Mucosal-associated invariant T-cell tumor infiltration predicts long-term survival in cholangiocarcinoma

BACKGROUND AND AIMS

Cholangiocarcinoma (CCA) is a malignancy arising from biliary epithelial cells of intra- and extrahepatic bile ducts with dismal prognosis and few nonsurgical treatments available. Despite recent success in the immunotherapy-based treatment of many tumor types, this has not been successfully translated to CCA. Mucosal-associated invariant T (MAIT) cells are cytotoxic innate-like T cells highly enriched in the human liver, where they are located in close proximity to the biliary epithelium. Here, we aimed to comprehensively characterize MAIT cells in intrahepatic (iCCA) and perihilar CCA (pCCA).

APPROACH AND RESULTS

Liver tissue from patients with CCA was used to study immune cells, including MAIT cells, in tumor-affected and surrounding tissue by immunohistochemistry, RNA-sequencing, and multicolor flow cytometry. The iCCA and pCCA tumor microenvironment was characterized by the presence of both cytotoxic T cells and high numbers of regulatory T cells. In contrast, MAIT cells were heterogenously lost from tumors compared to the surrounding liver tissue. This loss possibly occurred in response to increased bacterial burden within tumors. The residual intratumoral MAIT cell population exhibited phenotypic and transcriptomic alterations, but a preserved receptor repertoire for interaction with tumor cells. Finally, the high presence of MAIT cells in livers of iCCA patients predicted long-term survival in two independent cohorts and was associated with a favorable antitumor immune signature.

CONCLUSIONS

MAIT cell tumor infiltration associates with favorable immunological fitness and predicts survival in CCA.

A biliary immune landscape map of primary sclerosing cholangitis reveals a dominant network of neutrophils and tissue-resident T cells

The human biliary system, a mucosal barrier tissue connecting the liver and intestine, is an organ often affected by serious inflammatory and malignant diseases. Although these diseases are linked to immunological processes, the biliary system represents an unexplored immunological niche. By combining endoscopy-guided sampling of the biliary tree with a high-dimensional analysis approach, comprehensive mapping of the human biliary immunological landscape in patients with primary sclerosing cholangitis (PSC), a severe biliary inflammatory disease, was conducted. Major differences in immune cell composition in bile ducts compared to blood were revealed. Furthermore, biliary inflammation in patients with PSC was characterized by high presence of neutrophils and T cells as compared to control individuals without PSC. The biliary T cells displayed a CD103⁺CD69⁺ effector memory phenotype, a combined gut and liver homing profile, and produced interleukin-17 (IL-17) and IL-22. Biliary neutrophil infiltration in PSC associated with CXCL8, possibly produced by resident T cells, and CXCL16 was linked to the enrichment of T cells. This study uncovers the immunological niche of human bile ducts, defines a local immune network between neutrophils and biliary-resident T cells in PSC, and provides a resource for future studies of the immune responses in biliary disorders.

Chronic hepatitis delta virus infection leads to functional impairment and severe loss of MAIT cells

BACKGROUND & AIMS

Hepatitis delta virus (HDV) infection is the most severe form of viral hepatitis. Although HDV-associated liver disease is considered immune-mediated, adaptive immune responses against HDV are weak. Thus, the role of several other cell-mediated mechanisms such as those driven by mucosa-associated invariant T (MAIT) cells, a group of innate-like T cells highly enriched in the human liver, has not been extensively studied in clinical HDV infection.

METHODS

MAIT cells from a sizeable cohort of patients with chronic HDV were analyzed ex vivo and in vitro after stimulation. Results were compared with MAIT cells from hepatitis B virus (HBV) monoinfected patients and healthy controls.

RESULTS

Circulating MAIT cells were dramatically decreased in the peripheral blood of HDV-infected patients. Signs of decline were also observed in the liver. In contrast, only a modest decrease of circulating MAIT cells was noted in HBV monoinfection. Unsupervised high-dimensional analysis of residual circulating MAIT cells in chronic HDV infection revealed the appearance of a compound phenotype of CD38^hiPD-1^hiCD28^loCD127^loPLZF^loEomes^loHelios^lo cells indicative of activation. Corroborating these results, MAIT cells exhibited a functionally impaired responsiveness. In parallel to MAIT cell loss, HDV-infected patients exhibited signs of monocyte activation and increased levels of proinflammatory cytokines IL-12 and IL-18. In vitro, IL-12 and IL-18 induced an activated MAIT cell phenotype similar to the one observed ex vivo in HDV-infected patients. These cytokines also promoted MAIT cell death, suggesting that they may contribute to MAIT cell activation and subsequent loss during HDV infection.

CONCLUSIONS

These results suggest that chronic HDV infection engages the MAIT cell compartment causing activation, functional impairment, and subsequent progressive loss of MAIT cells as the HDV-associated liver disease progresses.

LAY SUMMARY

Hepatitis delta virus (HDV) infection is the most severe form of viral hepatitis. We found that in patients with HDV, a subset of innate-like T cells called mucosa-associated invariant T cells (or MAIT cells), which are normally abundant in peripheral blood and the liver, are activated, functionally impaired and severely depleted.

Confidence Interval Constraint-Based Regularization Framework for PET Quantization

In this paper, a new generic regularized reconstruction framework based on confidence interval constraints for tomographic reconstruction is presented. As opposed to usual state-of-the-art regularization methods that try to minimize a cost function expressed as the sum of a data-fitting term and a regularization term weighted by a scalar parameter, the proposed algorithm is a two-step process. The first step concentrates on finding a set of images that rely on the direct estimation of confidence intervals for each reconstructed value. Then, the second step uses confidence intervals as a constraint to choose the most appropriate candidate according to a regularization criterion. Two different constraints are proposed in this paper. The first one has the main advantage of strictly ensuring that the regularized solution will respect the interval-valued data-fitting constraint, thus preventing over-smoothing of the solution while offering interesting properties in terms of spatial and statistical bias/variance trade-off. Another regularization proposition based on the design of a smoother constraint also with appealing properties is proposed as an alternative. The competitiveness of the proposed framework is illustrated in comparison to other regularization schemes using analytical and GATE-based simulation and real PET acquisition.

Hepatitis C virus-induced natural killer cell proliferation involves monocyte-derived cells and the OX40/OX40L axis

BACKGROUND & AIMS

Natural killer (NK) cells are found at increased frequencies in patients with hepatitis C virus (HCV). NK cell activation has been shown to correlate with HCV clearance and to predict a favourable treatment response. The aim of our study was to dissect mechanisms leading to NK cell activation and proliferation in response to HCV.

