Buffering Capacities of the Tissues of Marine Molluscs

Abstract

Buffering capacities (β) (measured in slykes = micromoles of base required to titrate the pH of 1 g wet weight of tissue by one pH unit between pH 6 and pH 7) due to nonbicarbonate buffers were measured for the tissues of three marine molluscs, the oyster, Crassostrea virginica, the cherrystone clam, Mercenaria mercenaria, and the channeled whelk, Busycotypus canaliculatum. In general β was higher in muscle tissues (adductors, foot, heart, radular retractor) than in the gill and mantle, but hepatopancreas of the whelk had a β two- to threefold higher than that of any other whelk tissue. Selected tissues (gill of oyster, catch adductor of clam, heart and hepatopancreas of whelk) showed a significant increase in buffering capacity when tissues were isolated from animals held under anoxic conditions compared with control aerobic animals; however, no consistent effect of environmental anoxia was found, nor was buffering capacity related to the tissue levels of succinate accumulated during anaerobiosis. Tissues of oysters and clams showed a positive correlation between β and the activities of terminal glycolytic dehydrogenases, and white muscle-type tissues (adductors, foot) of all three species showed a positive correlation between β and total dehydrogenase activities (lactate, octopine, and alanopine/strombine dehydrogenases). Buffering capacity appears to be related to the tissue need for "burst" glycolytic energy production (functional anoxia) rather than to the capacity for long-term anaerobiosis (environmental anoxia).