Mechanisms of zinc uptake in gills of freshwater rainbow trout: interplay with calcium transport.
The uptake mechanism of Zn2+ through the gill epithelium of freshwater rainbow trout was investigated both in intact animals and in isolated basolateral membranes. Involvement of the apical Ca2+ uptake sites in Zn2+ uptake was examined in vivo by pharmacological manipulation of the apical Ca2+ permeability. The apical entries of Ca2+ and Zn2+, but not Na2+ and Cl-, were inhibited by addition of La to the water. Addition of 1.0 microM La reduced the influxes of Ca2+ and Zn2+ to 22 +/- 3 and 53 +/- 7% (mean +/- SE) of the control value, respectively. Injection of CaCl2 also reduced the branchial influxes of Ca2+ and Zn2+. This treatment decreased the influx of Ca2- to 45 +/- 4% of the control level and the Zn2+ influx to 68 +/- 5%. These results strongly imply that Zn2+ passes across the apical membrane of the chloride cells of the gills via the same pathway as Ca2+. The presence of an active basolateral transporter for Zn2+ was investigated in vitro on isolated basolateral membranes. There was no ATP-dependent or Na2+(-)gradient driven transport of Zn2+ at physiological Zn2+ activities. The same system was used to study potential effects of Zn2+ on the basolateral Ca2+(-)adenosinetri-phosphatase. Zn2+ was found to be a potent blocker of this transporter, causing a mixed inhibitory effect on the ATP driven Ca2+ transport at a free Zn2+ activity of 100 pM.
Hogstrand
C
C
T. H. Morgan School of Biological Sciences, University of Kentucky, Lexington 40506-0225, USA.
Verbost
P M
PM
Bonga
S E
SE
Wood
C M
CM
D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D005880:Gills / Q000378:metabolism*; D007811:Lanthanum / Q000494:pharmacology; D017686:Oncorhynchus mykiss / Q000378:metabolism*; D015032:Zinc / Q000493:pharmacokinetics*
D002121:Calcium Channel Blockers; D007811:Lanthanum; D015032:Zinc; D002118:Calcium