Chloride current activated by swelling in retinal pigment epithelium cells

1993 ◽  
Vol 265 (4) ◽  
pp. C1037-C1045 ◽  
Author(s):  
L. M. Botchkin ◽  
G. Matthews
Keyword(s):  
Retinal Pigment Epithelium ◽  
Fluid Transport ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Ionic Composition ◽  
Cell Swelling ◽  
Disulfonic Acid ◽  
Subretinal Space ◽  
Channel Blockers ◽  
Membrane Stretch

A membrane conductance activated by cell swelling was characterized in cells of the retinal pigment epithelium (RPE). Manipulations of internal and external Cl concentration revealed that the conductance is permeable to Cl and somewhat permeable to the gluconate anion used for Cl substitution (ratio of gluconate to Cl permeability approximately 0.1). The conductance was blocked by the Cl channel blockers 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid and 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid in a manner consistent with open-channel blockade. Both the onset and recovery of the Cl current following a transient increase in cell volume were slow. This suggests that activation of the current depends on some internal signal rather than directly on membrane stretch. Experiments to examine a possible role for intracellular Ca concentration ([Ca]i) in regulation of the current demonstrated that an increase in [Ca]i was not involved in the linkage between swelling and Cl current; activation of the current was unaffected by the calcium-buffering conditions, the current could not be activated by large increases in [Ca]i elicited by ionomycin, and no changes in [Ca]i were observed to be associated with swelling. RPE cells normally experience changes in the volume and ionic composition of the extracellular subretinal space during changes in illumination conditions; therefore, the volume-sensitive Cl conductance may play a role in volume regulation in the RPE in response to these extracellular changes and/or in transepithelial fluid transport.

Potassium-induced chloride secretion across the frog retinal pigment epithelium

1994 ◽  
Vol 266 (4) ◽  
pp. C957-C966 ◽  
Author(s):  
J. L. Edelman ◽  
H. Lin ◽  
S. S. Miller
Keyword(s):  
Retinal Pigment Epithelium ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Basolateral Membrane ◽  
Chloride Secretion ◽  
Ringer Solution ◽  
Open Circuit ◽  
Disulfonic Acid ◽  
Subretinal Space ◽  
K Concentration

In the intact eye, a transition from light to dark increases K concentration ([K]o) from approximately 2 to 5 mM in the extracellular (subretinal) space between the photoreceptors and the retinal pigment epithelium (RPE) apical membrane. In control (HCO3/CO2) Ringer solution, 36Cl was actively absorbed across isolated bullfrog RPE (retina to choroid) at a rate of 0.31 +/- 0.02 (SE) mu eq.cm-2.h-1 (n = 15). Elevating apical [K]o from 2 to 5 mM reversed active 36Cl transport to secretion (choroid to retina), with a rate of 0.76 +/- 0.17 mu eq.cm-2.h-1. This reversal was completely inhibited by 1 mM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) in either the apical or basal bath. In open circuit, elevating [K]o induced a similar reversal of net 36Cl flux and inhibited fluid absorption by approximately 25%. Apical Ba2+ (1 mM), decreased CO2 (5 to 1%), or increased apical bath HCO3 concentration ([HCO3]o) also caused a DIDS-inhibitable reversal of active 36Cl flux. A 10-fold reduction of apical bath Na or [HCO3]o significantly inhibited [K]o, Ba2+, and low CO2-induced Cl secretion. All of these results can be understood in terms of an intracellular pH-dependent stimulation of the basolateral membrane Cl-HCO3 exchanger.

pHi-dependent Cl-HCO3 exchange at the basolateral membrane of frog retinal pigment epithelium

1994 ◽  
Vol 266 (4) ◽  
pp. C935-C945 ◽  
Author(s):  
H. Lin ◽  
S. S. Miller
Keyword(s):  
Retinal Pigment Epithelium ◽  
Initial Rate ◽  
Apical Membrane ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Basolateral Membrane ◽  
Ringer Solution ◽  
Disulfonic Acid ◽  
Subretinal Space ◽  
K Concentration

Intracellular pH (pHi) measurements in frog retinal pigment epithelium using the pH-sensitive dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein demonstrate that the basolateral membrane contains a pHi-sensitive Cl-HCO3 exchanger. In control Ringer solution, the removal of Cl from the basal bath alkalinized the cells by 0.07 +/- 0.03 (SD) pH units (n = 39) with an initial rate of 0.022 +/- 0.0013 pH units/min. This effect was blocked by 0.5 mM basal 4,4'-diisothiocyanostilbene-2,2'- disulfonic acid or the removal of HCO3 from both the apical and basal baths. The rate of the exchange is reduced by acidification and increased by alkalinization. Increasing apical bath K concentration ([K]o) from 2 to 5 mM approximates the [K]o change in the subretinal space of the intact eye following a transition from light to dark. This [K]o change alkalinized the cells by increasing the rate of the apical membrane Na-HCO3 cotransporter. In 5 mM apical [K]o, the initial rate of the 0 Cl-induced alkalinization was significantly increased to 304 +/- 13% (n = 4) of control (2 mM [K]o). These mechanisms regulate pHi and could also buffer changes in subretinal pH.

