A bicarbonate-dependent process inhibitable by disulfonic stilbenes and a Na+/H+ exchange mediate 22Na+ uptake into cultured bovine corneal endothelium

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Item Type:	Article
Title:	A bicarbonate-dependent process inhibitable by disulfonic stilbenes and a Na+/H+ exchange mediate 22Na+ uptake into cultured bovine corneal endothelium
Creators Name:	Jentsch, T.J., Stahlknecht, T.R., Hollwede, H., Fischer, D.G., Keller, S.K. and Wiederholt, M.
Abstract:	22Na+ uptake into confluent monolayers of cultured bovine corneal endothelial cells was studied in the presence of ouabain (10(-4)M) to inhibit active sodium extrusion. In bicarbonate saline, uptake was reduced to a similar degree either by amiloride (10(-3)M) or by 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) (10(-3)M). A further reduction was obtained with SITS-pretreated cells in the presence of amiloride. SITS-sensitive uptake was further characterized in saline containing both ouabain (10(-4)M) and amiloride (10(-3)M). It was absolutely dependent on bicarbonate, which could not be substituted by other plasma membrane permeable buffers (50 mM acetate or 25 mM glycodiazine). It was a saturable function of both bicarbonate and sodium concentration. Half-maximal fluxes occurred between 3 and 7 mM HCO3 (at 151 mM Na) and between 35 and 60 mM Na (at 28 mM HCO3). Uptake into sodium-depleted cells was reduced as opposed to sodium-rich cells, and SITS-sensitive 22Na+ efflux out of 22Na+-loaded cells into sodium-free medium was less than efflux into sodium saline, indicating trans-stimulation by sodium. The amiloride-sensitive pathway was studied in the absence of bicarbonate to inhibit uptake via the SITS-sensitive pathway. 22Na+ uptake into sodium-depleted cells increased steeply with extracellular pH in the range between pH 6 and 8 and could be largely blocked by 10(-3), but not by 10(-5) M amiloride. It is concluded that bovine corneal endothelial cells possess at least two distinct pathways for sodium uptake, amiloride sensitive 22Na+ fluxes being mediated by a Na+/H+ antiport, while the SITS-sensitive process is probably identical to a bicarbonate-sodium cotransport system postulated earlier from electrophysiological studies.
Keywords:	4-Acetamido-4'-Isothiocyanatostilbene-2,2'-Disulfonic Acid, Amiloride, Bicarbonates, Carrier Proteins, Cultured Cells, Cornea, Endothelium, Hydrogen-Ion Concentration, Ouabain, Sodium, Sodium-Hydrogen Antiporter, Stilbenes, Animals, Cattle
Source:	Journal of Biological Chemistry
ISSN:	0021-9258
Publisher:	American Society for Biochemistry and Molecular Biology
Volume:	260
Number:	2
Page Range:	795-801
Date:	25 January 1985
Official Publication:	http://www.jbc.org/content/260/2/795.abstract
PubMed:	View item in PubMed

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