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Na + -K + -ATPase and Na + /Ca 2+ exchange activities in gills of hyperregulating Carcinus maenas

1999; American Physiological Society; Volume: 276; Issue: 2 Linguagem: Inglês

10.1152/ajpregu.1999.276.2.r490

1522-1490

Čedomil Lucu, Gert Flik,

Physiological and biochemical adaptations

Na + -K + -ATPase and Na + /Ca 2+ exchange activities were studied in gills of Carcinus maenas in seawater (SW) and after transfer to dilute seawater (DSW). Carcinushyperregulates its hemolymph osmolarity through active uptake of Na + , Cl − , and Ca 2+ . In DSW total Na + -K + -ATPase activity in posterior gills quadrupled; Na + /Ca 2+ exchange specific activity was unaffected, and total activity increased 1.67-fold. Short-circuit current ( I sc ) in voltage-clamped posterior gill hemilamellae was −181 μA/cm 2 in SW and −290 μA/cm 2 in DSW and up to 90% ouabain sensitive; conductivity was similar in SW or DSW (42 and 46 mS/cm 2 , respectively) and representative of a leaky epithelium. The new steady state of hemolymph osmolarity 24 h after DSW transfer was preceded, already 3 h after transfer, by increased Na + -K + -ATPase but not Na + /Ca 2+ exchange activity. Western blot analysis indicated that the amount of Na + -K + -ATPase protein had increased 2.1-fold in crabs acclimated 3 wk to DSW; however, 4 h after DSW transfer no difference in the amount of Na + -K + -ATPase protein was observed. After DSW transfer branchial cAMP content decreased. A negative correlation between branchial Na + -K + -ATPase activity and cAMP content points to rapid regulation of Na + -K + -ATPase through cAMP-dependent protein kinase A activity. Ca 2+ transport may depend on the high-capacity Na + /Ca 2+ exchanger coupled to the versatile sodium pump.