METHODS

NK cell phenotype, proliferation, and function were assessed after the 6-day co-culture of human peripheral blood mononuclear cells with either HCV replicon-containing HuH6 hepatoblastoma cells or HCV-infected HuH7.5 cells. The results obtained were confirmed by immunohistochemistry of liver biopsies from patients with HCV and from HCV-negative controls.

RESULTS

In HCV-containing co-cultures, a higher frequency of NK cells upregulated the expression of the high-affinity IL-2 receptor chain CD25, proliferated more rapidly, and produced higher amounts of interferon γ compared with NK cells from control co-cultures. This NK cell activation was dependent on IL-2, cell-cell contact-mediated signals, and HCV replicon-exposed monocytes. The tumour necrosis factor-receptor superfamily member OX40 was induced on the activated CD25^± NK cell subset and this induction was abrogated by the depletion of CD14⁺ monocytes. Moreover, OX40L was upregulated on CD14^± monocyte-derived cells co-cultured with HCV-containing cells and also observed in liver biopsies from patients with HCV. Importantly, blocking of the OX40/OX40L interaction abolished both NK cell activation and proliferation.

CONCLUSIONS

Our results uncover a previously unappreciated cell-cell contact-mediated mechanism of NK cell activation and proliferation in response to HCV, mediated by monocyte-derived cells and the OX40/OX40L axis. These results reveal a novel mode of crosstalk between innate immune cells during viral infection.

LAY SUMMARY

Using a cell-culture model of hepatitis C virus (HCV) infection, our study revealed that natural killer (NK) cells become activated and proliferate when they are co-cultured with HCV-containing liver cells. The mechanism of this activation involves crosstalk with other innate immune cells and a cell-cell contact interaction mediated by the cell surface molecules OX40 and OX40L. Our study reveals a novel pathway leading to NK cell proliferation and activation against virus-infected cells that might be of relevance in antiviral immunity.

Immunofluorescence identifies distinct subsets of endothelial cells in the human liver

As well as systemic vascular endothelial cells, the liver has specialised sinusoidal endothelial cells (LSEC). LSEC dysfunction has been documented in many diseased states yet their phenotype in normal human liver has not been comprehensively assessed. Our aim was to improve characterisation of subsets of endothelial cells and associated pericytes in the human liver. Immunofluorescence microscopy was performed on normal human liver tissue samples to assess endothelial and structural proteins in a minimum of three donors. LSEC are distributed in an acinar pattern and universally express CD36, but two distinctive subsets of LSEC can be identified in different acinar zones. Type 1 LSEC are CD36^hiCD32⁻CD14⁻LYVE-1⁻ and are located in acinar zone 1 of the lobule, while Type 2 LSEC are LYVE-1⁺CD32^hiCD14⁺CD54⁺CD36^mid-lo and are located in acinar zones 2 and 3 of the lobule. Portal tracts and central veins can be identified using markers for systemic vascular endothelia and pericytes, none of which are expressed by LSEC. In areas of low hydrostatic pressure LSEC are lined by stellate cells that express the pericyte marker CD146. Our findings identify distinctive populations of LSEC and distinguish these cells from adjacent stellate cells, systemic vasculature and pericytes in different zones of the liver acinus.

[About the Effects of VEGF-A Antagonists on Molecular and Cellular Level]

Anti-VEGF-A therapy is successfully established as a routine therapy to treat wet age-related macular degeneration. Indications have been extended to other retinal diseases. Three different substances have been demonstrated to be active. However, the efficacy of these substances is highly variable in heterogeneous groups of patients and may include non-responders and relapses, so that there may be very individual treatment effects. It is speculated that differences in the molecular properties or structures of the three substances might explain these observations. This article therefore summarises the recent publications on this topic and discusses their relevance. Apart from common features such as VEGF-A affinity, the substances exhibit differences, including the stability of the VEGF-A/molecule complexes and the ability to neutralise angiogenic molecules other than only VEGF-A. At the cellular level, a variety of different methods have been used and the results are often inconsistent. It is therefore not yet possible to predict the clinical properties of VEGF-A neutralising substances on the basis of their known molecular properties or cellular effects.

Acute obturator internus muscle strain in a rugby player: a case report

A 28-year-old male rugby player presented with severe onset of right hip pain when he fell awkward after a ruck during an international match. A rare case of an acute strain of the obturator internus muscle, a deep muscle of the hip joint, is reported, which resolved completely after a period of rest and intense active physical therapy.

The immunophenotype of antigen presenting cells of the mononuclear phagocyte system in normal human liver--a systematic review

The mononuclear phagocytic system (MPS), comprised of monocytes, macrophages, and dendritic cells, is essential in tissue homeostasis and in determining the balance of the immune response through its role in antigen presentation. It has been identified as a therapeutic target in infectious disease, cancer, autoimmune disease and transplant rejection. Here, we review the current understanding of the immunophenotype and function of the MPS in normal human liver. Using well-defined selection criteria, a search of MEDLINE and EMBASE databases identified 76 appropriate studies. The majority (n=67) described Kupffer cells (KCs), although the definition of KC differs between sources, and little data were available regarding their function. Only 10 papers looked at liver dendritic cells (DCs), and largely confirmed the presence of the major dendritic cell subsets identified in human blood. Monocytes were thoroughly characterized in four studies that utilized flow cytometry and fluorescent microscopy and highlighted their prominent role in liver homeostasis and displayed subtle differences from circulating monocytes. There was some limited evidence that liver DCs are tolerogenic but neither liver dendritic cell subsets nor macrophages have been thoroughly characterized, using either multi-colour flow cytometry or multi-parameter fluorescence microscopy. The lobular distribution of different subsets of liver MPS cells was also poorly described, and the ability to distinguish between passenger leukocytes and tissue resident cells remains limited. It was apparent that further research, using modern immunological techniques, is now required to accurately characterize the cells of the MPS in human liver.

Ocular delivery systems for poorly soluble drugs: an in-vivo evaluation

For highly potent but poorly water-soluble drugs like cyclosporine A, the development of aqueous formulations providing an increase of corneal drug tissue levels, and thus of bioavailability, to increase patient compliance is still a challenge. Therefore, we designed two water-based liquid application systems, an in-situ nanosuspension (INS) and a micellar solution (MS), and tested both formulations in vivo at the rabbit cornea for tolerability and the tissue uptake of CsA. The evaluation of the biological tolerability by periodical eye examination during 180 min and quantification in a defined grading system revealed that the INS evoked minimal to no irritations whereas the MS was perfectly tolerated. After the observation period, the rabbits were sacrificed and the corneal tissue levels of CsA were analyzed. The INS and the MS both showed high levels of 1683±430 ngCsA/gcornea and 826±163 ngCsA/gcornea, respectively, and exceeded drug tissue levels reported for Restasis(®) (350 ngCsA/gcornea) and cationic emulsions (750 ngCsA/gcornea). These results marked our INS and MS as outstanding novel approaches for the treatment of inflammatory corneal diseases.

