2-(-2-Benzofuranyl)-2-imidazoline reciprocally regulates Th17/Treg balance induced by ischemic stroke in rats.

Our group previously showed that 2-(-2-benzofuranyl)-2-imidazoline (2-BFI) is a potent neuroprotective agent in the treatment of ischemic stroke in rats. As its mode of action was not well defined, we determined if its therapeutic effect includes altering an immune response to experimental ischemic stroke in rats. In the current study, 2-BFI significantly reduced stroke-induced brain infarct volume and it also decreased neurological deficits. Its anti-immune effects were determined based on flow cytometry measurements of both the 2-BFI-induced changes in the Th17/ Treg cell balance ratio and ELISA measurements of proinflammatory IL-17A and anti-inflammatory IL-10 cytokine expression levels in the brain and peripheral blood following ischemic strokes. 2-BFI blunted the stroke-induced increases in this ratio, which resulted from suppression of the rises in the Th17 cell number whereas the proportion of Treg cells increased. Stroke also induced increases in IL-17A expression levels whereas the IL-10 expression levels declined. 2-BFI treatment inhibited the rises in IL-17A expression levels whereas the corresponding declines in IL-10 were suppressed by this agent. Therefore, one of the neuroprotective effects of 2-BFI in the treatment of cerebral strokes stems from its suppression of rises in the Th17/Treg balance along with corresponding changes in related cytokines modulating development of this condition.

NF-κB feedback control of JNK1 activation modulates TRPV1-induced increases in IL-6 and IL-8 release by human corneal epithelial cells.

PURPOSE: The corneal wound healing response to an alkali burn results in dysregulated inflammation and opacity. Transient receptor potential vanilloid type1 (TRPV1) ion channel activation by such a stress contributes to this unfavorable outcome. Accordingly, we sought to identify potential drug targets for mitigating this response, in human corneal epithelial cells (HCEC). METHODS: SV40-immmortalized HCEC were transduced with lentiviral vectors to establish stable c-Jun N-terminal kinase1 (JNK1), nuclear factor-κB1 (NF-κB1), and dual specificity phsophatase1 (DUSP1) shRNAmir sublines. Immunoblotting evaluated the expression of NF-κB1, DUSP1, protein kinase Cδ (PKCδ), and the phosphorylation status of cell signaling mediators. Enzyme-linked immunosorbent assay (ELISA) evaluated interleukin-6 (IL-6) and interleukin-8 (IL-8) release. RESULTS: Capsaicin (CAP; a selective TRPV1 agonist), induced time-dependent activation of transforming growth factor-activated kinase 1 (TAK1) and mitogen-activated protein kinase (MAPK) cascades temporally followed by increased nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor, alpha (IκBα) phosphorylation, rises in both PKCδ protein levels and IL-6 and IL-8 release. All of these responses were blocked by the TAK1 inhibitor 5z-7-oxozeaenol (5z-OX). In the JNK1 subline, CAP failed to increase IL-6/8 release, but still stimulated NF-κB by 50%. In the NF-κB1 subline, these IL-6/8 responses were absent, JNK1 activation was attenuated and there was a concomitant increase in DUSP1 expression compared to the control. In the DUSP1 subline, JNK1 phosphorylation was enhanced and prolonged and accompanied by larger increases in IL-6/8 release. CONCLUSIONS: TRPV1 induced increases in IL-6/IL-8 release occur through TAK1 activation of JNK1-dependent and JNK1-independent signaling pathways. Their joint activation is required for NF-κB to elicit sufficient positive feedback control of JNK1/2 phosphorylation to elicit increases in IL-6/8 release. Such regulation depends on NF-κB modulation of DUSP1 expression levels and associated changes in PKCδ protein levels.

Epidermal growth factor receptor transactivation by the cannabinoid receptor (CB1) and transient receptor potential vanilloid 1 (TRPV1) induces differential responses in corneal epithelial cells.

Corneal epithelial injury induces release of endogenous metabolites that are cannabinoid receptor 1 (CB1) and transient receptor potential vanilloid 1 (TRPV1) agonists. We determined the functional contributions by CB1 and TRPV1 activation to eliciting responses underlying wound healing in human corneal epithelial cells (HCEC). Both the selective CB1 and TRPV1 agonists (i.e., WIN55,212-2 [WIN] and capsaicin [CAP], respectively) induced EGFR phosphorylation whereas either inhibition of its tyrosine kinase activity with AG1478 or functional blockage eliminated this response. Furthermore, EGFR transactivation was abolished by inhibitors of proteolytic release of heparin bound EGF (HB-EGF). CB1-induced Ca(2+) transients were reduced during exposure to either the CB1 antagonist, AM251 or AG1478. Both CAP and WIN induced transient increases in Erk1/2, p38, JNK1/2 MAPK and Akt/PI-3K phosphorylation status resulting in cell proliferation and migration increases which mirrored those elicited by EGF. Neither EGF nor WIN induced any increases in IL-6 and IL-8 release. On the other hand, CAP-induced 3- and 6-fold increases, which were fully attenuated during exposure to CPZ, but AG1478 only suppressed them by 21%. The mixed CB1 and TRPV1 antagonist, AM251, enhanced the CAP-induced rise in IL-8 release to a higher level than that elicited by CAP alone. In conclusion, CB1 and TRPV1 activation induces increases in HCEC proliferation and migration through EGFR transactivation leading to global MAPK and Akt/PI-3K pathway stimulation. On the other hand, the TRPV1-mediated increases in IL-6 and IL-8 release are elicited through both EGFR dependent and EGFR-independent signaling pathways.

