Cellular and transepithelial responses of goldfish intestinal epithelium to chloride substitutions |
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Authors: | T Zuidema J W van Riel J Siegenbeek van Heukelom |
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Institution: | (1) Department of Zoology, Membrane Biophysics, University of Amsterdam, 1098 SM Amsterdam, The Netherlands |
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Abstract: | Summary In goldfish intestine chloride was substituted by large inorganic anions (gluconate or glucuronate) either mucosally, serosally or bilaterally. Changes in intracellular activities of chloride (a
i
Cl–), sodium (a
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Na+) and potassium (a
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K+), pHi, relative volume, membrane and transepithelial potentials, transepithelial resistance and voltage divider ratio were measured. Control values were:a
i
Cl–=35 meq/liter, a
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Na+=11 meq/liter and a
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K+=95 meq/liter. During bilateral substitution the latter two did not change while a
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Cl– dropped to virtually zero.Mucosal membrane potentials (ms) were: control,-53 mV; serosal substitution,-51 mV; bilateral substitution,-66 mV; while during mucosal substitution a transient depolarization occurred and the final steady state ms was-66 mV.During control and bilateral substitution the transepithelial potentials (ms) did not differ from zero. During unilateral substitutions ms was small, in the order of magnitude of the errors in the liquid junction potentials near the measuring salt bridges.During bilateral substitution pH
i
increased 0.4 pH units. Cellular volume decreased during mucosal substitution to 88% in 40 min; after serosal substitution it transiently increased, but the new steady-state value was not significantly above its control value.Three minutes after mucosal substitution ana
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Cl– of approx. 10 meq/liter was measured.Chemical concentrations of Na, K and Cl were determined under control conditions and bilateral substitution. Cl concentrations were also measured as a function of time after unilateral substitutions.The data indicate an electrically silent chloride influx mechanism in the brush border membrane and an electrodiffusional chloride efflux in the basolateral membrane. A substantial bicarbonate permeability is present in the basolateral membrane. The results are in agreement with the observed changes in membrane resistances, volume changes and pH changes. |
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Keywords: | intracellular ion activity K+ Na+ Cl– HCO
3
– intestinal epithelium intercellular space goldfish |
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