scholarly journals CO2-induced ion and fluid transport in human retinal pigment epithelium

2009 ◽  
Vol 133 (6) ◽  
pp. 603-622 ◽  
Author(s):  
Jeffrey Adijanto ◽  
Tina Banzon ◽  
Stephen Jalickee ◽  
Nam S. Wang ◽  
Sheldon S. Miller
Keyword(s):  
Retinal Pigment Epithelium ◽  
Fluid Transport ◽  
Apical Membrane ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Basolateral Membrane ◽  
Subretinal Space ◽  
Photoreceptor Outer Segments ◽  
Outer Segments

In the intact eye, the transition from light to dark alters pH, [Ca2+], and [K] in the subretinal space (SRS) separating the photoreceptor outer segments and the apical membrane of the retinal pigment epithelium (RPE). In addition to these changes, oxygen consumption in the retina increases with a concomitant release of CO2 and H2O into the SRS. The RPE maintains SRS pH and volume homeostasis by transporting these metabolic byproducts to the choroidal blood supply. In vitro, we mimicked the transition from light to dark by increasing apical bath CO2 from 5 to 13%; this maneuver decreased cell pH from 7.37 ± 0.05 to 7.14 ± 0.06 (n = 13). Our analysis of native and cultured fetal human RPE shows that the apical membrane is significantly more permeable (≈10-fold; n = 7) to CO2 than the basolateral membrane, perhaps due to its larger exposed surface area. The limited CO2 diffusion at the basolateral membrane promotes carbonic anhydrase–mediated HCO3 transport by a basolateral membrane Na/nHCO3 cotransporter. The activity of this transporter was increased by elevating apical bath CO2 and was reduced by dorzolamide. Increasing apical bath CO2 also increased intracellular Na from 15.7 ± 3.3 to 24.0 ± 5.3 mM (n = 6; P < 0.05) by increasing apical membrane Na uptake. The CO2-induced acidification also inhibited the basolateral membrane Cl/HCO3 exchanger and increased net steady-state fluid absorption from 2.8 ± 1.6 to 6.7 ± 2.3 µl × cm−2 × hr−1 (n = 5; P < 0.05). The present experiments show how the RPE can accommodate the increased retinal production of CO2 and H2O in the dark, thus preventing acidosis in the SRS. This homeostatic process would preserve the close anatomical relationship between photoreceptor outer segments and RPE in the dark and light, thus protecting the health of the photoreceptors.

Apical and basolateral membrane mechanisms that regulate pHi in bovine retinal pigment epithelium

1997 ◽  
Vol 273 (2) ◽  
pp. C456-C472 ◽  
Author(s):  
E. Kenyon ◽  
A. Maminishkis ◽  
D. P. Joseph ◽  
S. S. Miller
Keyword(s):  
Retinal Pigment Epithelium ◽  
Ph Regulation ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Basolateral Membrane ◽  
Disulfonic Acid ◽  
Cytosolic Ph ◽  
Acid Recovery ◽  
Tightly Coupled ◽  
Intracellular Microelectrodes

pH regulation was studied in fresh explant bovine retinal pigment epithelium-choroid using the pH-sensitive dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein and intracellular microelectrodes. Acid recovery was HCO3 dependent, inhibited by apical amiloride and apical or basal 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), and required apical and basal Na. Alkali recovery was HCO3 dependent and inhibitable by apical or basal DIDS. Three apical and two basolateral transporters were identified. Four contribute to acid extrusion, i.e., apical Na/H exchange, apical H-lactate cotransport, and apical Na-HCO3 cotransport and basolateral Na-HCO3 cotransport. At least two contribute to alkali extrusion, i.e., apical Na-HCO3 cotransport and a basolateral HCO3-dependent, DIDS-inhibitable mechanism, possibly Na-HCO3 cotransport, Cl/HCO3 exchange, or both. The apical Na-HCO3 cotransporter is electrogenic, carrying net negative charge inward. Basal Cl removal or addition of basal HCO3 caused HCO3- and Cl-dependent alkalinizations, respectively. Apical DIDS increased both responses. These cytosolic pH (pHi) regulatory mechanisms are so tightly coupled that changes in pHi can only occur after two or more of them are inhibited. In addition, these mechanisms help provide pathways for transport of Na and HCO3 across the retinal pigment epithelium between the blood and the distal retina.