Effects of tryptamine on active sodium and chloride transport in the isolated bullfrog cornea.

The effects of the serotonin analogue, tryptamine, on the active transepithelial transport of Na+ and Cl- in the in vitro bullfrog cornea were studied. Tryptamine, 1 mM, inhibited both the short-circuit current (Isc) and potential difference (PD) of corneas transporting either Na+ alone or both Na+ and Cl-. The electrical resistance, R, increased in all cases. Both unidirectional Na+ and Cl- fluxes were decreased by tryptamine and these changes accounted for the inhibitory effects on the Isc. The effects of tryptamine were considered along with those of 2 mM theophylline and 0.1 mM ouabain. Tryptamine inhibited the Isc and both undirectional Cl- fluxes which were previously stimulated by theophylline. Theophyline addition, after tryptamine preincubation, increases the Cl- undirectional fluxes but did not restore the inhibited Isc. The inhibitory effects of tryptamine on active Na+ and Cl- transport were different from those of ouabain. While both drugs inhibited the forward Na+ and Cl- fluxes, their backfluxes decreased with tryptamine and increased with ouabain. The addition to the bathing solution of tryptamine after ouabain preincubation reduced the ouabain-increased backward Cl- flux and further increased the electrical resistance. These results are analyzed in terms of an electrical model from which it appears that trypamine's mechanism of action was to decrease cellular permeability to the transepithelial movement of Na+ and Cl-.

NPPB inhibits the basolateral membrane K+ conductance in the isolated bullfrog cornea.

The effects of the Cl- channel blocker, 4-nitro-2-(3-phenylpropylamino)benzoate (NPPB) on active transepithelial Cl- transport were measured in the isolated bullfrog cornea. With a Cl(-)-free Ringers, stromal-side 10(-5) M NPPB elicited a maximum depolarization of the membrane voltage from -72 +/- 6 to -48 +/- 9 mV (n = 6, P less than 0.05) and reduced the magnitude of the depolarization induced by a 10-fold increase in K+ concentration. Subsequent exposure to 10(-4) M ouabain decreased the membrane voltage from -41 +/- 6 mV to -25 +/- 2 mV (n = 6, P less than 0.05). After stimulation with 10(-5) M amphotericin B of a short-circuit current, Isc, largely accounted for by tear to stroma K+ diffusion, this Isc was effectively inhibited by 10(-5) M NPPB on the stromal-side. This decrease reflected a fall in basolateral membrane K+ conductance. In NaCl Ringers, inhibition of the essentially Cl(-)-originated Isc either on the tear- or stromal-sides required instead 10(-4) M NPPB. NPPB depolarized the membrane voltage from -55 +/- 7 to -38 +/- 6 mV (n = 14, P less than 0.05). The direction of the change in the fractional apical membrane resistance (fRo) depended upon its initial value; in those corneas with a lower value it increased whereas if they had a higher fRo, 10(-4) M NPPB consistently caused fRo to fall. However, following exposure to 5 x 10(-3) M Ba2+ and a fall in fRo, NPPB consistently caused fRo to increase significantly from 30 +/- 8 to 53 +/- 4% (n = 5). Therefore, inhibition of active Cl- transport by 10(-4) M NPPB may be associated with declines in: (1) a basolateral membrane K+ conductance that is distinct from a Ba2(+)-sensitive pathway; (2) an apical membrane Cl- conductance. Neither of these effects may be the result of a direct effect of NPPB on a conductance pathway because: (1) the drug was equipotent from either bathing solution; (2) following a one hour washout the Isc had not fully recovered to its control value.

Changes in cellular membrane and paracellular conductances by amphotericin B in the epithelium of the bullfrog cornea.

