Energy Metabolism during Contractile Activity and Environmental Hypoxia in the Phasic Adductor Muscle of the Bay Scallop Argopecten irradians concentricus

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Abstract
The bay scallop Argopecten irradians concentricus responds to the approach of a predatory gastropod with an escape swimming behavior which is produced by rapid contractions of the phasic adductor muscle. In addition, this species can survive under hypoxic conditions (PO₂ < 20 mm Hg) for at least 10 h. Studies were undertaken to assess the mode of energy production in the adductor muscle during contractile activity and subsequent recovery and during environmental hypoxia. During the organism's initial swimming response, the bulk of ATP utilized in adductor muscle contraction was derived from arginine phosphate. Glycolysis provided the bulk of energy during additional swimming sequences, with tissue octopine levels rising from 0.05 to 8.22 μmol · g wet . During the organism's recovery after swimming to exhaustion, arginine phosphate levels were rapidly restored, while octopine levels declined. During 4 h of hypoxia there was no accumulation of octopine in the phasic adductor muscle of A. irradians concentricus. There was a decline in arginine phosphate; succinate was accumulated as an end product. Following 4 h of hypoxia, some scallops were induced to swim and showed 15-22 contractions of the adductor muscle. This posthypoxic contractile activity resulted in significant production of octopine (0.49-3.77 μmol · g wet ) as well as accumulation of alanine, succinate, and alanopine/strombine. Octopine production is clearly restricted to periods of contractile activity in the phasic adductor muscle of A. irradians concentricus and does not occur during environmental hypoxia or recovery after swimming.

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