[An analysis of the pathophysiology of inherited diseases]

Evidence-based ophthalmology relies on a knowledge of the pathophysiological mechanisms at the molecular level. An example is the anti-VEGF therapy to treat the wet form of age-related macular degeneration. Its therapeutic effect is due to the neutralisation of a single type of molecule, the VEGF-A. The analysis of pathophysiological mechanisms of inherited diseases represents a unique opportunity to develop precise molecular therapeutic approaches. This analysis begins with the identification of the responsible gene which is followed by investigation of the function of its gene product along with the mutation-dependent changes using animal models and investigation of single molecules in expression systems. In this process the investigation of the pathomechanisms plays a central role. This review provides an orientation about studies on the pathophysiology of inherited diseases with a description of its methods and basic pathomechanisms. Furthermore, examples will be given on how the analysis of inherited retinal diseases has led to an understanding of the pathomechanisms of acquired diseases such as age-dependent macular degeneration and to the development of new therapeutic approaches.

[Function of bestrophin]

Clarification of the function of bestrophin, the gene product of VMD2, establishes a basis for the understanding of the pathomechanisms leading to Best's vitelliform macular degeneration. Studies of heterologously expressed bestrophin showed that bestrophin can function as a Cl(-) channel. All four known bestrophins were found to display Cl(-) channel activity. A loss in Cl(-) channel function would elegantly explain the development of the leading symptom for Best's disease, the reduction of the light peak amplitude in the patient's electro-oculogram. However, there are still gaps in the chain of evidence demonstrating that bestrophin is a Cl(-) channel, and this hypothesis is inconsistent with newly published follow-up observations. In an alternative hypothesis bestrophin appears as a regulator of voltage-dependent Ca(2+) channels assuming an indirect involvement of bestrophin in the generation of the light peak. Further studies on either bestrophin-deficient mice or transgenic mice will show that either one of the hypotheses is right or maybe both will be proven correct, showing bestrophin as a Cl(-) channel and Ca(2+) channel regulator.

Flufenamic acid enhances current through maxi-K channels in the trabecular meshwork of the eye

PURPOSE

Flufenamic acid relaxes trabecular meshwork, a smooth muscle-like tissue involved in the regulation of ocular outflow in the eye. In this study, we attempted to determine if ionic channels are involved in this response.

METHODS

Cultured human (HTM) and bovine (BTM) trabecular meshwork cells were investigated using the patch-clamp technique.

RESULTS

In trabecular meshwork, flufenamic acid (10(-5) M) reversibly stimulated outward current to 406 +/- 71% of initial outward current level in BTM (n = 10) and 294 +/- 75% of initial current level in HTM (n = 12) in all cells investigated; no significant differences emerged. The response was dosage-dependent. Replacement of potassium in all solutions eliminated the response to flufenamic acid (n = 4, BTM). Blocking K(ATP ) channels with glibenclamide (10(-5) M, n = 6) and small-conductance calcium-activated potassium channels with apamin (10(-6) M, n = 5) had no effect. A direct effect on calcium channels could also not be detected. Blockage of the large-conductance calcium-activated potassium channel (maxi-K) by iberiotoxin (10(-7) M) suppressed 87 +/- 9% (n = 6; HTM) and 91 +/- 10% (n = 6; BTM) of the response. Depleting the cells of calcium did not significantly alter the response to flufenamic acid.

CONCLUSIONS

Flufenamic acid stimulates maxi-K channels in trabecular meshwork of both human and bovine origin. This should lead to hyperpolarization, closure of L-type channels and lowered cytosolic calcium levels, possibly explaining the relaxation observed in response to this substance.

Fibroblast growth factor receptor 2 (FGFR2) in brain neurons and retinal pigment epithelial cells act via stimulation of neuroendocrine L-type channels (Ca(v)1.3)

In contrast to the fibroblast growth factor receptor 1 (FGFR1), little is known about intracellular signaling of FGFR2. The signaling cascade of FGFR2 was studied using the perforated patch configuration of the patch-clamp technique in cultured rat retinal pigment epithelial (RPE) cells that express both FGFR1 and FGFR2. Interaction of signaling proteins was studied using immunoprecipitation techniques with membrane proteins from RPE cells and freshly isolated rat brain. When Ba(2+) currents through L-type channels were studied, extracellular application of bFGF (10 ng/ml) led to a shift of the steady-state activation to more negative values. In 50% of cells, an additional increase in maximal current amplitude was observed. This effect was blocked by the tyrosine kinase inhibitor lavendustin A (10(-5) M) but was not influenced by the FGFR1 blocker SU5402 (2 x 10(-5) M) or by the blocker for src-kinase herbimycin A (10(-5) M). Immunoprecipitation of FGFR2 led to coprecipitation of alpha 1D Ca(2+) channel subunits and precipitation of alpha 1D subunits led to coprecipitation of FGFR2. Immunoprecipitation of FGFR1 did not result in the coprecipitation with alpha 1D Ca(2+) channel subunits. The coprecipitation results were comparable when using brain tissue and RPE cells. The alpha 1D subunit-specific band were stained with antiphosphotyrosine antibodies. We conclude that FGFR2 acts via a different signaling cascade than FGFR1. This cascade involves an src-kinase-independent, close functional interaction of FGFR2 and the alpha subunit of neuroendocrine L-type channels.

Muscarinic receptors of the M2 subtype in human and bovine trabecular meshwork

BACKGROUND

The trabecular meshwork is a tissue actively involved in the regulation of intraocular pressure via contractile mechanisms. The present study was performed to investigate the effects of muscarinic m2-receptor antagonists on trabecular meshwork contractility and to identify the m2 muscarinic receptor in human and bovine trabecular meshwork cells.

METHODS

Isometric tension measurements of bovine trabecular meshwork strips were performed using a custom-made force length transducer. Western blot and immunoprecipitation analysis was used to detect the m2-receptor proteins in membrane preparations of human and bovine trabecular meshwork cells.

RESULTS

Immunoblotting results showed the expression of an m2-receptor protein band at 56 kDa in both human and bovine trabecular meshwork cells. Two different m2-receptor antagonists were tested on trabecular meshwork contractility. After carbachol-induced contraction (10(-6) M set to 100% contractile force), specific m2-receptor antagonists were applied. 3 alpha-Chloroimperaline (10(-6) M) had no effect on the maximal carbachol-induced contraction in trabecular meshwork strips. Methoctramine induced a significant relaxation at concentrations of 10(-7), 10(-6) and 5 x 10(-6) M even in the presence of m1- and m3-receptor antagonists.

