Characterization of cell ion exchange in the sea anemoneCondylactis gigantea |
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Authors: | Francisco C Herrera Arlec Rodriguez Ildemaro López Henny Weitzmann I Perey Zanders |
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Institution: | (1) Laboratorio de Ecofisiología Animal, Centro de Biofisica y Bioquímica, Instituto Venezolano de Investigaciones Centificas, Apartado 1827, 1010A Caracas, Venezuela |
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Abstract: | Summary Maintenance of intracellular ion contents and their relations to transmembrane potential were studied in tentacles ofCondylactis gigantea. Tentacles leached at 2°C in 10 mMK+ and 2 mM K+ artificial seawaters (10K ASW and 2K ASW) with and without 2 MM ouabain, and in 0K ASW, lost cell K+ and gained Na+. Rewarming to 25°C in 10K ASW resulted in a marked accumulation of K+ and extrusion of Na+ in tentacles leached in 10K ASW and in 0K ASW. Initial rate of Na+ extrusion was twice the initial rate of K+ accumulation, suggesting a pump coupling ratio of 2. In tentacles leached and rewarmed in 2K ASW, no net reaccumulation of K+ and little net extrusion of Na+ was observed; i.e., the pump just kept pace with the leaks. Ouabain inhibited K+ reaccumulation and Na+ extrusion. This effect was less marked in 10K ASW than in 2K ASW confirming, in anemone tentacles, the well documented ouabain-K+ antagonism observed in other systems. In no case did K
i
+
/K
0
+
equal Cl
0
–
/Cl
i
–
; therefore, the distribution of these ions did not fit a Donnan distribution. Transmembrane potential difference was –22±3 mV in 10K ASW at 25°C. It fitted a modified Nernst equation which includes the pump coupling ratio and a Na+ to K+ permeability ratio of 0.31.A moderately high permeability of the cell membrane to Na+, and a ouabain and K+ sensitive ion pump, exchanging 2 Na+ for 1 K+, appear to be responsible for the observed ionic distribution and transmembrane potential in anemone cells. |
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