Na(+) and Ca(2+) pumps in the gills, epipodites and branchiostegites of the european lobster Homarus gammarus: effects of dilute sea water.
Crude homogenates and plasma-membrane-enriched fractions were prepared from the epithelium of the gills, epipodites and branchiostegites of intermoult European lobsters Homarus gammarus, and Na(+)/K(+)-ATPase, Ca(2+)-ATPase and Na(+)/Ca(2+) exchange activities were quantified in these tissues. Lobsters were kept in sea water (salinity 35 ) or were adapted to dilute sea water (22.1 ). The lobster hyperregulates haemolymph osmolarity and Ca(2+) levels in both media. Homogenates of the podobranchs, arthrobranchs and pleurobranchs had comparable Na(+)/K(+)-ATPase specific activities, and mean activities increased significantly for all three types of gills when the animals were kept in dilute sea water. In the epipodites and branchiostegites, Na(+)/K(+)-ATPase specific activities exceeded those in the gills, and exposure to dilute sea water greatly enhanced these activities. In sea water, 80 % of the total Na(+)/K(+)-ATPase activity is associated with the gills and epipodites (each tissue containing 40 %) and 20 % with the branchiostegites; in dilute sea water, the gills contained approximately 25 %, the epipodites 40 % and the branchiostegites approximately 35 % of the total activity, indicating the relative importance of the epipodites and branchiostegites for ionic hyperregulation in dilute media. In plasma membrane vesicles isolated from the gills, epipodites and branchiostegites, Ca(2+) transport driven by ATP and by a Na(+ )gradient was demonstrated. Exposure to dilute sea water enhanced Na(+)/Ca(2+ )exchange and Ca(2+)-ATPase activities in the epipodites and branchiostegites; in the gills, however, Ca(2+) transport activities decreased. The role of these tissues and enzymes in Na(+) and Ca(2+) handling by the lobster is discussed.
Flik
G
G
Department of Animal Physiology, Faculty of Science, University of Nijmegen, Toernooiveld 1 6525 ED Nijmegen, The Netherlands, Montpellier II, Place Eugène Bataillon, France. gertflik@sci.kun.nl
Haond
C
C
D000818:Animals; D001934:Branchial Region / Q000201:enzymology; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002462:Cell Membrane / Q000201:enzymology; D004848:Epithelium / Q000201:enzymology; D005260:Female; D005880:Gills / Q000201:enzymology*; D008121:Nephropidae / Q000201:enzymology*; D012623:Seawater / Q000737:chemistry; D019831:Sodium-Calcium Exchanger / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
D019831:Sodium-Calcium Exchanger; D000252:Calcium-Transporting ATPases; D000254:Sodium-Potassium-Exchanging ATPase