CONCLUSION

These data indicate that in addition to the m3-receptor subtype present in the trabecular meshwork this tissue also features the m2 receptor. This receptor is partly involved in the regulation of trabecular meshwork contractility, suggesting that outflow facility might be influenced through this receptor.

Mediation of calcium-independent contraction in trabecular meshwork through protein kinase C and rho-A

PURPOSE

Inhibition of protein kinase C (PKC) and rho-kinase (ROCK) may represent a new way of influencing outflow facility through isolated relaxation of the trabecular meshwork (TM). This work was performed to investigate the existence of calcium-independent contraction in this smooth-muscle-like tissue and its modulation by targeting the rho-guanosine triphosphatase (GTPase)-mediated pathway.

METHODS

Isometric tension measurements of bovine TM and ciliary muscle (CM) were performed. Intra- and extracellular calcium buffering was accomplished with EGTA and 1, 2-bis(2-aminophenoxy)-ethane-N,N:,N:,N:',N:'-tetra-acetic acid tetrakis/acetoxymethhyl ester (BAPTA-AM) followed by stimulation of PKC with phorbolester (PMA) or 4alpha-phorbol. Calcium-independent contraction was blocked using the highly specific ROCK inhibitor Y-27632. Western blot analysis and immunoprecipitation was performed using human TM cells.

RESULTS

In TM, carbachol induced partial contraction under conditions of extracellular calcium depletion (22. 1% +/- 2.3% versus 100%, n = 9). The membrane-permeable calcium chelator BAPTA-AM completely blocked this response (1.1% +/- 1.4% versus 100%, n = 9). When calcium was completely blocked, PMA induced contraction in TM (16.7% +/- 5.9% versus 100%, n = 9) but not in CM (1.8% +/- 2.5% versus 100%, n = 6). The inactive PMA analogue 4alpha-phorbol did not induce contraction, indicating that activation of PKC is involved in this contractile response. The ROCK inhibitor Y-27632 completely blocked the calcium-independent PMA-induced contraction in TM. Western blot analysis and immunoprecipitation revealed the expression of the rho-A protein in human TM cells.

CONCLUSIONS

The data indicate that contrary to CM, the TM features calcium-independent contractile mechanisms linked to rho-A and PKC isoforms that do not require calcium for activation. ROCK inhibitors may allow specific modulation of the TM to enhance outflow facility, thus lowering intraocular pressure.

The Royal College of Surgeons rat: an animal model for inherited retinal degeneration with a still unknown genetic defect

The Royal College of Surgeons (RCS) rat is the first known animal with inherited retinal degeneration. Despite the fact that the genetic defect is not known, the RCS rat is widely used for research in hereditary retinal dystrophies. This review tries to summarize observations which have been made in the RCS rat and to make an attempt to formulate candidate genes which may the cause for the retinal degeneration in this rat strain. The genetic defect in RCS rats causes the inability of the retinal pigment epithelium (RPE) to phagocytose shed photoreceptor outer segments. In normal rats or humans, this circadian process is regulated by both the cyclic adenosine monophosphate (cAMP) and the calcium/ inositol phosphate systems. The calcium/inositol phosphate system seems to be linked to the phagocytosis receptors which recognize photoreceptor outer membranes to initialize phagocytosis. The cAMP system appeared as modulator of the regulation of phagocytosis. An increase in the intracellular cAMP concentration is an 'off' signal for phagocytosis. In RPE cells from RCS rats many observations have been made which indicate a changed second messenger metabolism concerning both the cAMP and the calcium/inositol phosphate systems. The genetic defect seems to concern a protein which is involved in the initialization of a second messenger pathway. We conclude that the genes coding for the phagocytosis receptor or for proteins which are linked to receptors (for example G proteins) are good candidates for defective genes in RCS rats.

Activation of neuroendocrine L-type channels (alpha1D subunits) in retinal pigment epithelial cells and brain neurons by pp60(c-src)

The aim of this study is to characterize the subtype of tyrosine kinase-regulated L-type Ca(2+) channels in retinal pigment epithelial (RPE) cells. Ca(2+) channel alpha1D-subunits were enriched by immunoprecipitation from membrane proteins isolated from rat RPE cells. Western blot analysis of the precipitates revealed coprecipitation of pp60(c-src). In addition, in precipitates obtained with antibodies against pp60(c-src), alpha1D-subunits were identified. The same was observed in immunoprecipitations from rat brain neurons. Tyrosine phosphorylation of alpha1D-subunits was confirmed using anti-phosphotyrosine antibodies. Ba(2+) currents through L-type channels in cultured rat RPE cells were increased by intracellular application of active pp60(c-src) (30 U/ml) (heat-inactivated pp60(c-src) had no effect). Thus, L-type channels of the neuroendocrine subtype can be expressed in epithelial cells and are activated by tyrosine kinase of the src subtype. This kind of regulation is also suggested for brain-derived neurons.

Influence of muscarinic agonists and tyrosine kinase inhibitors on L-type Ca(2+)Channels in human and bovine trabecular meshwork cells

Trabecularmeshwork (TM), a smooth muscle-like tissue with contractile properties, is involved in the regulation of aqueous humor outflow. However, little is known about the regulation of Ca(2+)influx in trabecular meshwork cells. We investigated the influence of acetylcholine and tyrosine kinases on Ca(2+)conductances of bovine TM (BTM) and human TM (HTM) cells using the perforated-patch configuration of the patch-clamp technique and measurements of intracellular free Ca(2+)([Ca(2+)](i)). Depolarization of the cells in the presence of 10 m m Ba(2+)or Ca(2+)led to an activation of inward currents at potentials positive to -30 mV with characteristics typical of L-type Ca(2+)currents: when using 10 m m Ba(2+), maximal inward current and inactivation time constant (tau) increased; the L-type Ca(2+)channel blocker nifedipine (1 microm) reduced and the L-type Ca(2+)channel agonist BayK8644 (5 microm) enhanced maximal inward current. Acetylcholine (100 microm) and carbachol (1 microm) led to an increase in inward Ba(2+)current whereas application of the tyrosine kinase inhibitors genistein (50 microm) and lavendustin A (20 microm) resulted in a decrease in inward current. The application of daidzein (10 microm), an inactive analog of genistein had no effect. Depolarization of the cells with 135 m m K(+)or direct stimulation of L-type channels by application of BayK 8644 led to an increase in [Ca(2+)](i). Carbachol (1 microm) induced an increase in [Ca(2+)](i)which was decreased by application of the tyrosine kinase inhibitor genistein (50 microm). We conclude that HTM and BTM cells express voltage-dependent L-type Ca(2+)channels that influence intracellular Ca(2+)concentration and thus may modulate TM contractility. The activity of L-type Ca(2+)currents is influenced by muscarinic agonists and tyrosine kinases.

