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Am J Physiol Regul Integr Comp Physiol 276: R490-R499, 1999;
0363-6119/99 $5.00
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Vol. 276, Issue 2, R490-R499, February 1999

Na+-K+-ATPase and Na+/Ca2+ exchange activities in gills of hyperregulating Carcinus maenas

Cedomil Lucu and Gert Flik

Department of Animal Physiology, Faculty of Science, University of Nijmegen, 6525 ED Nijmegen, The Netherlands; and Center for Marine Research, Institute Rudjer Boskovic, 52210 Rovinj, Croatia

Na+-K+-ATPase and Na+/Ca2+ exchange activities were studied in gills of Carcinus maenas in seawater (SW) and after transfer to dilute seawater (DSW). Carcinus hyperregulates its hemolymph osmolarity through active uptake of Na+, Cl-, and Ca2+. In DSW total Na+-K+-ATPase activity in posterior gills quadrupled; Na+/Ca2+ exchange specific activity was unaffected, and total activity increased 1.67-fold. Short-circuit current (Isc) in voltage-clamped posterior gill hemilamellae was -181 µA/cm2 in SW and -290 µA/cm2 in DSW and up to 90% ouabain sensitive; conductivity was similar in SW or DSW (42 and 46 mS/cm2, 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+/Ca2+ 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. Ca2+ transport may depend on the high-capacity Na+/Ca2+ exchanger coupled to the versatile sodium pump.

crab; sodium transport; ouabain; adenosine 3',5'-cyclic monophosphate


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