In the isolated bullfrog cornea, measurements of DC electrical parameters in conjunction with AC impedance and ultrastructural analyses were used to determine the effects of 10(-5) M amphotericin B on epithelial cellular membrane and paracellular conductances. In NaCl Ringers, amphotericin B elicited a 3.5-fold increase in the specific apical membrane conductance (Ga/Ca); where Ga and Ca are the apical membrane conductance and capacitance, respectively. The basolateral membrane conductance (Gb) and the basolateral membrane capacitance (Cb) fell by 57% and 50%, respectively. In the paracellular pathway, the tight junctional complex (Gj) was unchanged whereas the lateral intercellular space resistance (Rp) decreased by 55%. The declines in Gb and Cb were suggestive of cell volume shrinkage because these changes were consistent with a previously described decline in intracellular K+ content and reduction in exposed basolateral membrane area to current flow. Ultrastructural analysis validated that amphotericin B caused cell volume shrinkage because there was: (1) increased folding of the basolateral membrane and waviness of the basal aspects- of the plasma membrane; (2) dilatation of the lateral intercellular spaces. This agreement suggests that intracellular activity decreased following exposure to amphotericin B which resulted in cell volume shrinkage and an impairment of Cl- uptake across the basolateral membrane.

Identification of calmodulin-sensitive Ca(2+)-transporting ATPase in the plasma membrane of bovine corneal epithelial cell.

ATP-dependent Ca2+ uptake was characterized in a plasma membrane enriched fraction obtained from the bovine corneal epithelium. This uptake essentially represented intravesicular accumulation because 72% of the Ca2+ content was releasable following exposure to 10(-6) M A23187. The substrate and Ca2+ requirements for maximal transport activity were similar to those described in the red blood cell because: (1) exogenous calmodulin (3 microM) significantly decreased the apparent Km for Ca2+ to 0.31 microM and increased the rate of Ca2+ uptake; (2) a hydroxylamine labile Ca(2+)-dependent phosphoenzyme intermediate was identified with an apparent molecular size of 140 kDa; (3) Ca(2+)-dependent binding of 125I-labelled calmodulin to this protein was demonstrated which could be antagonized with a calmodulin antagonist, trifluoperazine. These results show that the plasma membrane contains an ATP-dependent Ca2+ transporter. However, its relationship to a previously described high affinity form of Ca(2+)-stimulated Mg(2+)-dependent ATPase is not apparent because their [Mg2+] requirements to elicit maximal activity differed by two orders of magnitude.

Okadaic acid suppresses TPA-induced differentiation by stimulating G1/S transition in human myeloblastic leukaemia ML-1 cells.

The association between the phosphorylation status of the retinoblastoma protein, pRb and changes in cell cycle control caused by either protein kinase C (PKC) or protein kinase A (PKA) stimulation was evaluated in human myeloblastic leukaemia ML-1 cells. TPA-induced PKC activation resulted in dephosphorylation of pRb and subsequently induced ML-1 differentiation based on morphological changes and CD14 expression. In the present study, we showed that inhibition of protein phosphatases (PP-1 and PP-2a) prevented the TPA-induced differentiation in ML-1 cells. Preinhibition of PP-1 and PP-2a activities with 1-100 nM okadaic acid dose-dependently blunted the decrease in the phosphorylation status of pRb obtained with TPA and overrode cell cycle arrest. PKA stimulation with 8-chlorophenylthio-cAMP (100 microM) decreased cell proliferation by 65% and the distribution of cells in the G1 phase significantly increased from 38% to 83% concomitant with a 34% decline in the number of cells present in the S phase. In addition, PKA stimulation significantly decreased the pRb phosphorylation status but did not elicit CD14 expression, indicating that cAMP-induced dephosphorylation of pRb cannot by itself trigger differentiation in ML-1 cells.

Activation of a CFTR-mediated chloride current in a rabbit corneal epithelial cell line.

PURPOSE: To determine whether there is gene expression and functional activity of cystic fibrosis transmembrane conductance regulator protein (CFTR) in an SV40-immortalized rabbit corneal epithelial cell line, tRCE. METHODS: Both whole-cell and cell-attached patch-clamp techniques were used to examine the biophysical characteristics of the cAMP-dependent chloride current. The molecular identity of this conductance was evaluated using RT-PCR analysis. RESULTS: In whole-cell patch-clamp studies, a cAMP-dependent chloride conductance was further facilitated by the known CFTR activator genistein (20 microM). Kinetic analysis of cell-attached patches containing few channels ascertained that genistein increased the chloride channel activity by increasing channel open probability (via an increased channel open time and a decreased channel closed time). In addition, in the presence of a reduced forskolin concentration (i.e., 100 nM), the chloride conductance generated could be augmented by the nonspecific phosphodiesterase enzyme inhibitor, IBMX (100 microM), implicating the importance of intracellular cAMP in the regulation of this conductance. Furthermore, this conductance exhibited voltage-dependent inhibition in the presence of the CFTR chloride channel blocker glibenclamide (250 microM), but was DIDS insensitive (500 microM). Consistent with the presence of a CFTR-mediated chloride conductance, the expression of CFTR-mRNA was detected using RT-PCR. Sequence analysis of the product revealed 99.4% homology to that described for rabbit CFTR. CONCLUSIONS: In tRCE cells, there is gene expression and functional CFTR activity. Its presence may have important therapeutic implications in corneal epithelial diseases resulting from declines in transepithelial secretory and fluid transport activity.