Physiological features of primary cultures and subcultures of human retinal pigment epithelial cells before and after cryopreservation for cell transplantation

BACKGROUND

One striking disadvantage of in vitro culturing of human retinal pigment epithelial (RPE) cells is the loss of epithelial differentiation and specific cell function during culture. This may be one of the main reasons for the failure of RPE cell transplantation. The aim of this study was to evaluate cell culture conditions ensuring the maintenance of differentiation and function of RPE cells after subcultivation and storage in liquid nitrogen.

METHODS

Enzymatically isolated cells were seeded onto coated culture dishes, cultured with a specially formulated improved growth medium until confluence and then cryopreserved in liquid nitrogen for 16-66 months. HLA class I and II typing was performed before cryopreservation and after thawing. Expression of Ca2+ channels in primary, first-passage and cryopreserved RPE cells was studied using the patch-clamp technique.

RESULTS

After cryopreservation no loss of any HLA antigen was detectable in 12 of 14 cell strains studied. Patch-clamp experiments demonstrated that high-threshold L-type Ca2+ channels, which are typical for freshly isolated cells, could be detected in first-passage and cryopreserved RPE cells only when improved culture conditions were employed, not in conventionally cultured cells. The characteristics of these channels showed little change in subcultured cells compared to primary cultures.

CONCLUSION

This is the first study showing the maintenance of adult human RPE-specific cell differentiation and characteristics in vitro after primary culture and after cryopreservation using improved cell culture methods. The optimization and quality control of cell culture is an important prerequisite for successful cell transplantation.

The effects of protein kinase C on trabecular meshwork and ciliary muscle contractility

PURPOSE

The possible role of protein kinase C (PKC) inhibitors in novel pressure-lowering drugs is currently under investigation. To gain further insight into regulation of contractility by PKC in trabecular meshwork (TM) and ciliary muscle (CM), the effects of various PKC inhibitors and activators were tested.

METHODS

Isometric tension measurements of bovine TM and CM strips were performed. PKC was stimulated by phorbol ester and by the diacylglycerol analogue diC8. PKC blockade was accomplished using H7 and myristoilated PKC substrate (mPKC). Western blot analysis was used to identify specific PKC isoforms in human trabecular meshwork (HTM), human ciliary muscle (HCM), and bovine TM and CM.

RESULTS

In tissues precontracted by carbachol PKC antagonist H7 led to a relaxation of TM (25+/-7.2 versus 100%; n = 8) with no effect on CM. mPKC substrate selectively blocks PKC. This substance led to relaxation of TM (32.8+/-7.4 versus 100%, n = 7), whereas CM was not affected. PMA at concentrations of 10(-6) M led to a slow contraction of both tissues that was more marked in TM. DiC8 and 4alpha-phorbol had no effect on contractility. Western blot analysis revealed expression of calcium-dependent PKC-alpha and calcium-independent PKC-epsilon isoforms in HTM and HCM. PKC-epsilon expression was more pronounced in HTM than in HCM. Similar PKC isoform expression was found in native bovine tissue.

CONCLUSIONS

PKC isoforms show different tissue distributions in human and bovine TM and CM. Contractility differences exist in both tissues in response to PKC antagonists and agonists. The data indicate that PKC may be involved in regulation of aqueous humor outflow by the TM. Thus, inhibition of PKC may represent a new way of influencing outflow facility through isolated relaxation of TM.

Involvement of protein tyrosine kinase in the InsP3-induced activation of Ca2+-dependent Cl- currents in cultured cells of the rat retinal pigment epithelium

This combined study of patch-clamp and intracellular Ca2+ ([Ca2+]i) measurement was undertaken in order to identify signaling pathways that lead to activation of Ca2+-dependent Cl- channels in cultured rat retinal pigment epithelial (RPE) cells. Intracellular application of InsP3 (10 microM) led to an increase in [Ca2+]i and activation of Cl- currents. In contrast, intracellular application of Ca2+ (10 microM) only induced transient activation of Cl- currents. After full activation by InsP3, currents were insensitive to removal of extracellular Ca2+ and to the blocker of ICRAC, La3+ (10 microM), despite the fact that both maneuvers led to a decline in [Ca2+]i. The InsP3-induced rise in Cl- conductance could be prevented either by thapsigargin-induced (1 microM) depletion of intracellular Ca2+ stores or by removal of Ca2+ prior to the experiment. The effect of InsP3 could be mimicked by intracellular application of the Ca2+-chelator BAPTA (10 mm). Block of PKC (chelerythrine, 1 microM) had no effect. Inhibition of Ca2+/calmodulin kinase (KN-63, KN-92; 5 microM) reduced Cl--conductance in 50% of the cells investigated without affecting [Ca2+]i. Inhibition of protein tyrosine kinase (50 microM tyrphostin 51, 5 microM genistein, 5 microM lavendustin) reduced an increase in [Ca2+]i and Cl- conductance. In summary, elevation of [Ca]i by InsP3 leads to activation of Cl- channels involving cytosolic Ca2+ stores and Ca2+ influx from extracellular space. Tyrosine kinases are essential for the Ca2+-independent maintenance of this conductance.

Stimulation of maxi-K channels in trabecular meshwork by tyrosine kinase inhibitors

PURPOSE

Muscarinic agonists contract and tyrosine kinase inhibitors relax precontracted trabecular meshwork, a smooth muscle-like tissue involved in the regulation of aqueous humor outflow. The effect of tyrosine kinase inhibitors on membrane currents of cells stimulated by acetylcholine was examined.

METHODS

Cells from bovine trabecular meshwork were studied using both the perforated patch-clamp technique with nystatin and the single-channel technique.

