ABSTRACT
The aim of this study was to express the cloned skate anion exchanger 1 (skAE1) in Xenopus oocytes and determine whether the differences in monovalent cation permeabilities in hypotonically stimulated skate and trout erythrocytes could be due to differences in the presence or absence of intracellular channel regulators between the two species or in the intrinsic permeability properties of the channels themselves. The expressed protein (skAE1) was inserted into the oocyte cell membrane and facilitated both Cl- exchange and taurine transport. Expression of skAE1 in oocytes showed similar monovalent cation permeabilities as previously reported for skate erythrocytes and different from both trout erythrocytes and trAE1 expressed in Xenopus oocytes. These results show that the skAE1 expressed in oocytes functions in a manner similar to that of the osmolyte channel in hypotonically activated skate erythrocytes and supports the hypothesis that differences in the monovalent cation permeabilities of the osmolyte channels in skate and trout RBCs resides in the differences in permeability properties of the channels between the two species.
Subject(s)
Anion Exchange Protein 1, Erythrocyte/physiology , Cell Membrane Permeability/physiology , Chlorine/metabolism , Erythrocyte Membrane/physiology , Ion Channels/physiology , Oocytes/physiology , Taurine/metabolism , Animals , Cloning, Molecular , Recombinant Proteins/metabolism , Rubidium/metabolism , Skates, Fish , Sodium/metabolism , Species Specificity , Trout , Water-Electrolyte Balance/physiology , Xenopus laevisABSTRACT
During cell swelling, cells release organic osmolytes via a volume-activated channel as part of the regulatory volume decrease. The erythrocyte membrane protein AE1 (band 3), has been shown to be involved in regulatory volume responses of fish erythrocytes. Previous studies showed that the expression of trout AE1 in Xenopus laevis oocytes induces band 3 anion exchange activity and organic osmolyte channel activity. However, an endogenous swelling-activated anion channel, IClswell, is present in Xenopus oocyte membranes. Therefore, it is not yet known whether a new organic osmolyte channel is formed or whether the endogenous channel, IClswell, is activated when trout AE1 is expressed in the oocytes. The purpose of this study was to determine whether the expression of trout AE1 in Xenopus oocytes leads to the formation and membrane insertion of a new organic osmolyte channel or activates IClswell. To differentiate between the two possibilities, we compared the time courses, pH profiles and inhibitor sensitivities of both trout AE1 and IClswell. The results of taurine-uptake experiments show that the time courses and pH levels for optimum expression of trout AE1 and IClswell differ significantly. The inhibitor sensitivities of the organic osmolyte channel mediated by trout AE1 and IClswell are also significantly different, strongly suggesting that the expression of trout AE1 in Xenopus oocytes does not activate IClswell, but rather forms a new organic osmolyte channel.
