Journal Title
Title of Journal: J Comp Physiol B
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Abbravation: Journal of Comparative Physiology B
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Publisher
Springer-Verlag
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Authors: J A Capo P K Mandal S Eyyunni G A Ahearn
Publish Date: 2004/11/23
Volume: 175, Issue: 1, Pages: 13-20
Abstract
The lobster Homarus americanus hepatopancreatic epithelial basolateral cell membrane possesses three transport proteins that transfer calcium between the cytoplasm and hemolymph an ATPdependent calcium ATPase a sodiumcalcium exchanger and a verapamilsensitive cation channel We used standard centrifugation methods to prepare purified hepatopancreatic basolateral membrane vesicles and a rapid filtration procedure to investigate whether 65Zn2+ transfer across this epithelial cell border occurs by any of these previously described transporters for calcium Basolateral membrane vesicles were osmotically reactive and exhibited a time course of uptake that was linear for 10–15 s and approached equilibrium by 120 s In the absence of sodium 65Zn2+ influx was a hyperbolic function of external zinc concentration and followed the MichaelisMenten equation for carrier transport This carrier transport was stimulated by the addition of 150 μM ATP increase in Km and Jmax and inhibited by the simultaneous presence of 150 μmol l−1 ATP+250 μmol l−1 vanadate decrease in both Km and Jmax In the absence of ATP 65Zn2+ influx was a sigmoidal function of preloaded vesicular sodium concentration 0 5 10 20 30 45 and 75 mmol l−1 and exhibited a Hill Coefficient of 403±114 consistent with the exchange of 3 Na+/1Zn2+ Using Dixon analysis calcium was shown to be a competitive inhibitor of basolateral membrane vesicle 65Zn2+ influx by both the ATPdependent Ki=205 nmol l−1 Ca2+ and sodiumdependent Ki=247 μmol l−1 Ca2+ transport processes These results suggest that zinc transport across the lobster hepatopancreatic basolateral membrane largely occurred by the ATPdependent calcium ATPase and sodiumcalcium exchanger carrier proteins
Keywords:
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