The effect of culture density and proliferation rate on the expression of ouabain-sensitive Na/K ATPase pumps in cultured human retinal pigment epithelium

The nanomechanical role of melanin granules in the retinal pigment epithelium

Nanomechanical properties of cells and tissues, in particular their elasticity, play an important role in different physiological and pathological processes. Recently, we have demonstrated that melanin granules dramatically modify nanomechanical properties of melanoma cells making them very stiff and, as a result, less aggressive. Although the mechanical effect of melanin granules was demonstrated in pathological cells, it was never studied in the case of normal cells. In this work, we analyzed the impact of melanin granules on nanomechanical properties of primary retinal pigment epithelium tissue fragments isolated from porcine eyes. The obtained results clearly show that melanin granules are responsible for the exceptional nanomechanical properties of the tissue. Our findings suggest that melanin granules in the retinal pigment epithelium may play an important role in sustaining the stiffness of this single cell layer, which functions as a natural mechanical barrier separating the retina from the choroid.

Sublethal photic stress and the motility of RPE phagosomes and melanosomes

PURPOSE

To determine whether sublethal oxidative stress to the retinal pigment epithelium by visible light treatment affects the translocation of organelles, notably phagosomes and melanosomes.

METHODS

Isolated porcine melanosomes were phagocytized by ARPE-19 cells, then cultures were treated with blue light to generate reactive oxygen intermediates (ROIs) by endogenous retinal pigment epithelial (RPE) chromophores throughout the cytoplasm. Other melanosomes were preloaded with a photosensitizer before phagocytosis, and cells were light treated to generate ROIs specifically at the granule surface. Phagosome movement was analyzed by live cell imaging. Also analyzed were phagocytized black latex beads, phagocytized melanosomes pretreated to simulate age-related melanin photobleaching, and endogenous RPE melanosomes in primary cultures of porcine retinal pigment epithelium.

RESULTS

Sublethal blue light treatment slowed the movement of some, but not all, phagocytized melanosomes. All phagosomes slowed when ROIs were generated near the organelles through a photosensitized reaction. Melanosome photobleaching, which makes granules more photoreactive, increased the effects of blue light. Blue light treatment also slowed the motility of phagosomes containing latex beads and endogenous pigment granules.

CONCLUSIONS

Blue light-induced stress impairs phagosome motility in RPE cells but affects individual organelles differently, suggesting that the effects of mild oxidative injury vary with subcellular location. The mechanisms underlying slowed motility are at least partially local because slowing can be induced by a photosensitized reaction in the subdomain of the organelle and the magnitude of the slowing is greater when the phagosome contents are photoreactive. Photic stress may impair the movement and positioning of RPE organelles, which would have widespread consequences for maintaining a functionally efficient subcellular organization.

Angiotensin II AT1 receptor stimulates Na+ -K+ATPase activity through a pathway involving PKC-zeta in rat thyroid cells

Angiotensin II (Ang II) receptor subtype 1, AT1, is expressed by the rat thyroid. A relationship between thyroid function and several components of the renin-angiotensin system has also been established, but the Ang II cellular effects in thyrocytes and its transduction signalling remain undefined. The aim of the present paper was to investigate the modulation of the activity of the Na(+)-K(+)ATPase by Ang II and its intracellular transduction pathway in PC-Cl3 cells, an established epithelial cell line derived from rat thyroid. Here we have demonstrated, by RT-PCR analysis, the expression of mRNA for the Ang II AT1 receptor in PC-Cl3 cells; mRNA for the Ang II AT2 receptor was not detected. Ang II was not able to affect the intracellular Ca(2+) concentration in fura-2-loaded cells, but it stimulated the translocation from the cytosol to the plasma membrane of atypical protein kinase C-zeta (PKC-zeta) and -iota (PKC-) isoforms with subsequent phosphorylation of the extracellular signal-regulated kinases 1 and 2 (ERK1 and 2). Translocated atypical PKCs displayed temporally different activations, the activation of PKC-zeta being the fastest. PC-Cl3 cells stimulated with increasing Ang II concentrations showed dose- and time-dependent activation of the Na(+)-K(+)ATPase activity, which paralleled the PKC-zeta translocation time course. Na(+)-K(+)ATPase activity modulation was dependent on PKC activation since the PKC antagonist staurosporine abolished the stimulatory effect of Ang II. The inhibition of the ERK kinases 1 and 2 (MEK1 and 2) by PD098059 (2'-amino-3'-methoxyflavone) failed to block the effect of Ang II on the Na(+)-K(+)ATPase activity. In conclusion, our results suggest that Ang II modulates Na(+)-K(+)ATPase activity in PC-Cl3 cells through the AT1 receptor via activation of atypical PKC-zeta while the Ang II-activated PKC- appears to have other as yet unknown functions.

