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Am J Physiol Regul Integr Comp Physiol 270: R61-R70, 1996;
0363-6119/96 $5.00
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AJP - Regulatory, Integrative and Comparative Physiology, Vol 270, Issue 1 61-R70, Copyright © 1996 by American Physiological Society

ARTICLES

Swelling-activated K+ transport via two functionally distinct pathways in eel erythrocytes

J. D. Bursell and K. Kirk
University Laboratory of Physiology, Oxford, United Kingdom.

Following osmotic swelling, erythrocytes from the European eel, Anguilla anguilla, underwent a regulatory volume decrease. This was prevented by replacement of Na+ with K+ in the suspending medium, consistent with a role for the (normally outward) electrochemical K+ gradient in the volume-regulatory response. The effect of cell swelling on K- transport in these cells was investigated using 86Rb+ as a tracer for K+. Osmotic swelling resulted in an increase in ouabain-insensitive K+ transport that was highest for cells in Cl- and Br- media but which was also significant in I- and NO3- media. Treatment of eel erythrocytes suspended in isotonic Cl- or Br- (but not I- or NO3-) media with the sulfhydryl reagent N-ethylmaleimide (NEM) resulted in a large increase in K+ transport. A quantitative comparison of the pharmacological properties of the "Cl(-)-dependent" NEM-activated pathway with those of the "Cl(-)-independent" pathway mediating swelling-activated K+ transport in cells in Cl(-)-free (NO3- containing) media showed there to be significant differences between them. By contrast, the pharmacological properties of the Cl(-)-independent swelling-activated K+ pathway were indistinguishable from those of the pathway responsible for the swelling-activated transport of taurine, the major organic osmolyte in these cells. A pharmacological analysis of ouabain-insensitive K+ transport in cells swollen in a hypotonic Cl(-)-containing medium showed there to be two components, one with the characteristics of the NEM-activated system, the other showing the characteristics of the Cl(-)-independent swelling-activated pathway. The data are consistent with the presence of two functionally distinct swelling-activated K+ transport mechanisms in eel erythrocytes: a KCl cotransporter that is activated under isotonic conditions by NEM and a Cl(-)-independent, broad-specificity channel that accommodates a diverse range of organic and inorganic solutes.


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