Presence and distribution of Na+/K+-ATPase in the ciliary epithelium of the rabbit

A renal-like organic anion transport system in the ciliary epithelium of the bovine and human eye

The purpose of this study was to determine the direction of organic anion (OA) transport across the ciliary body and the transport proteins that may contribute. Transport of several OAs across the bovine ciliary body was examined using ciliary body sections mounted in Ussing chambers and a perfused eye preparation. Microarray, reverse-transcription polymerase chain reaction (RT-PCR), immunoblotting, and immunohistochemistry were used to examine OA transporter expression in human ocular tissues. Microarray analysis showed that many OA transporters common to other barrier epithelia are expressed in ocular tissues. mRNA (RT-PCR) and protein (immunoblotting) for OAT1, OAT3, NaDC3, and MRP4 were detected in extracts of the human ciliary body from several donors. OAT1 and OAT3 localized to basolateral membranes of nonpigmented epithelial cells and MRP4 to basolateral membranes of pigmented cells in the human eye. Para-aminohippurate (PAH) and estrone-3-sulfate transport across the bovine ciliary body in the Ussing chambers was greater in the aqueous humor-to-blood direction than in the blood-to-aqueous humor direction, and active. There was little net directional movement of cidofovir. Probenecid (0.1 mM) or novobiocin (0.1 mM) added to the aqueous humor side of the tissue, or MK571 (5-(3-(2-(7-chloroquinolin-2-yl)ethenyl)phenyl)-8-dimethylcarbamyl-4,6-dithiaoctanoic acid; 0.1 mM) added to the blood side significantly reduced net active PAH transport. The rate of 6-carboxyfluorescein elimination from the aqueous humor of the perfused eye was reduced 80% when novobiocin (0.1 mM) was present in the aqueous humor. These data indicate that the ciliary body expresses a variety of OA transporters, including those common to the kidney. They are likely involved in clearing potentially harmful endobiotic and xenobiotic OAs from the eye.

Species variation in biology and physiology of the ciliary epithelium: similarities and differences

Glaucoma is a leading cause of irreversible blindness worldwide. Lowering intraocular pressure (IOP) is the only strategy documented to delay the appearance and retard the progression of vision loss. One major approach for lowering IOP is to slow the rate of aqueous humor formation by the ciliary epithelium. As discussed in the present review, the transport basis for this secretion is largely understood. However, several substantive issues are yet to be resolved, including the integrated regulation of secretion, the functional topography of the ciliary epithelium, and the degree and significance of species variation in aqueous humor inflow. This review discusses species differences in net secretion, particularly of Cl(-) and HCO(3)(-) secretion. Identifying animal models most accurately mimicking aqueous humor formation in the human will facilitate development of future novel initiatives to lower IOP.

The alpha1 isoform of the Na+/K+ ATPase is up-regulated in dedifferentiated progenitor cells that mediate lens and retina regeneration in adult newts

Adult newts are able to regenerate their retina and lens after injury or complete removal through transdifferentiation of the pigmented epithelial tissues of the eye. This process needs to be tightly controlled, and several different mechanisms are likely to be recruited for this function. The Na(+)/K(+) ATPase is a transmembrane protein that establishes electrochemical gradients through the transport of Na(+) and K(+) and has been implicated in the modulation of key cellular processes such as cell division, migration and adhesion. Even though it is expressed in all cells, its isoform composition varies with cell type and is tightly controlled during development and regeneration. In the present study we characterize the expression pattern of Na(+)/K(+) ATPase alpha1 in the adult newt eye and during the process of lens and retina regeneration. We show that this isoform is up-regulated in undifferentiated cells during transdifferentiation. Such change in composition could be one of the mechanisms that newt cells utilize to modulate this process.