Acidification stimulates chloride and fluid absorption across frog retinal pigment epithelium

1994 ◽  
Vol 266 (4) ◽  
pp. C946-C956 ◽  
Author(s):  
J. L. Edelman ◽  
H. Lin ◽  
S. S. Miller
Keyword(s):  
Retinal Pigment Epithelium ◽  
Short Circuit ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Basolateral Membrane ◽  
Short Circuit Current ◽  
Ringer Solution ◽  
Open Circuit ◽  
Disulfonic Acid ◽  
Fluid Absorption

Radioactive tracers and a modified capacitance-probe technique were used to characterize the mechanisms that mediate Cl and fluid absorption across the bullfrog retinal pigment epithelium (RPE)-choroid. In control (HCO3/CO2) Ringer solution, 36Cl was actively absorbed (retina to choroid) at a mean rate of 0.34 mu eq.cm-2.h-1 (n = 34) and accounted for approximately 25% of the short-circuit current. Apical bumetanide (100 microM) or basal 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS; 1 mM) inhibited active Cl transport by 70 and 62%, respectively. Active Cl absorption was doubled, either by removing HCO3 from the bathing media or by elevating CO2 from 5 to 13%, and the increased flux was inhibited by apical bumetanide or basal DIDS. Open-circuit measurements of fluid absorption rate (Jv) and the net fluxes of 36Cl, 22Na, and 86Rb (K substitute) indicated that CO2-induced acidification stimulated NaCl and fluid absorption across the RPE. During acidification, bumetanide produced a twofold larger inhibition of Jv compared with control. Stimulation of net Cl absorption was most likely caused by inhibition of the the basolateral membrane intracellular pH-dependent Cl-HCO3 exchanger.

The role of the retinal pigment epithelium in eye growth regulation and myopia: A review

2005 ◽  
Vol 22 (3) ◽  
pp. 251-261 ◽  
Author(s):  
JODI RYMER ◽  
CHRISTINE F. WILDSOET
Keyword(s):  
Retinal Pigment Epithelium ◽  
Growth Regulation ◽  
Fluid Transport ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Critical Role ◽  
Growth Modulation ◽  
Eye Growth ◽  
Retinal Growth ◽  
Growth Changes

Myopia is increasing in prevalence world-wide, nearing epidemic proportions in some populations. This has led to expanded research efforts to understand how ocular growth and refractive errors are regulated. Eye growth is sensitive to visual experience, and is altered by both form deprivation and optical defocus. In these cases, the primary targets of growth regulation are the choroidal and scleral layers of the eye that demarcate the boundary of the posterior vitreous chamber. Of significance to this review are observations of local growth modulation that imply that the neural retina itself must be the source of growth-regulating signals. Thus the retinal pigment epithelium (RPE), interposed between the retina and the choroid, is likely to play a critical role in relaying retinal growth signals to the choroid and sclera. This review describes the ion transporters and signal receptors found in the chick RPE and their possible roles in visually driven changes in eye growth. We focus on the effects of four signaling molecules, otherwise implicated in eye growth changes (dopamine, acetylcholine, vasoactive intestinal peptide (VIP), and glucagon), on RPE physiology, including fluid transport. A model for RPE-mediated growth regulation is proposed.

Lactate transport mechanisms at apical and basolateral membranes of bovine retinal pigment epithelium

1994 ◽  
Vol 267 (6) ◽  
pp. C1561-C1573 ◽  
Author(s):  
E. Kenyon ◽  
K. Yu ◽  
M. La Cour ◽  
S. S. Miller
Keyword(s):  
Retinal Pigment Epithelium ◽  
Short Circuit ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Basolateral Membrane ◽  
Open Circuit ◽  
Subretinal Space ◽  
Transport Mechanisms ◽  
Lactate Transport ◽  
Space Volume

The isolated bovine retinal pigment epithelium actively transports lactate from the apical to the basal bath. Net short-circuit [14C]lactate flux in 20 mM lactate was 0.46 +/- 0.09 mu eq.cm-2.h-1 (n = 8). In open circuit, with a physiological lactate gradient, net [14C]lactate flux was 0.66-1.31 mu eq.cm-2.h-1 (n = 3). Lactate in the apical bath caused intracellular acidifications that were saturable, apparently stereospecific, and reduced in magnitude by several H-lactate cotransport inhibitors. In the basal bath, lactate caused intracellular alkalinizations that were dependent on the presence of Na. In short circuit, 20 mM lactate in both baths reversed the direction of net transepithelial 22Na transport from secretion to absorption, suggesting the presence of basolateral Na-lactate cotransport moving lactate out of the cells. Outwardly directed Na-lactate cotransport requires a lactate:Na stoichiometry > 1.4:1, consistent with the coupled movement of Na, lactate, and net negative charge across the basolateral membrane. Intracellular microelectrode recordings showed that basal lactate hyperpolarized and apical lactate depolarized the basolateral membrane. For lactate absorption, this is a novel arrangement of membrane proteins:luminal H-lactate cotransport and serosal electrogenic Na:(n)lactate cotransport. Lactate transport across the retinal pigment epithelium may play an important role in regulating retinal metabolism and subretinal space volume and composition.

Sign in / Sign up

Export Citation Format

Share Document