(Na+ + K+)-ATPase in C6 glioma and rat cerebrum

Müller cell survival and proliferation in response to medium conditioned by the retinal pigment epithelium

Müller cells have been implicated in the pathogenesis of proliferative vitreoretinopathy and subretinal scar formation; however, the source(s) and signal(s) responsible for their activation are unknown. This study was undertaken to determine if the retinal pigment epithelium (RPE) could be involved in this signaling process by studying its effects on Müller cell survival and division in vitro. A pure population of Müller cells isolated from 1-2 day Long-Evans rats was seeded at low density and treated with medium conditioned by neonatal rat RPE (RPE-CM) or a nonconditioned, defined medium. By day 3, Müller cells cultured in RPE-CM increased in number 2-fold. These cells survived up to 21 days, which was the longest time tested. In contrast, cell number decreased in control wells 75% by day 3, and 100% by day 4. The RPE-mediated survival and proliferation of the Müller cells occurred in a dose-dependent manner. The mitogenic response was specific for the RPE when compared with fibroblasts and non-retinal epithelial cells. Heat and trypsin treatment of the RPE-CM completely abolished its survival and mitogenic activity. These findings demonstrate the establishment of an in vitro model which can be used to investigate RPE-Müller cell interactions. This study also provides evidence for RPE involvement in Müller cell interactions. This study also provides evidence for RPE involvement in Müller cell survival and proliferation.

Muller cell expression of glial fibrillary acidic protein (GFAP) in RPE-cell transplanted retinas of RCS dystrophic rats

In Royal College of Surgeons (RCS) rats with inherited retinal dystrophy, photoreceptor cell degeneration is accompanied by Muller cell changes, in particular, increased expression of the intermediate filament protein, glial fibrillary acidic protein (GFAP). In this study, we examined the expression of GFAP in retinas of 4 month-old RCS dystrophic rats either transplanted with normal retinal pigment epithelial (RPE) cells or injected with vehicle (sham control). The sham-injected and non-treated retinas showed increased expression of GFAP in Muller cells with advancing age. GFAP-immunostained Muller processes were observed in the region of the subretinal space of these RCS retinas beginning by 4 months. However, in the retinas of RCS rats transplanted with normal RPE cells, GFAP expression by Muller cells was significantly reduced. Specifically, under the transplanted RPE cells, GFAP-immunolabeled Muller radial processes were not observed and GFAP immunostaining was not present in the subretinal space at any time period examined. Immunoblot analysis of the superior hemisphere of RPE-cell transplanted retinas of 4 month-old RCS dystrophic rats showed less GFAP immunostaining than sham-injected and the inferior hemisphere of retinas of age-matched RCS rats. This study showed that in normal RPE-cell transplanted retinas of RCS rats, in addition to rescued photoreceptor cells, there was an accompanying stabilization of Muller cells as demonstrated by a reduction in the expression of GFAP.

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.

(Na+ + K+)-ATPase and opsin in retinas of RCS dystrophic rats: time course study

Retinas of Royal College of Surgeons (RCS) dystrophic rats were investigated immunocytochemically for the distribution of the membrane-bound enzyme (Na+ + K+)-ATPase and the photo-pigment opsin prior to and during the retinal disease process. Retinas of 11 day-old dystrophic and control Long Evans rats showed (Na+ + K+)-ATPase immunostain most dense in the outer nuclear layer (ONL) and inner plexiform layer (IPL). Also, in these retinas, immunostaining for opsin was dense along rod inner segments (RIS) and on plasmalemma of ONL cell bodies and several cell bodies in the inner nuclear layer (INL). In retinas of control rats at 30 days and later, less dense (Na+ + K+)-ATPase immunostain was detected in the ONL than at 11 days and opsin-immunostained ROS were also detected. However, (Na+ + K+)-ATPase immunostained RIS were shorter in retinas of 30 day-old dystrophic than in retinas of age-matched control rats and an opsin-immunostained debris zone was also observed in dystrophic retinas. In retinas of 60 day-old dystrophic rats, the opsin-immunostained debris zone was more prominent than at 30 days, while the few ONL cell bodies immunostained for both proteins. Also, the outer IPL of 60 day-old dystrophic rat retinas immunostained more densely for (Na+ + K+)-ATPase than the inner IPL. In 120 day-old dystrophic rat retinas, (Na+ + K+)-ATPase immunostain was detected in the INL and IPL, while opsin staining was demonstrated only in the debris zone. This opsin-immunostained debris disappeared in a central-to-peripheral gradient. (Na+ + K+)-ATPase immunostain was still present in the INL and IPL in retinas and the optic nerve of one year-old RCS dystrophic rats; however, opsin was restricted to a few surviving cell bodies in the peripheral retina.