Electron microprobe analysis of rabbit ciliary epithelium indicates enhanced secretion posteriorly and enhanced absorption anteriorly

The rate of aqueous humor formation sequentially across the pigmented (PE) and nonpigmented (NPE) ciliary epithelial cell layers may not be uniform over the epithelial surface. Because of the tissue's small size and complex geometry, this possibility cannot be readily tested by conventional techniques. Rabbit iris-ciliary bodies were divided, incubated, quick-frozen, cryosectioned, and freeze-dried for electron probe X-ray microanalysis of the elemental contents of the PE and NPE cells. We confirmed that preincubation with ouabain to block Na(+),K(+)-ATPase increases Na(+) and decreases K(+) contents far more anteriorly than posteriorly. The anterior and posterior regions were the iridial portion of the primary ciliary processes and the pars plicata, respectively. Following interruption of gap junctions with heptanol, ouabain produced smaller changes in anterior PE cells, possibly reflecting higher Na(+) or K(+) permeability of anterior NPE cells. Inhibiting Na(+) entry selectively with amiloride, benzamil, or dimethylamiloride reduced anterior effects of ouabain by approximately 50%. Regional dependence of net secretion was also assessed with hypotonic stress, which stimulates ciliary epithelial cell regulatory volume decrease (RVD) and net Cl(-) secretion. In contrast to ouabain's actions, the RVD was far more marked posteriorly than anteriorly. These results suggest that 1) enhanced Na(+) reabsorption anteriorly, likely through Na(+) channels and Na(+)/H(+) exchange, mediates the regional dependence of ouabain's actions; and 2) secretion may proceed primarily posteriorly, with secondary processing and reabsorption anteriorly. Stimulation of anterior reabsorption might provide a novel strategy for reducing net secretion.

Ciliary tissue transplantation in the rabbit

Irreversible damage of the ciliary body can be responsible for prolonged ocular hypotony and phthisis bulbi, which, currently, cannot be treated. The aim of this study was to achieve survival of morphologically normal ciliary tissue (CT) transplants in the anterior chamber of a rabbit's eye. Outbred female New Zealand albino rabbits received CT allografts, which were placed on to the surface of the host iris. We evaluated the influence of ciclosporin (CsA), VEGF and donor perfusion on graft survival. Operated eyes were assessed clinically and histologically, and revascularization of the grafts was determined by fluorescein angiography. All grafts became dark and ischemic during the first five to seven days after transplantation. Reperfusion of the grafted tissue was complete at approximately ten days after transplantation. In untreated animals, transplants became infiltrated by inflammatory cells, which led to destruction of the tissue. This was prevented by systemic use of CsA. Transplants treated with VEGF prior to transplantation had fewer ischemic areas but epithelial cell survival was not improved. Whole body donor perfusion prior to preparation of the grafts resulted in less inflammation and, histologically, in a better quantity and quality of the epithelial cells in the CT transplants. Ciliary tissue can be successfully transplanted but the ciliary epithelium suffers from ischemia and in untreated animals the whole transplant is rejected in the classical fashion. If the donor is perfused and the host immunosuppressed, histologically normal ciliary epithelium can be preserved together with rapid revascularization, minimal inflammation and good survival of the transplant, although fibrosis continued to occur during the two months after transplantation.

Cyclic GMP, sodium nitroprusside and sodium azide reduce aqueous humour formation in the isolated arterially perfused pig eye

The effect of nitric oxide (NO) on aqueous humour formation (AHF) and intraocular pressure (IOP) was studied using NO donors, sodium azide (AZ) and sodium nitroprusside (SNP). Using the porcine arterially perfused eye preparation, drug effects on AHF and IOP were measured by fluorescein dilution and manometry, respectively. Perfusion pressure of the ocular vasculature was also monitored using digital pressure transducer and pen recorder. L-Arginine (1.0 mM), a precursor of NO, but not D-arginine (1.0 mM), the inactive analogue, produced a significant reduction in AHF (28.5%) and IOP (21.1%). L-NAME (L-nitro-L-arginine) (10-100 microM), an NO synthase inhibitor, had no effect on AHF and IOP. However, L-NAME (100 microM) completely reversed L-arginine's effect. AZ and SNP reduced the AHF and IOP dose-dependently. AZ at 100 nM, 1 and 10 microM reduced AHF by 26.0, 39.7 and 51.7% and IOP by 10.8, 17.3 and 24.0%, respectively. SNP at 1, 10 and 100 microM reduced the AHF by 6.0, 24.2 and 35.4% and IOP by 3.5, 9.5 and 15.5%, respectively. 8-pCPT-cGMP (8-para-chlorophenyl-thioguanosine-3',5'-cyclic guanosine monophosphate, 10 microM), a cGMP analogue, also reduced the AHF (34.9%) and IOP (15.9%). The effects of AZ and SNP on the AHF and IOP were blocked by a soluble guanylate cyclase inhibitor ODQ (10 microM), whereas ODQ alone or combined with 8-pCPT-cGMP had no effect on the AHF and IOP. None of the drugs had any significant effect on ocular vasculature. The reduction of the AHF and IOP in the arterially perfused pig eye by nitrovasodilators is likely to involve the NO-cGMP pathway.