Activity and expression of Na(+)-K(+)-ATPase in human placental cytotrophoblast cells in culture

1. To determine whether there is a change during differentiation, the activity and expression of Na(+)-K(+)-ATPase were studied in mononucleate cytotrophoblast cells (18 h culture) and syncytiotrophoblast-like cells (66 h culture). A choriocarcinoma-derived cell line (JAr) which, unlike the cytotrophoblast cells, divides in culture, was also studied for comparison. 2. Na(+)-K(+)-ATPase activity was assessed by measurement of ouabain-sensitive 86Rb+ uptake. Na(+)-K(+)-ATPase expression was determined by (i) measurement of [3H]ouabain binding and (ii) Northern hybridization to measure expression of alpha-1 and beta 1-subunit mRNA. 3. There was no significant difference in either activity or expression of Na(+)-K(+)-ATPase during differentiation of cytotrophoblast cells. However, expression of alpha 1- and beta 1-subunit mRNA was significantly lower in 66 vs. 18 h cultured cytotrophoblast cells. 4. Both Na(+)-K(+)-ATPase activity and [3H]ouabain binding was significantly greater in JAr cells than either cytotrophoblast cell groups, although expression of alpha 1- and beta 1-subunit mRNA was the same as cytotrophoblast cells cultured for 18 h. 5. It is concluded that N(+)-K(+)-ATPase activity and protein expression does not change during differentiation of cytotrophoblast cells but that there are changes in expression at the transcriptional or post-transcriptional level.

The short-term increase in extracellular potassium concentration causes DNA replication onset in density-inhibited cells

The high potassium concentration effect on the human diploid fibroblasts (HDF) and 3T3 cells was investigated. The incubation of confluent cultures of HDF or 3T3 Swiss cells in the medium with 50 mM K+ for 35 min induced, 12 h later, the onset of DNA replication in a significant proportion of culture cell population. The same treatment had no effect upon the sparce cell cultures. No stimulation of DNA replication was observed in the absence of serum in culture medium.

Modulation of potassium transport in cultured retinal pigment epithelium and retinal glial cells by serum and epidermal growth factor

The ionic environment of retinal photoreceptors is partially controlled by potassium transporters on retinal glial and retinal pigment epithelial cells (RPE). In this study, serum and epidermal growth factor (EGF) were examined as modulators of potassium transport in confluent cultures of human RPE and rabbit retinal glia. EGF is a known mitogen for confluent RPE cultures and was shown here to also stimulate [3H]thymidine incorporation in cultures of retinal glia. For potassium transport studies 86Rb was used as a tracer during a 17-min incubation. For both retinal cell types the mean total 86Rb uptake in 10% serum was approximately 60% above basal, serum-free controls. For EGF, tested in several experiments in a concentration range from 1 to 100 ng/ml, maximal total uptake was 33 and 24% above controls for RPE and glia, respectively. Inhibitor studies suggested that basal and serum-stimulated uptake for both cell types occurred by the ouabain-sensitive Na-K ATPase pump and by the furosemide- or bumetanide-sensitive Na-K-Cl cotransporter. EGF-stimulated uptake appeared to be due predominantly to the cotransporter. The data suggest that serum components and EGF, which may be available to retina-derived cells under pathologic conditions, may not only stimulate proliferation but may also act as short-term modulators of potassium ion movement and thus affect physiologic processes that are sensitive to ion homeostasis.