RESULTS

Application of the tyrosine kinase inhibitor genistein (5 x 10(-5) M) on trabecular meshwork cells stimulated with acetylcholine resulted in a reversible increase in outward current to 578%+/-154% (n = 16) of the initial current level. The effect of genistein was dose dependent. Reversal potential was hyperpolarized by 15+/-3 mV (n = 9). Tyrphostin 51, a synthetic inhibitor of tyrosine kinases, had the same effect (433%+/-46%; n = 7). Daidzein, a nonactive structural analogue of genistein, had no effect (n = 4). The stimulation of outward current by tyrosine kinase inhibitors was blocked by substitution of tetraethylammonium (TEA+) for potassium, whereas the potassium channel blockers glibenclamide (K-ATP) and apamin (low-conductance calcium-activated potassium channel) had no effect. Blockage of the high-conductance calcium-activated potassium channel (maxi-K) by charybdotoxin or iberiotoxin (10(7) M) suppressed 86%+/-18% (n = 4) of the response. Depleting the cells of calcium did not have an effect on the current stimulated by genistein. In the excised inside-out configuration, open probability increased to 417%+/-39% (n = 3) after exposure to genistein.

CONCLUSIONS

In trabecular meshwork, tyrosine kinase inhibitors activate maxi-K (K(Ca)) channels. Hyperpolarization caused by efflux of potassium could lead to the relaxation of trabecular meshwork by tyrosine kinase inhibitors.

Altered regulation of L-type channels by protein kinase C and protein tyrosine kinases as a pathophysiologic effect in retinal degeneration

The effect of protein tyrosine kinases (PTK) on L-type calcium channels in cultured retinal pigmented epithelium (RPE) from rats with retinal dystrophy was investigated. Barium currents through Bay K 8644 (10(-6) M) sensitive L-type channels were measured using the patch-clamp technique. The current density of L-type currents is twice as high and the inactivation time constants are much slower than in cells from nondystrophic control rats. Application of the PTK blockers genistein, lavendustin A, and herbimycin A (all 5 x 10(-6) M) led to an increase of L-type currents. Intracellular application of pp60c-src (30 U/ml) via the patch pipette led to a transient decrease of L-type currents. The protein kinase A (PKA) and PKG blocker H9 (10(-6) M) showed no effect on L-type currents. However, the protein kinase C blocker chelerythrine (10(-5) M) reduced these currents. Up-regulation of PKC by 10(-6) M 4beta-phorbol-12 myristate-13 acetate (PMA) led to a decrease of L-type currents. Additional application of genistein led to a further decrease of these currents. However, intracellular application of pp60(c-src) in PMA-treated cells led to a transient increase of L-type currents. Investigating the calcium response to bFGF application showed that RPE cells from RCS rats used different pathways than control RPE cells to increase cytosolic free calcium. This different pathway does not involve the activation of L-type channels. The present study with RPE cells from rats with retinal dystrophy shows a changed integration of PTK and PKC in channel regulation. Considering the altered response to bFGF in RCS-RPE cells, this disturbed regulation of L-type channels by tyrosine kinases is involved in the etiology of retinal degeneration in RCS rats.

Role of protein tyrosine kinase on regulation of trabecular meshwork and ciliary muscle contractility

PURPOSE

Trabecular meshwork and ciliary muscle express properties of smooth muscle cells. The contractility of trabecular meshwork and ciliary muscle is differently modulated by various agents. To reveal contractile regulatory processes, the effects of activation and inhibition of protein tyrosine kinases (PTKs) and their interaction with other protein kinases on contractility were measured.

METHODS

Measurements of isometric tension were performed on isolated bovine trabecular meshwork and ciliary muscle strips using a custom-built, electromagnetic, force-length transducer. Protein tyrosine kinase (PTK) was stimulated by epidermal growth factor (EGF) and was inhibited by genistein or tyrphostin 51. Protein kinase C (PKC) was inhibited by chelerythrine or NPC-15437 and protein kinases A and G (PKA-PKG) by H8.

RESULTS

Isolated strips were precontracted by applying carbachol 10(-6) M for 30 minutes (100% carbachol maximum contraction). Inhibition of PTK evoked a maximum relaxation of 79.2+/-4.2% in trabecular meshwork and of 38.1+/-3.1% in ciliary muscle (n=8). Inhibition of PKC or PKA-PKG induced relaxations only in trabecular meshwork. When PTK and PKC or PKA-PKG were inhibited, the relaxation induced by inhibition of PTK was additive to inhibition of the other protein kinases. Stimulation of a receptor with PTK activity by EGF induced a relaxation in trabecular meshwork and a contraction in ciliary muscle precontracted by carbachol. When trabecular meshwork and ciliary muscle were activated by EGF, inhibition of PTK by genistein relaxed the cell preparations.

CONCLUSIONS

Inhibition of PTK induces more prominent relaxation in trabecular meshwork than in ciliary muscle. The effects of inhibition of PTK on relaxation are independent of inhibition of PKC and PKA-PKG. The signaling cascade after activation of a tyrosine kinase receptor by EGF is differently modulated in trabecular meshwork and ciliary muscle. The effect of genistein on relaxation is probably not directly related to the EGF receptor. PTK inhibitors are possible agents for the development of novel antiglaucoma drugs.

Activation of a Cl--conductance by protein kinase-dependent phosphorylation in cultured rat retinal pigment epithelial cells

While chloride conductances are involved in signals of the electroretinogram generated by the retinal pigment epithelium (RPE), patch-clamp experiments of freshly isolated or cultured RPE cells have shown that potassium conductances predominate. The purpose of this study was to investigate mechanisms which activate Cl--conductances in RPE cells. Membrane currents of cultured rat RPE cells were measured using the whole-cell configuration of the patch-clamp technique under extra- and intracellular K+-free conditions. The bath solution was hyperosmolal to the pipette solution to prevent hypoosmotic swelling. Exchange of the physiological intracellular fluid by a pipette solution with physiological levels of ATP (2 mm) induced a continuous increase of membrane conductance. Conductance was blocked by DIDS (1 mm), and showed a reversal potential close to the Nernst potential for Cl-. When the experiments were carried out under conditions in which all cations, and not only potassium, were replaced by NMDG, the same responses could be observed. Current activation was independent of extracellular calcium. Chloride currents were also induced when ATPgammaS or AMP-PNP were used instead of ATP. In the presence of AMP-PNP currents were 10 times smaller than in the presence of ATP or ATPgammaS. In cells preincubated with staurosporine or chelerythrine no currents were induced. Establishing the whole-cell configuration with ATP and with myristoylated PKC substrate in addition, no voltage-dependent currents were activated. We conclude that ATP hydrolysis leads to activation of chloride currents via PKC in the whole-cell configuration. The perforated patch configuration, with the intracellular compartment intact, no currents were induced under otherwise identical experimental conditions. Inhibition of phosphatase by calyculin (10 nm) in the perforated-patch configuration did not change membrane conductance. In the intact cell, chloride conductance is possibly inhibited by a cytosolic factor which is washed out when the whole-cell configuration is established.