Basis of chloride transport in ciliary epithelium

The aqueous humor is formed by the bilayered ciliary epithelium. The pigmented ciliary epithelium (PE) faces the stroma and the nonpigmented ciliary epithelium (NPE) contacts the aqueous humor. Cl(-) secretion likely limits the rate of aqueous humor formation. Many transport components underlying Cl(-) secretion are known. Cl(-) is taken up from the stroma into PE cells by electroneutral transporters, diffuses to the NPE cells through gap junctions and is released largely through Cl(-) channels. Recent work suggests that significant Cl(-) recycling occurs at both surfaces of the ciliary epithelium, providing the basis for modulation of net secretion. The PE-NPE cell couplet likely forms the fundamental unit of secretion; gap junctions within the PE and NPE cell layers are inadequate to maintain constancy of ionic composition throughout the epithelium under certain conditions. Although many hormones, drugs and signaling cascades are known to have effects, a persuasive model of the regulation of aqueous humor formation has not yet been developed. cAMP likely plays a central role, potentially both enhancing and reducing secretion by actions at both surfaces of the ciliary epithelium. Among other hormone receptors, A(3) adenosine receptors likely alter intraocular pressure by regulating NPE-cell Cl(-) channel activity. Recently, functional evidence for the regional variation in ciliary epithelial secretion has been demonstrated; the physiologic and pathophysiologic implications of this regional variation remain to be addressed.

Neural regeneration in the chick retina

In warm-blooded vertebrates, possibilities for retinal regeneration have recently become reality with the discovery of neural stem cells in the mature eye. A number of different cellular sources of neural stem cells have been identified. These sources include stem cells at the retinal margin, pigmented cells in the ciliary body and iris, non-pigmented cells in the ciliary body and Müller glia within the retina. This review focuses on recent reports of neural stem cells and regeneration in the postnatal chicken retina. In the chicken eye sources of neurogensis and regeneration include: (1) retinal stem cells at the peripheral edge of the retina; (2) Müller glia in central regions of the retina; (3) non-pigmented epithelial cells in the posterior portion of the ciliary body; and (4) possibly pigmented cells in the pars plana of the ciliary body. This review discusses the similarities between the retinal progenitor cells in the postnatal eye and those found in the embryo. In addition, I discuss combinations of growth factors, (insulin, IGF-I, EGF and FGF2) that are capable of stimulating the proliferation and production of neurons from neural progenitors, non-neural epithelial cells, and postmitotic support cells in the avian eye. In summary, the mechanisms that regulate the proliferation and differentiation of cells with neurogenic potential are beginning to be understood and the postnatal chicken eye has proven to be a useful model system to study retinal regeneration.

The ins and outs of aqueous humour secretion

The intraocular pressure (IOP) reflects a balance between inflow and outflow of aqueous humour. A major strategy in the medical treatment of glaucoma is to reduce inflow and thereby IOP. Understanding the mechanisms and regulation of inflow is thus of clear clinical relevance. Many mechanisms underlying inflow have been identified. The integration and regulation of these mechanisms is less clear. Aqueous humour is secreted across the ciliary epithelium by transferring solute, chiefly NaCl, from the stroma to the posterior chamber of the eye, with water passively following. The epithelium consists of two layers: the pigmented ciliary epithelial (PE) cells abutting the stroma, and the non-pigmented ciliary epithelial (NPE) cells facing the aqueous humour. Gap junctions link adjacent cells within and between these layers. Secretion proceeds in three steps: (1) uptake of NaCl from stroma to PE cells by electroneutral transporters, (2) passage of NaCl from PE to NPE cells through gap junctions, and (3) release of Na+ and Cl- through Na+,K+-activated ATPase and Cl- channels, respectively. Most of our understanding of inflow mechanisms has been obtained by studying in vitro preparations at subcellular, cellular and tissue levels. A particularly productive approach has been the electron probe X-ray microanalysis (EPMA) of the elemental composition of excised ciliary epithelium. This technique permits analysis of adjacent cells within different regions of the ciliary epithelium. EPMA of rabbit preparations has supported the idea that paired activity of Na+/H+ and Cl-/HCO3- antiports can be the dominant mechanism underlying the first step in secretion, stromal NaCl uptake by PE cells. EPMA also indicates that Cl- turnover is faster in the anterior than the posterior region of the epithelium. At the opposite epithelial surface, release of Na+ through Na+,K+-activated ATPase of NPE cells is also greater anteriorly than posteriorly. The accompanying release of Cl- through ion channels is enhanced by agonists of A3 adenosine receptors (ARs). The concepts that paired antiport activity is important in stromal NaCl uptake and that A3ARs modulate NaCl release into the aqueous humour were based on in vitro studies. The potential relevance of these conclusions to in vivo conditions has been tested by measurements of IOP in the living mouse. The results have confirmed the predictions that inhibitors of Na+/H+ antiports lower IOP, and that A3AR agonists and antagonists raise and lower IOP, respectively.

