Role of external calcium in sodium and chloride transport in the gills of seawater-adaptedMugil capito |
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Authors: | Pierre Pic and Jean Maetz |
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Institution: | (1) Groupe de Biologie Marine du Départment de Biologie du Commissariat à l'Energie Atomique, F-06230 Villefranche-sur-Mer, France;(2) Station Marine d'Endoume, rue Batterie des Lions, F-13007 Marseille, France |
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Abstract: | Summary When the mulletMugil capito is transferred to medium lacking Ca++ (either Ca++-free seawater or distilled water) the passive permeability of the gill to Na+ and Cl– is increased and the activating effect of external K+ on the Na+ and Cl– effluxes in hyposaline media is inhibited. The permeability of the gill increases progressively in proportion to the time of Ca++ deprivation; it declines when Ca++ is added again to the external medium. The active mechanisms for ion excretion are not reversible. At external Ca++ concentrations from 0.1 to 10 mM the Na+ permeability is constant but the activation of Na+ efflux by K+ shows a maximum at a Ca++ concentration of about 1 mM. For activation of Cl– efflux external bicarbonate must be present, in addition to Ca++, suggesting the existence of a Cl–/HCO
3
–
exchange. The mechanism by which Ca++ controls the passive branchial permeability is thus probably different from that involved in K+ activation of ion excretion. The Ca++ effect on the K+ sensitive ionic excretory mechanisms seems to be related to intracellular Ca++ movements. Thus, on the one hand, substances such as Ruthenium Red and La+++ which both inhibit Ca++ exchange, in media containing Ca++ and HCO
3
–
also inhibit K+ activation of Na+ and Cl– effluxes; on the other hand, the ionophore A 23187, a stimulator of Ca++ exchange, when added to these media, activates the Na+ and Cl– effluxes; its maximal effect on the Na+ flux occurs at 2 mM Ca++.Abbreviations
ASW-Ca
artificial seawater minus calcium
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DW
deionised water
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DWCa
deionised water with 1 mM Ca++ added
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DWCaHCO
3
DW with calcium plus bicarbonate
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DWHCO
3
DW with 1 mM sodium bicarbonate added
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FW
freshwater (tap water)
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FWK
freshwater with K+ added
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P. D.
potential difference
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SW
seawater
The experiments reported in this paper were done with Jean Maetz who tragically died in August 1977. It is the last report about several years of friendly collaboration |
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