Active ion transport pathways in the bovine retinal pigment epithelium.

Abstract

SUMMARY1. Radioactive tracer flux measurements demonstrate that active ion transport across the isolated bovine retinal pigment epithelium (RPE)-choroid preparation can be maintained for hours after the eye is enucleated and the tissue removed from the eye.2. It has been shown that 86Rb tracer fluxes can be used to monitor potassium (K+) transport across bull-frog RPE. In bovine RPE, net 86Rb (K+) absorption is zero. Apical barium (Ba2+) elevated active K+ absorption from zero to t 03 gequiv cm-2 h-1. This Ba2+-induced increase in active K+ absorption was inhibited either by ouabain or bumetanide in the apical bath.3. In control Ringer solution, buffered with bicarbonate and CO2' the RPEchoroid actively absorbs chloride (Cl-) at a rate of -05 /sequiv cm-2 h-1. In contrast, sodium (Na+) is secreted at a rate of 0O5 juequiv Cm-2 h-. Chloride absorption was inhibited by apical bumetanide, and Na+ secretion was inhibited by apical ouabain. These drugs were only effective when placed in the solution bathing the apical or retinal side of the tissue. 4. Net Cl-absorption requires an exit mechanism at the basolateral membrane. DIDS (4,4'-diisothiocyanostilbene-2,2'-disulphonic acid) in the basal bath completely inhibited net Cl-absorption in bicarbonate-free Ringer solution.5. These experiments show that the chloride transport pathway contains at least two components: (1) a bumetanide-sensitive uptake mechanism at the apical membrane; and (2) an efflux mechanism at the basolateral membrane that is blocked by DIDS.6. Three apical membrane mechanisms were identified that could help modulate[K+]0 in the subretinal or extracellular space that separates the distal retina and the RPE apical membrane. They are: (1) an ouabain-sensitive Na+-K+ pump; (2) a bumetanide-sensitive mechanism, the putative Na+-K+-Cl-co-transporter; (3) a barium-sensitive K+ channel that recycles, to the apical bath, most or all of the potassium that is actively taken up by the Na+-K+ pump and the co-transporter. 7. These data suggest that light-induced alterations in subretinal potassium that occur in vivo can activate the chloride transport pathway and help modulate RPE intracellular Cl-during transitions between the light and dark.MS 7720

Effects of KCNQ channel modulators on the M-type potassium current in primate retinal pigment epithelium

“…As a major route for K ϩ efflux across the basolateral C831 M-TYPE CURRENT IN THE RPE membrane, K ϩ channels play a key role in active K ϩ absorption (20), which, together with active Cl Ϫ absorption, promotes retinal adhesion by providing an important driving force for the absorption of subretinal fluid that lies between the rod and cone photoreceptors and the RPE (24). In native human RPE, the basolateral membrane potential is in the range Ϫ45 to Ϫ55 mV.…”

The delayed basolateral membrane hyperpolarization of the bovine retinal pigment epithelium: mechanism of generation.

“…1 suggests that the delayed basolateral membrane hyperpolarization (DBMH), which occurred during phase 2, could be generated by a change in Eci or gcl at the basolateral membrane. This possibility was confirmed using DIDS, which specifically blocks the RPE basolateral membrane Cl-conductance (Biagi, 1985;Miller & Edelman, 1990;Joseph & Miller, 1991;Bialek & Miller, 1994 (Bialek & Miller, 1994 and then increased by 6 + 2 Q cm2 in the steady state; a decreased by 42 + 12%. Figure 2B illustrates the effect of decreasing C02 from 5 to 1 %, which had the opposite effect on a'c, VA, Rt and a.…”

“…Since the osmolarities of the low-Cl-solutions were 20 mosmol F' higher than the control solutions, 20 mm mannitol was added to all other control solutions in the C-removal experiments to prevent possible made by substituting 10 mm Hepes buffer and 13 mm NaCl for NaHCO3. The presence of glutathione (1 mM) in both apical and basal perfusion solutions significantly increased the longevity of the RPE explant preparation as measured by the maintenance of several membrane transport, voltage and resistance parameters (Miller & Edelman, 1990;Joseph & Miller, 1991). Solutions containing HC03-were equilibrated with 5% C02-10% 02-85% N2.…”

Trafficking to the Apical and Basolateral Membranes in Polarized Epithelial Cells

“…Cell Type-Specific Variations in Sorting The Na,K-ATPase localizes to the apical membranes of cells of the retinal pigment epithelium (RPE) [113][114][115][116] and the choroid plexus. [117][118][119][120] Although these cells exhibit an apical distribution of this canonical basolateral protein, other proteins that serve as standard apical and basolateral markers retain their characteristic distributions.…”