Electron microprobe analysis of ouabain-exposed ciliary epithelium: PE-NPE cell couplets form the functional units

Aqueous humor is secreted by the bilayered ciliary epithelium. Solutes and water enter the pigmented ciliary epithelial (PE) cell layer, cross gap junctions into the nonpigmented ciliary epithelial (NPE) cell layer, and are released into the aqueous humor. Electrical measurements suggest that heptanol reduces transepithelial ion movement by interrupting PE-NPE communication and that gap junctions may be a regulatory site of aqueous humor formation. Several lines of evidence also suggest that net ciliary epithelial transport is strongly region dependent. Divided rabbit iris-ciliary bodies were incubated in chambers under control and experimental conditions, quick-frozen, cryosectioned, and freeze-dried. Elemental intracellular contents of NPE and PE cells were determined by electron probe X-ray microanalysis. With or without heptanol, ouabain produced concentration- and time-dependent changes more markedly in anterior than in posterior epithelium. Without heptanol, there were considerable cell-to-cell variations in Na gain and K loss. However, contiguous NPE and PE cells displayed similar changes, even when nearby cell pairs were little changed by ouabain in aqueous, stromal, or both reservoirs. In contrast, with heptanol present, ouabain added to aqueous or both reservoirs produced much larger changes in NPE than in PE cells. The results indicate that 1) heptanol indeed interrupts PE-NPE junctions, providing an opportunity for electron microprobe analysis of the sidedness of modification of ciliary epithelial secretion; 2) Na and K undergo faster turnover in anterior than in posterior epithelium; and 3) PE-NPE gap junctions differ from PE-PE and NPE-NPE junctions in permitting ionic equilibration between adjoining ouabain-stressed cells.

Growth factors induce neurogenesis in the ciliary body

The ciliary body of the eye is a nonneural tissue that is derived from the anterior rim of the optic cup, an extension of the neural tube. This tissue normally does not contain neurons and functions to produce components of the aqueous humor. We found that intraocular injections of insulin, EGF, or FGF2 stimulate NPE cells to proliferate and differentiate into neurons. These growth factors had region-specific effects along the radial axis of the ciliary body, with insulin and EGF stimulating proliferation of NPE cells close to the retina, while FGF2 stimulated the proliferation of NPE cells further toward the lens. Similar region-specific effects were observed for accumulations of neurons in the NPE in response to injections of different growth factors. The neurons derived from NPE cells express neurofilament, beta3 tubulin, RA4, calretinin, Islet1, or Hu, and a few produced long axonal projections, several millimeters in length that extend across the ciliary body. Our results suggest that the ciliary body has the capacity to generate retinal neurons, but normally neurogenesis is actively inhibited.

Fluid transport by human nonpigmented ciliary epithelial layers in culture: a homeostatic role for aquaporin-1

We report for the first time that cultured nonpigmented human ciliary epithelial (NPE) cell layers transport fluid. Cells were grown to confluence on permeable membrane inserts, and fluid transport across the resulting cell layers was determined by volume clamp at 37 degrees C. These cell layers translocated fluid from the apical to the basal side at a steady rate of 3.6 microl x h(-1) x cm(-2) (n = 4) for 8 h. This fluid movement was independent of hydrostatic pressure and was completely inhibited by 1 mM ouabain, suggesting it arose from fluid transport. Mercuric chloride, a nonspecific but potent blocker of Hg(2+)-sensitive aquaporins, and aquaporin-1 antisense oligonucleotides both partially inhibited fluid transport across the cell layers, which suggests that water channels have a role in NPE cell homeostasis. In addition, these results suggest that of the two ciliary epithelial layers in tandem, the NPE layer by itself can transport fluid. This cultured layer, therefore, constitutes an interesting model that may be useful for physiological and pharmacological characterization of ciliary epithelial fluid secretion.

