Changes of nucleotide contents and of energy charge induced by contraction, catch and relaxation in smooth molluscan muscle fibres. An analysis using reversed-phase ion-pair high-performance liquid chromatography.

1. The content of 14 different nucleotides, including cAMP, in isolated muscle fibres of the anterior byssus retractor muscle of Mytilus edulis was analysed. The nucleotide levels were determined after the muscle fibres performed phasic, tonic, or tetanic contractions and after serotonin-induced relaxation of tonic contraction. 2. Isolated resting muscle fibres revealed a lower energy charge than freshly-dissected ones. 3. During active force development adenosine energy charge decreased to stay at the same low level during catch, tetanus and serotonin-induced relaxation of catch respectively. 4. The energy charges of the guanosine, uridine and cytidine systems did not show changes parallel to the adenosine system. 5. The levels of cyclic AMP were only changed under the influence of serotonin.