The export of cellular glucose depends on the endoplasmic reticulum bound enzyme glucose-6-phosphatase (G-6-Pase), which catalyzes the hydrolysis of glucose-6-phosphate to glucose-6, the final step required for the release of new glucose into the blood or hemolymph. The current study examined the effect of chloride on G-6-Pase activity in two marine crustaceans: the ion-regulating crab Menippe mercenaria, and the ion-conforming crab Libinia dubia. Elevated chloride (from 0 to 250 mmol L−1 Cl−) stimulated hepatopancreas G-6-Pase activity in both crabs (2 times in M. mercenaria and up to 1.6 times in L. dubia). Elevated chloride also increased glucose export from isolated M. mercenaria hepatopancreas. These results are in stark contrast to G-6-Pase chloride inhibition previously reported in vertebrate liver. The sensitivity of G-6-Pase to changes in environmental chloride was determined in crabs acclimated to low (20‰) and high (45‰) salinity. M. mercenaria acclimated to high salinity became less sensitive to changes in chloride, G-6-Pase activity decreased by about half. Our results suggest that chloride may be an important regulator of gluconeogenesis in marine crustaceans and may help ensure adequate glucose release during times of high metabolic demand such as exposure to variable salinity.
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Vol. 26 • No. 4