Glycoconjugates of the rat ciliary body epithelium: a lectin histochemical and protein blotting study

The present study sought to identify and partially characterize the glycoconjugates specific to the double-layered ciliary body epithelium of the rat eye by lectin histochemistry and lectin blottings. Hydrated paraffin sections of Carnoy-fixed Sprague-Dawley rat eyes were stained with a panel of 21 different biotinylated lectins, followed by streptavidin-peroxidase and the glucose oxidase-diaminobenzidine-nickel staining procedure. The results of lectin histochemistry revealed that the inner epithelial layer was rich in GlcNAc(beta1,4)GlcNAc, alpha-Gal, Gal(beta1,3)GalNAc, GalNAc(alpha1,3)GalNAc/Gal, GalNAc(alpha1,6)Gal, Fuc(alpha1,2)Gal(beta1,4)GlcNAc and Gal(beta1,4)GlcNAc(beta1,2)Man(alpha1,6) sugar residues as shown by its positive reactivities with S-WGA, PWA, DSA, GS-I-B4, PNA, DBA, SBA, WFA, UEA-I, LTA and PHA-E. The reactivities of GS-I-B4, PNA, DBA and SBA were restricted to the inner layer at the tips of the ciliary processes. On the other hand, the outer epithelial layer was stained evenly by DSA and Jacalin, and partly by MAA, showing that this epithelial layer was rich in GlcNAc(beta1,4)GlcNAc, Gal(beta1,3)GalNAc and NeuAc(alpha2,3)Gal disaccharides. These lectin binding patterns of the ciliary body epithelium suggest a topographical and functional difference in this double cell-layered epithelium. Their possible roles in the secretion of aqueous humour and production of ciliary zonule are discussed. Some identified lectin markers specific to these two cell layers may be useful for further experimental studies. Glycoproteins extracted from the dissected ciliary body were separated by SDS-PAGE electrophoresis and analyzed by protein blottings with 8 different lectins. The results showed that at least 10 major membrane-bound glycoproteins, with molecular weights ranging from 30 to 150 kD, rich in beta-GlcNAc, beta-Gal, alpha/beta-GalNAc and NeuAc(alpha2,6)Gal residues, were present in the microsomal fraction.

Specialized neuropeptide Y- and glucagon-like immunoreactive amacrine cells in the peripheral retina of the turtle

There are many regional differences in cell morphology and neurochemistry in the retina. This study examined a specialized population of neuropeptide Y- and glucagon-like immunoreactive amacrine cells in the peripheral retina of the turtle. Some of the dendritic processes from these peptidergic amacrine cells formed a dense circumferentially oriented nerve fiber plexus which ran parallel to the ora serrata. Collaterals from this plexus projected into and innervated the nonpigmented ciliary epithelium in the pars plana region of the ciliary body. Electron microscopy revealed that the neuropeptide Y- and glucagon-like immunoreactive processes in the ciliary epithelium contained many labeled, large dense-cored vesicles. Small crystals of lipid-soluble fluorescent dye were implanted in the retina near the ora serrata in fixed retinal tissue to search for other peripheral retinal specializations. Numerous thick and thin cell processes oriented parallel to the ora serrata were labeled in the retina by the dye. In addition, many dye-labeled somata with circumferentially oriented dendritic arborizations were seen in the extreme periphery of the retina. Many of these dye-labeled cells and processes were clearly not associated with the neuropeptide Y- and glucagon-like immunoreactive cells described above. This study has shown that some peptidergic neurons in the peripheral retina have a unique morphology in comparison to more centrally located cells. The function of these specialized peripheral cells is not established, but the innervation of the ciliary epithelium by peptidergic amacrine cells suggests that they may be involved in control of aqueous inflow.

