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, ionic
strength, and volume changes
Laboratoire J. Maetz, Département de Biologie Cellulaire et Moléculaire, Commissariat à l'Energie Atomique, and Unité de Recherche Associée 1855, Centre National de la Recherche Scientifique, 06238 Villefranche-sur-Mer Cedex, France
If swelling of a
cell is induced by a decrease in external medium tonicity, the
regulatory response is more complex than if swelling of similar
magnitude is due to salt uptake. The present results provide an
explanation. In fish erythrocytes, two distinct transport pathways were
swelling activated: a channel of broad specificity and a
K+-Cl
cotransporter. Each was activated by a specific signal: the channel by
a decrease in intracellular ionic strength and the
K+-Cl
cotransporter by cell enlargement. A decrease in ionic strength also
affected
K+-Cl
cotransport activity, but by acting as a negative modulator of the
cotransport. Thus cells swollen by salt accumulation respond by
activating exclusively the
K+-Cl
cotransport, leading to a
Cl
-dependent
K+ loss. By contrast, cells
swollen by electrolyte dilution respond by activating both pathways,
leading to a reduced loss of electrolytes and a large loss of taurine.
Thus two swelling-sensitive pathways, differently regulated, would
allow control of the ionic composition of a cell exposed to different
volume perturbations.
volume regulation; taurine; volume-activated transports; anion channel; potassium-chloride cotransport
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