Regulation of L-type calcium channels by protein tyrosine kinase and protein kinase C in cultured rat and human retinal pigment epithelial cells

The effect of protein tyrosine kinases (PTKs) on L-type calcium channel currents was studied in cultured rat and human retinal pigment epithelial cells. Barium currents through L-type channels were measured in the perforated patch-clamp technique and identified by using the L-type calcium channel opener Bay K8644 (10(-6) M). Application of the PTK blockers genistein (5 x 10(-6) M) or lavendustin A (5 x 10(-6) M) led to a decrease of L-type currents. The inactive genistein analog daidzein (10(-5) M) showed no effect on calcium channels. Intracellular application of pp60(c-src) (30 U/ml) via the patch-pipette during the conventional whole-cell configuration led to an increase of L-type currents. The protein kinase A and protein kinase G blocker H9 (10(-6) M) showed no effect on L-type currents; genistein reduced the current in the presence of H9. The protein kinase C (PKC) blocker chelerythrine (10(-5) M) reduced the L-type current; additional inhibition of PTK by lavendustin showed an additional reduction of currents. Intracellular application of myristoylated PKC substrate (5 x 10(-5) M) for PKC inhibition led to a fast rundown of L-type current amplitudes. Intracellularly applied myristoylated PKC substrate (10(-4) M) together with pp60(c-src) showed no effect on L-type current. Up-regulation of PKC by 10(-6) M phorbol-12-myristate-13-acetate (PMA) had no effect on the L-type current amplitude. However, genistein in cells pretreated with PMA led to an increase of the L-type currents. Intracellular application of pp60(c-src) in PMA-treated cells led to a reduction of L-type currents. We conclude that in the resting cell, PTK and PKC regulate L-type calcium channels in an additive manner. L-type channels appeared as a site of integration of PTK activation and of PKC-dependent pathways. The activity of PKC determines whether PTK decreases or increases L-type channel activity.

Characterization of maxi-K-channels in bovine trabecular meshwork and their activation by cyclic guanosine monophosphate

PURPOSE

Electrophysiological characterization of trabecular meshwork cells and investigation of their response to elevation of cytosolic cyclic guanosine monophosphate (cGMP).

METHODS

Bovine trabecular meshwork cells were cultured according to established methods and were studied, using the whole-cell and single-channel configurations of the patch-clamp technique.

RESULTS

In single-channel experiments, cells expressed a channel with characteristics typical of maxi-K-channels. The channel was densely distributed in the membrane and had a high conductance of 326 +/- 4 pS (Pico Siemens) (symmetrical 150 mmol/l KCl; 37 degrees C) for potassium and negligible conductance for sodium (0.9 +/- 1 pS). The open probability could be elevated by depolarization, increasing cytosolic calcium, or adding adenosine triphosphate (1 mmol/ l). The channel could be blocked by external charybdotoxin (10(-8) mol/1), external TEA+ tetraethyl ammonium chloride (1 mmol/l) and by internal Ba2+ (10 mmol/l), whereas external Ba2+ and internal TEA+ (10 mmol/l) had no effect. In whole-cell experiments, trabecular meshwork cells displayed a strong outward conductance. Part of this conductance (35 +/- 5%) could be blocked by charybdotoxin and stimulated by ionomycin (10(-5) mol/1). Addition of 8-bromo-cGMP (10(-3) mol/1) stimulated the current to 290 +/- 57% (n = 4) of the original level, charybdotoxin led to a reduction of this current to 156 +/- 28% of the initial value.

CONCLUSIONS

Trabecular meshwork cells express maxi-K-channels. These channels can be stimulated by raising internal cGMP levels and are known for their importance in smooth muscle relaxation. The results in this study supply further evidence that trabecular meshwork displays smooth muscle-like properties and contributes to the clarification of the mechanism leading to the relaxation of trabecular meshwork by nitrate and nonnitrate vasodilatators.

Activation of Cl- currents in cultured rat retinal pigment epithelial cells by intracellular applications of inositol-1,4,5-triphosphate: differences between rats with retinal dystrophy (RCS) and normal rats

Using the whole-cell configuration of the patch-clamp technique, we studied the conditions necessary for the activation of Cl--currents in retinal pigment epithelial (RPE) cells from rats with retinal dystrophy (RCS) and nondystrophic control rats. In RPE cells from both rat strains, intracellular application of 10 microM inositol-1, 4,5-triphosphate (IP3) via the patch pipette led to a sustained activation of voltage-dependent Cl- currents, blockable by 1 mm 4, 4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS). IP3 activated Cl- currents in the presence of a high concentration of the calcium chelator BAPTA (10 mM) in the pipette solution, but failed to do so when extracellular calcium was removed. Intracellular application of 10(-5)M Ca2+ via the patch pipette also led to a transient activation of Cl- currents. When the cells were preincubated in a bath solution containing thapsigargin (1 microM) for 5 min before breaking into the whole-cell configuration, IP3 failed to activate voltage-dependent currents. Thus, IP3 led to release of Ca2+ from cytosolic calcium stores. This in turn activated an influx of extracellular calcium into the submembranal space by a mechanism as yet unknown, leading to an activation of calcium-dependent chloride currents. In RPE cells from RCS rats, which show an increased membrane conductance for calcium compared to normal rats, we observed an accelerated speed of Cl--current activation induced by IP3 which could be reduced by nifedipine (1 microM). Thus, the increased membrane conductance to calcium in RPE cells from RCS rats changes the response of the cell to the second messenger IP3.

Incomplete belts of tight junctions in cultured non-pigmented human ciliary epithelial cells

Tight junctions of cultured human non-pigmented ciliary epithelial cells were studied with the freeze-fracture technique and related to the transepithelial electrical resistance of these monolayers. Isolated tight junctional fibrils or small groups and networks of tight junctions sometimes associated with gap junctions were revealed in freeze-fracture images of the lateral plasma membrane. The tight junctions always formed incomplete belts, so that the apical and basolateral plasma membrane domains often were in continuity without morphological evidence of interposed intercellular junctions. The monolayers revealed a transepithelial resistance of 19.7 +/- 2.1 omega.cm2. Protamine induced a reversible increase of the transepithelial resistance of the cultures by 91 +/- 12%, but still the tight junctions formed incomplete belts. We conclude that contrary to complete networks of tight junctions in native non-pigmented ciliary epithelium, cultured monolayers only express incomplete belts of tight junctions which may be the morphological correlate of the relatively low transepithelial resistance of these monolayers. Interpretations on transepithelial transport and permeability characteristics of these cultures have to take into account the differences in junctional morphology from their native epithelium.