Vacuolar H+-ATPase in ocular ciliary epithelium

The mechanisms controlling the production of aqueous humor and the regulation of intraocular pressure are poorly understood. Here, we provide evidence that a vacuolar H+-ATPase (V-ATPase) in the ocular ciliary epithelium is a key component of this process. In intracellular pH (pHi) measurements of isolated ciliary epithelium performed with 2',7-biscarboxyethyl-5(6)-carboxyfluorescein (BCECF), the selective V-ATPase inhibitor bafilomycin A1 slowed the recovery of pHi in response to acute intracellular acidification, demonstrating the presence of V-ATPase in the plasma membrane. In isolated rabbit ciliary body preparations examined under voltage-clamped conditions, bafilomycin A1 produced a concentration-dependent decrease in short-circuit current, and topical application of bafilomycin A1 reduced intraocular pressure in rabbits, indicating an essential role of the V-ATPase in ciliary epithelial ion transport. Immunocytochemistry utilizing antibodies specific for the B1 isoform of the V-ATPase 56-kDa subunit revealed localization of V-ATPase in both the plasma membrane and cytoplasm of the native ciliary epithelium in both rabbit and rat eye. The regional and subcellular distribution of V-ATPase in specific regions of the ciliary process was altered profoundly by isoproterenol and phorbol esters, suggesting that change in the intracellular distribution of the enzyme is a mechanism by which drugs, hormones, and neurotransmitters modify aqueous humor production.

Characterization of bovine ciliary pigmented epithelial cells in monolayer culture: an ultrastructural, enzyme histochemical and immunohistochemical study

Monolayer cultures of the pigmented epithelial (PE) cells derived from two regions of the pars plicata of bovine eyes were established and grown up to the third passage. After this passage, the cultures became senescent. During the first three passages, the PE cells lost their pigment granules but developed a distinct cellular polarity by forming junctional complexes at their apical cell portions and depositing basement membrane like material on their basal side. The junctional complexes were shown to be impermeable for horseradish peroxidase, suggesting that they contained tight junctions. Histochemically, the monolayer cells stained for carbonic anhydrase (CA) and Na+/K(+)-ATPase, enzymes involved in active fluid secretion. Staining for CA and Na+/K(+)-ATPase as well as for acid phosphatase and immunostaining for vimentin and actin of the cultured PE cells were comparable with that of PE cells in vivo. Therefore, PE monolayer cultures are considered to be a suitable model for experimental studies in vitro.

Ciliary body degeneration in the Royal College of Surgeons dystrophic rat

We have studied the pathological changes of the ciliary body in Royal College of Surgeons (RCS) rats with an inherited retinal degeneration. Morphometric analyses were performed on sectioned ciliary bodies by a computerized morphometry system. Age-matched non-pigmented Sprague-Dawley (SD) rats were used as the control animals. The ciliary body of 26-day-old RCS dystrophic rats showed normal structure. However, the length and height of the pars plicata of the ciliary body became shorter and the area became smaller with increased age. Significant decreases in the values of these three parameters were observed between 26-day-old and 3-month-old RCS dystrophic rats. These parameters also showed significant differences when values of 3-month-old RCS dystrophic rats were compared to those of 3-month-old control SD rats. The same trends were observed in the ciliary body measurements in RCS dystrophic rats up to 1 year of age. Scanning electron microscopic examination demonstrated the progressive thinning of the pars plicata of the ciliary body with age in the RCS dystrophic rats. The total volume of the ciliary process of 6-month-old RCS dystrophic rats appeared to be one-half that of 26-day-old RCS dystrophic rats. Transmission electron microscopy revealed progressive cellular degenerative changes in the non-pigmented and pigmented ciliary epithelium of the RCS dystrophic rats. It was apparent that the pigmented ciliary epithelium had more severe degenerative changes than the non-pigmented ciliary epithelium. Immunostaining for Na+ + K+ ATPase of the ciliary epithelium was found to be less in the RCS dystrophic rats than in age-matched controls. This result suggests a possible dysfunction of ion transport in the ciliary body of the RCS dystrophic rats, which may account for their increased incidence of cataract formation. Although the mechanisms for the ciliary body degeneration in RCS dystrophic rats remain speculative, these findings add a new area of interest in this model of inherited retinal dystrophy.