Functional and structural characteristics of photoreceptor cells rescued in RPE-cell grafted retinas of RCS dystrophic rats

In this study retinas of pink-eyed 26 day-old RCS dystrophic rats were injected with normal, melanotic retinal pigment epithelial (RPE) cells into the subretinal space. The areas containing underlying photoreceptor cells were subsequently investigated by electron microscopy at 60 days and light microscopy immunocytochemistry at 60 and 120 days. Retinal regions containing viable RPE-cell grafts exhibited melanin-contained RPE cell transplants attached to Bruch's membrane and containing shed rod outer segments (ROS). Also, the ROS of these photoreceptor cells exhibited a normal-appearing structural relationship with apical membrane projections of these RPE cells. The debris zone, prominent in retinas of 60 day-old RCS dystrophic rats, was much reduced in RPE-cell grafted regions. By at least 3 months after RPE transplantation, immunostaining for Na+,K+-ATPase was demonstrated along inner segments (IS) of photoreceptor cells in grafted regions, as was also shown in control retinas, but not in non-grafted regions. Opsin immunostaining in RPE-cell grafted regions and in control retinas was detected along ROS and rod inner segments (RIS) and at the periphery of cell bodies in the outer nuclear layer. This study has shown that transplanted normal RPE cells in retinas of RCS dystrophic rats appear to have normal functional and structural characteristics at least three months after transplantation. Furthermore, the rescued PRC's exhibited a normal distribution of and immunostaining density for the membrane-bound enzyme Na+,K+-ATPase and the photo-pigment opsin.

Na+, K+-ATPase activity in cultured C6 glioma cells

Rat C6 glioma cells were cultured for 4 days in MEM medium supplemented with 10% bovine serum and Na+, K+-ATPase activity was determined in homogenates of harvested cells. Approximately 50% of enzyme activity was attained at 1.5 mM K+ and the maximum (2.76 +/- 0.13 mumol Pi/h/mg protein) at 5 mM K+. The specific activity of Na+, K+-ATPase was not influenced by freezing the homogenates or cell suspensions before the enzyme assay. Ten minutes' exposure of glioma cells to 10(-4) or 10(-5) M noradrenaline (NA) remained without any effect on NA+, K+-ATPase activity. Neither did the presence of NA in the incubation medium, during the enzyme assay, influence the enzyme activity. The nonresponsiveness of Na+, K+-ATPase of C6 glioma cells to NA is consistent with the assumption that alpha (+) form of the enzyme may be preferentially sensitive to noradrenaline. Na+, K+-ATPase was inhibited in a dose-dependent manner by vanadate and 50% inhibition was achieved at 2 x 10(-7) M concentration. In spite of the fact that Na+, K+-ATPase of glioma cells was not responsive to NA, the latter could at least partially reverse vanadate-induced inhibition of the enzyme. Although the present results concern transformed glial cells, they suggest the possibility that inhibition of glial Na+, K+-ATPase may contribute to the previously reported inhibition by vanadate of Na+, K+-ATPase of the whole brain tissue.

Immunocytochemical localization of (Na+ + K+)-ATPase in the rat hippocampus

The adult rat hippocampus was investigated by light microscopic immunocytochemistry for (Na+ + K+)-ATPase. In the CA1, CA2 and CA3 hippocampal regions, dense immunostaining for (Na+ + K+)-ATPase, exhibiting a punctate appearance, was demonstrated along the soma plasmalemma of hippocampal pyramidal cells in the stratum pyramidale, thus outlining these cells distinctly, and along dendrites extending into the stratum radiatum. (Na+ + K+)-ATPase immunostaining was dense in the neuropil of the strata oriens and radiatum of the rat hippocampus, but much lighter in the corpus callosum. Immunostaining at the periphery of pyramidal cell soma may be associated with the plexus formed by axon terminals of hippocampal basket cells.