redistribution was rapidly reversed by post-ischaemic reperfusion. A possible function for the rapid reversible sequestration of adenine nucleotides in ischaemia is proposed.