Human ciliary body in organ culture

Ciliary body explants from 30 human eyes were maintained in organ culture up to 14 days. The age of the donors ranged from 45 to 85 years, the post mortem time from 4 to 22 hours. The ciliary epithelium as well as the underlying stroma were studied light- and electronmicroscopically before incubation and after 1, 3, 5, 7 and 14 days of culture. At the same time intervals, the localization of Na/K-ATPase and carbonic anhydrase (CA) were examined histochemically. If the cells were already damaged before incubation in medium (9 cases), they did not recover in culture. Best results were obtained after 3 to 5 days of culture with a survival rate of more than 90% after 3 days and more than 70% after 5 days, respectively. Both the nonpigmented (NPE) and the pigmented epithelium (PE) of the pars plicata in culture retained the morphological characteristics of epithelia involved in active secretion, namely elaborate infoldings of the cell membranes, numerous mitochondria in the cytoplasm and high activity of Na/K-ATPase and CA. In addition the adjacent capillaries were still fenestrated. After longer incubation times (7-14 days) the NPE and PE cells were filled with increasing amounts of lipid droplets and glycogen granules, indicating changes in metabolism.

Bicarbonate transport mechanisms in rabbit ciliary body epithelium

Sections of whole ciliary body dissected from Dutch belted rabbits were incubated with the cell entrappable pH probe BCECEF-AM. This led to a highly specific localization of epifluorescence emission at the exposed, non-pigmented cell layer (npe) of the dual layered epithelium that covers this organ. The BCECF-loaded tissue sections were superfused in a flow-through chamber and the intracellular pH (pHi) of small groups (10-20) of cells was derived from the ratio of the emission intensities derived from excitations at 490 and 440 nm. In CO2/HCO3- Ringer's, npe pHi = 7.09 +/- 0.11. Replacement of CO2/HCO3- by Hepes increased pHi by 0.22 +/- 0.02, indicating alkali secretory activity under the bicarbonate-rich conditions. Replacement of Cl- by gluconate elicited a rapid, 0.6-U increase in pHi. This effect exhibited little dependence on Na+ and was inhibited by 0.5 mM dihydro-4,4'-diisothiocyanatostilbene -2,2'-disulfonate (H2DIDS). These results indicate the presence of an electroneutral Cl-/base exchange activity. Elevation of [K-] (by partial replacement of Na+) also elicited increases in pHi. In Cl(-)-free media pHi reached 7.8-8.0, a condition under which intracellular [HCO3-] is at least twice as high as its extracellular value. This effect did not occur in the absence of Na+. The Na(+)-dependent high [K+]-induced pHi increase was inhibited by H2DIDS. The effects of Ba2+ on pHi, alone and in combination with high [K+], as well as that of full K+ removal, suggested that the link between high [K+] and pHi increase was mainly due to the effect of cell depolarization on an electronegative Na+ dependent HCO3- transporter. Under normal physiological conditions, the two acid/base transport systems are the main determinants of npe pHi.

Induction of alkoxyresorufin O-dealkylases and UDP-glucuronosyl transferase by phenobarbital and 3-methylcholanthrene in primary cultures of porcine ciliary epithelial cells

Our previous studies have shown that drug-metabolizing activities in the eye are highest in the ciliary body, a tissue responsible for aqueous humor production. In this work, we have separated nonpigmented epithelial (NPE) cells and pigmented epithelial (PE) cells from porcine ciliary body and determined basal and induced activities of 7-ethoxyresorufin (ER) O-dealkylase, 7-pentoxyresorufin (PR) O-dealkylase, and UDP-glucuronosyl transferase (UDP-GT) using primary cultures of separated cells. ER and PR activities were associated primarily with NPE cells and were very low in PE cells. Treatment of NPE cells with phenobarbital (PB) for 48 hr resulted in about a 4-fold increase in PR O-dealkylase activity but only a 1.3-fold rise in ER O-dealkylase activity. Conversely, 3-methylcholanthrene (MC) treatment augmented the ER O-dealkylase activity of NPE cells 6 times over the basal activity in 48 hr but had little effect on PR O-dealkylase activity. Both NPE and PE cells had low basal UDP-GT activities. UDP-GT activity increased about 5-fold in PB-treated PE cells and about 4-fold in PB-treated NPE cells in 48 hr. The results of MC treatment were similar to those of PB treatment; enhancement of UDP-GT was more pronounced in PE cells than in NPE cells. Induction by PB and MC of ER O-dealkylase, PR O-dealkylase and UDP-GT activities in ciliary NPE and PE cells was inhibited almost completely by 3.5 microM cyclohexamide and 40 nM actinomycin D. The heterogeneous distribution of these enzymes suggests that a harmonious interplay between NPE and PE cells is important for metabolic detoxification of blood plasma prior to aqueous humor formation.

