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Absence of Na + /K + /2Cl − cotransporter activity in corneal endothelial cell plasma membrane vesicles
Author(s) -
Lane Jason R.,
Wigham Chris G.,
Hodson Stuart A.
Publication year - 1997
Publication title -
ophthalmic and physiological optics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.147
H-Index - 66
eISSN - 1475-1313
pISSN - 0275-5408
DOI - 10.1046/j.1475-1313.1997.97807429.x
Subject(s) - cotransporter , vesicle , chemistry , biophysics , membrane , corneal endothelium , symporter , intracellular , endothelial stem cell , cell membrane , endothelium , biochemistry , sodium , biology , endocrinology , transporter , in vitro , organic chemistry , gene
There are various models to describe coupling between transmembrane Na − flux and transendothelial net HCO − 3 flux in the cornea, including a direct coupling via a Na + /HCO − 3 cotransporter or an indirect coupling utilizing a Na + /K + /2Cl − cotransporter further coupled to a Cl − /HCO − 3 exchanger. In this study we investigate the presence of Na + /K + /2Cl − cotransporter activity by using corneal endothelial cell plasma membrane vesicles. By controlling the external and internal compartments of the vesicles we were able to monitor Na + movement across the membranes. If the Na + /K + /2Cl − cotransporter is present in the corneal endothelial cell membrane vesicles then the presence of K + should lead to a significant increase in uptake of 22 Na + . The rate of accumulation of 22 Na + in the presence of K + was 25.7 ± 2.8 nmoles Na + mg −1 protein 15 s −1 which was not significantly different from that in the absence of K + (23.8 ± 2.0 nmoles Na + mg −1 protein 15 s −1 ) indicating that Na + uptake into the vesicles was not dependent on K + . The present work provides no evidence for Na + /K + /2Cl − cotransport in corneal endothelial cell plasma membrane vesicles. The nature of the coupling mechanism between HCO − 3 and Na + is still unresolved.