Na(+)-dependent Ca2+ uptake in isolated opercular epithelium of Fundulus heteroclitus.
It is concluded that Ca2+ transport across the basolateral membranes of the ionocytes in killifish skin is mediated for the major part by a Na+/Ca(2+)-exchange mechanism that is driven by the (transmembrane) Na+ gradient established by Na+/K(+)-ATPase. The conclusion is based, firstly, on the biochemical evidence for the presence of a Na+/Ca(2+)-exchanger next to the Ca(2+)-ATPase in the basolateral membranes of killifish gill cells. Secondly, the transcellular Ca2+ uptake measured in an Ussing chamber setup was 85% and 80% reduced in freshwater (FW) and SW (SW) opercular membranes, respectively, as the Na+ gradient across the basolateral membrane was directly or indirectly (by ouabain) reduced. Thapsigargin or dibutyryl-cAMP/IBMX in SW opercular membranes reduced Ca2+ influx to 46%, comparable to the effects seen in FW membranes [reduction to 56%; Marshall et al. 1995a]. Basal Ca2+ influx across the opercular membrane was 48% lower in membranes from fish adapted to SW than in membranes from fish adapted to FW. Branchial Na+/K(+)-ATPase activity was two times higher in SW adapted fish.
Verbost
P M
PM
Department of Animal Physiology, Faculty of Science, University of Nijmegen, The Netherlands.
Bryson
S E
SE
Bonga
S E
SE
Marshall
W S
WS
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000222:Adaptation, Physiological / Q000502:physiology; D000818:Animals; D001692:Biological Transport; D003994:Bucladesine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005618:Fresh Water; D005880:Gills / Q000378:metabolism*; D007695:Killifishes / Q000378:metabolism*; D008297:Male; D008566:Membranes / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D012623:Seawater; D012964:Sodium / Q000378:metabolism; D019831:Sodium-Calcium Exchanger; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D019284:Thapsigargin / Q000494:pharmacology; D014638:Vanadates / Q000494:pharmacology
D002352:Carrier Proteins; D002712:Chlorides; D004791:Enzyme Inhibitors; D010726:Phosphodiesterase Inhibitors; D019831:Sodium-Calcium Exchanger; D014638:Vanadates; D010042:Ouabain; D003994:Bucladesine; D019284:Thapsigargin; D012964:Sodium; D000252:Calcium-Transporting ATPases; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium; D015056:1-Methyl-3-isobutylxanthine