Mechanically stripped pigmented and non-pigmented epithelium of the shark ciliary body: morphology and transepithelial electrical properties

Sections of intact ciliary epithelium and mechanically stripped non-pigmented (NPE) and pigmented (PE) cell layers of adult sharks (Squalus acanthias) were mounted in Ussing-type chambers (area 0.1 cm2). Addition of 10(-5) M forskolin to the aqueous side of intact epithelium significantly increased short-circuit current (Isc) within 15 min and a maximum of approx. 30 microA cm-2 was reached after 45-60 min. Transepithelial potential difference (V) increased from -0.8 mV (aqueous side negative as compared with blood/stromal side) to -1.5 mV, whereas resistance (R) was unchanged (50 omega cm2). Forskolin was without effect when applied to the blood side. In stripped PE preparations (R 15 omega cm2), 10(-5) M forskolin applied to the apical side induced a qualitatively similar change of Isc and V compared with the intact tissue. The forskolin-induced effects were fully reversed by 10(-4) M bumetanide and were not dependent on pretreatment of the tissue with 10(-3) M BaCl2. In stripped NPE preparations resistance was usually less than 10 omega cm2 and was not stable. This is consistent with the morphologic observation that although tight junctions were still demonstrable in stripped NPE cells, the apical membranes were damaged. In preparations taken for light and electron microscopy the stripped PE layer revealed intact epithelial cells. In particular, the basal thirds of the stripped PE cells were in very close contact with each other. These attachment zones may have the appearance of tight junctions. Thus the PE cells of the shark ciliary epithelium can be successfully isolated for transepithelial transport studies. The adenylate cyclase system is present in PE cells, and transepithelial transport of chloride may be regulated by intracellular cAMP.

Regional differences in the morphology and enzyme distribution of the spiny dogfish (Squalus acanthias) ciliary epithelium

The ciliary epithelium of spiny dogfish eyes has previously been used for studies of epithelial electrolyte transport and the results are found to be comparable to those obtained in mammals. In this study we report the ultrastructure and enzyme histochemistry of the ciliary epithelium of spiny dogfish in comparison with that of mammals. In contrast to the mammals, the lens in spiny dogfish is connected to the anterior and middle part of the ciliary epithelium by a broad zonula-like suspensory ligament and by a short ligament to the ventral papilla, while the posterior region is mainly free of zonula-like fibers. The non-pigmented epithelium (NPE) of the posterior region shows numerous membrane infoldings, interdigitations and many mitochondria in the cytoplasm as well as histochemical staining for Na+ K(+)-ATPase and carbonic anhydrase (CA). These findings are similar to those seen in the anterior pars plicata of mammals which is mainly involved in aqueous secretion. In the anterior and middle part, the NPE cells have only a few membrane infoldings and few mitochondria in the cytoplasm, but abundant surfaces of rough endoplasmic reticulum, numerous ribosomes and Golgi material, indicating protein synthesis. Histochemically the cells stain for Na+, K(+)-ATPase but not for CA. These findings are comparable to the pars plana in mammals. In contrast to mammals, where the pigmented epithelium (PE) shows nearly no staining for Na+, K(+)-ATPase but an intensive one for CA, the PE cells of spiny dogfish are heavily stained for Na+, K(+)-ATPase in all regions of the eye, but show nearly no staining for CA.

Histochemical demonstration of carbonic anhydrase and Na+/K+-ATPase in the pecten oculi of the fowl

The distribution of carbonic anhydrase (CA) and Na+/K+-ATPase was studied histochemically in the pecten of the fowl by light and electron microscopy. No Na+/K+-ATPase activity was seen by the method used here. CA staining was seen in the membranes of the apical and basal microvilli of the endothelial cells, while the cytoplasm took no stain. There were no staining differences between the capillaries of the different regions of the pecten. Only the capillaries of the bridge showed no microvilli and no staining. Neither did arterioles and venules which lacked microvilli stain. The functional significance of the association of CA activity and microvilli is not clear.