METABOLISM AND ENERGETICS IN SQUID (ILLEX-ILLECEBROSUS, LOLIGO-PEALEI) DURING MUSCULAR FATIGUE AND RECOVERY

The concentrations of intermediate and end products of anaerobic energ y metabolism and of free amino acids were determined in mantle muscula ture and blood sampled from cannulated, unrestrained squid (Loligo pea lei, Illex illecebrosus) under control conditions, after fatigue from increasing levels of exercise, and during postexercise recovery. Phosp hagen depletion, accumulation of octopine (more so in Illex than in Lo ligo), and accumulation of succinate indicate that anaerobic metabolis m contributes to energy production before fatigue. Proline was a subst rate of metabolism in Loligo, as indicated by its depletion in the man tle. In both species, there was no evidence of catabolism of ATP beyon d AMP. A comparison of the changes in the free and total levels of ade nylates and the phosphagen indicates an earlier detrimental effect of fatigue on the energy status in Loligo. The acidosis provoked by octop ine formation in Illex was demonstrated to promote the use of the phos phagen and to protect the free energy change of ATP such that the anae robic scope of metabolism during swimming is extended and expressed mo re in Illex than in Loligo. In both species, there was no decrease in the sum of phospho-L-arginine, octopine, and L-arginine, and thus no r elease of octopine from the mantle, thereby supporting our earlier cla im that octopine and associated protons are recycled in the mantle tis sue. Overall, the metabolic strategy of Loligo is much less disturbing for the acid-base status. This strategy and the alternative strategy of Illex to keep acidifying protons in the tissue may be important for the protection of hemocyanin function in the two species.