Potassium currents in cultured cells of the rat retinal pigment epithelium

Whole-cell currents were investigated in cultured rat retinal pigment epithelial (RPE) cells. Two voltage-dependent conductances were discriminated. First, at potentials more positive than -30 mV, a time-dependent outward current was activated. Inhibition by Ba2+ (10 mM) and 4-aminopyridine (10 mM) indicated that this current was carried by potassium ions. This current showed no inactivation during 5 sec depolarizations. Second, an inward current, sensitive to Ba2+ (10 mM) and 4-aminopyridine (10 mM), was activated at potentials more negative than -70 mV. Under extra- and intracellular potassium-free conditions, both currents disappeared. In summary, cultured rat RPE cells expressed one potassium conductance similar to the delayed rectifier and one similar to the inward rectifier. The delayed rectifier expressed characteristics comparable with those known in mammalian species and different from those in non-mammalian species.

Extracellular matrix proteins as substrate modulate the pattern of calcium channel expression in cultured rat retinal pigment epithelial cells

We investigated the effect of different culture substrates on the expression of membrane conductances for calcium in cultured rat retinal pigment epithelial (RPE) cells using the perforated patch technique and barium as charge carrier. In younger cultures (up to 12 days old) the RPE cells expressed L-type calcium channels, in older cultures (more than 12 days old) LVA-type channels. The LVA-type channels have been characterized as a tetrodotoxin sensitive Ca2+ channels. Coating the culture substrate with laminin, shifted the culture age for expression of LVA-type channels to 7 days. When collagen type 4 was used as substrate LVA-type channels and L-type channels were expressed simultaneously in 7 days old cultures. We concluded that proteins of the extracellular matrix which are known to enhance cell differentiation in culture, enhance the expression of LVA-type channels in RPE cells.

Ca(2+)-conductances in cultured rat retinal pigment epithelial cells

Membrane conductances for Ca2+ in cultured rat pigment epithelial cells were studied in the whole-cell configuration of the patch-clamp technique using barium (10 mM) as a charge carrier. Two types of voltage-dependent and verapamil- and diltiazem-sensitive Ba2+ currents were observed. First, a nearly sustained current was activated by depolarization to potentials more positive than -30 mV and blocked by nifedipine (1 microM). This current was observed in cells of primary cultures less than 13 days old. Second, a transient nifedipine (1 microM) insensitive current was activated by depolarization to potentials more positive than -55mV in cultures which were more than 13 days old. This current was not carried by sodium and blocked by 1 microM tetrodotoxin (TTX). In summary, cultured rat retinal pigment epithelial cells in younger primary cultures express Ba2+ currents indicating the presence of L-type Ca2+ channels. In older primary cultures a low-voltage activated channel was observed with properties different from T-type calcium channels or TTX-sensitive calcium conducting sodium channels.

Cultured retinal pigment epithelial cells from RCS rats express an increased calcium conductance compared with cells from non-dystrophic rats

The Royal College of Surgeon (RCS) rats suffer from a retinal dystrophy that is caused by a malfunction of the retinal pigment epithelium (RPE). We compared the membrane currents of cultured RPE cells from non-dystrophic and RCS rats by using the whole-cell configuration of the patch-clamp technique. Cultured RPE cells from RCS rats showed voltage-dependent, barium- and 4-aminopyridine-sensitive outward currents, which had characteristics of the delayed-rectifier and voltage-dependent, barium- and 4-aminopyridine-sensitive inward currents, which had characteristics of the inward rectifier. Differences between RPE cells from RCS rats and normal rats were as follows. (a) Cultured RCS rat RPE cells showed a resting potential and an activation threshold for the voltage-dependent outward current significantly more positive than that found in cells from non-dystrophic rats. (b) In the presence of 10 mM barium, the voltage-dependent outward current was reduced in both types of cells; in cells from RCS rats, an additional voltage-dependent inward current was observed. (c) This additional inward current had characteristics of L-type calcium channels and was reduced by verapamil (30 microM) and diltiazem (30 microM). In summary, we conclude that the membrane conductances of RPE cells from normal and RCS rats are dominated by potassium conductances. In contrast to cells from non-dystrophic rats, cells of RCS rats expressed an increased membrane conductance for calcium.

Voltage-dependent potassium currents in cultured human retinal pigment epithelial cells

Membrane currents in primary cultures of human retinal pigment epithelial cells were studied using the whole-cell configuration of the patch-clamp technique. Two types of voltage-dependent whole-cell currents were observed. First, a time- and voltage-dependent outward current, which was activated by depolarizing the cell to potentials more positive than -30mV, was sensitive to Ba2+ (10mM), 4-aminopyridine (10mM) and TEA+ (30mM). Tail-current analysis indicated that the current was mainly carried by K(+)-ions. Second, hyperpolarization of the cell to potentials more negative than -70mV led to a time- and voltage-dependent inward current which was blocked by Ba2+ (10mM) and 4-aminopyridine (10mM), but not by TEA+ (30mM). In summary, human retinal pigment epithelial cells in primary culture express currents which indicate the presence of a delayed rectifier K(+)-channel and an inward rectifier K(+)-channel.

Elevation of cytosolic free calcium in cultured ciliary epithelial cells by histamine: effects of verapamil and staurosporine

Treatment with histamine (10(-4) M) of cultured non-pigmented human ciliary epithelial cells led to a biphasic elevation of free intracellular calcium mediated by H1-receptors. The initial transient increase was due to Ca(2+)-release from intracellular calcium stores and could be blocked with a high concentration of verapamil (10(-4) M). The subsequent sustained elevation of cytoplasmic calcium caused by an influx of extracellular calcium was reduced by staurosporine (10(-7) M). We conclude that the sustained increase of cytoplasmic calcium by histamine may be partially mediated by activation of protein kinase C. Since depolarization of the cells had no effect on intracellular calcium, we conclude that typical voltage-operated calcium channels do not significantly influence intracellular calcium.

Transepithelial resistance of ciliary epithelial cells in culture: functional modification by protamine and extracellular calcium

1. Bovine pigmented and human non-pigmented ciliary epithelial cells were cultured on porous filter supports to obtain measurements of transepithelial electrical parameters. 2. The non-pigmented cells showed maximal transepithelial resistance of 15-30 omega cm2 from the third to seventh day in culture. 3. The pigmented ciliary cells reached maximal resistances of 9-20 omega cm2 after the fourth day in culture. 4. The transepithelial resistances of the cultured epithelia were functionally increased by protamine. This effect could be reversed by heparin. 5. We conclude that the range of resistances in cultured ciliary epithelial cells is the same as in whole ciliary preparations. Thus, cultured ciliary epithelial cells can be used for studies on transepithelial transport.