Alpha 1-adrenoceptors in human corneal epithelium.

Specific binding of the potent, selective alpha 1-adrenoceptor antagonist 3H-prazosin was demonstrated in cultured human corneal epithelial cells. Specific binding of the radioligand was concentration-dependent between 0.5 and 6 nM, with apparent saturation of receptor sites seen at higher concentrations. The cells exhibited a maximum binding capacity for 3H-prazosin of 225 fmol/mg of cellular protein and a dissociation constant of 2 nM. The binding of 3H-prazosin was competitive with known alpha 1-adrenoceptor ligands and was reversible. Epithelium of intact human corneas also exhibited specific 3H-prazosin binding, as did cultures of bovine and rabbit corneal epithelium. The alpha-adrenergic agonist methoxamine significantly stimulated phosphatidylinositol 4,5-bisphosphate hydrolysis, measured as myoinositol trisphosphate accumulation in cultures of human corneal epithelium. This stimulation was inhibited by the presence of prazosin during the assays. These findings indicate the existence of specific, reversible, high-affinity receptors for alpha 1-adrenoceptors that regulate inositol phosphate turnover in human, rabbit, and bovine corneal epithelial cells.

Chloride compartments of the frog lens and chloride permeabilities of its isolated surfaces.

Total Cl content and exchangeable Cl pools of isolated bull frog lens and Cl permeabilities of its isolated anterior and posterior surfaces were determined. Cl content was 2.81 microEq, corresponding to a cellular concentration of 13.3 mM. After 18 hr. incubation Cl content increased to 3.84 microEq. Three Cl compartments were found: a fast compartment (t1/2 = 130 min.), probably extracellular; a slow compartment (+ 1/2 = 160 min.), probably intracellular; and a bound fraction (24% of the total Cl). 36Cl efflux across anterior and posterior lens surfaces was similar. However, when a correction for the asymmetrical electrical potential difference was made, the permeability of the posterior side, 46.9 x 10(-7) cm./sec., was nearly twice the permeability of the anterior side, 27.6 x 10(-7) cm./sec. The Cl movement and distribution seem to obey passive forces. Iodoaceta increased both total Cl and exhangeable Cl but had little effect on the rate of Cl exchange. Total Cl gain by lenses incubated at 2 degrees C was similar to the control. However, the exchangeable Cl pools and the rate of exchange were significantly diminished.

Endothelin-mediated cell signaling and proliferation in cultured rabbit corneal epithelial cells.

PURPOSE: To determine if there is endothelin-mediated regulation of cell signaling and proliferation in rabbit corneal epithelium. METHODS: Endothelin-1 (ET-1) gene and protein expression by the rabbit corneal epithelial (RCE) cells were analyzed by polymerase chain reaction, sequence analysis, and enzyme immunoassay. DNA synthesis was characterized by [3H]-thymidine uptake. Endothelin receptor linkage to cell signaling pathways was determined based on measurements of the dose dependent effects of ET-1, ET-2, and ET-3 on intracellular Ca2+ concentration ([Ca2+]i) transients in fura-2-loaded cells, and of ET-1 on phosphoinositide turnover and cAMP accumulation in the isolated rabbit corneal epithelium. RESULTS: The authors detected the mRNA for prepro ET-1 in RCE cells, and ET-like immunoreactivity was identified in conditioned culture medium. ET-1 (1 nM) maximally stimulated [3H]-thymidine uptake by twofold (EC50 = 0.3 nM). Endothelins elicited transient increases in [Ca2+]i with a rank order of potency of ET-1 > or = ET-2 >> ET-3. These increases consisted of both intracellular Ca2+ mobilization and influx of Ca2+ from the bathing solution. Intracellular mobilization was linked to increases in IP3 turnover because 1 microM ET-1 increased IP3 content by 48% from its control value (EC50 = 23 nM), whereas Ca2+ influx occurred through a non-L-type Ca2+ channel because preexposure to 1 microM nicardipine did not affect either the height or the duration of a [Ca2+]i transient. One micromolar of ET-1 was required to elicit a significant increase in cAMP accumulation of 69% from its control value. This increase was dependent on the presence of Ca2+ in the bathing solution and was comparable to and nonadditive with that of the Ca2+ ionophore, A23187 (1 microM). CONCLUSION: These data suggest that endothelin production by primary cultures of RCE cells can mediate an increase in cell proliferation through an ETA receptor subtype. This receptor subtype appears to be involved based on the rank order of potency of ETs to elicit [Ca2+]i transients, increases in phosphoinositide turnover, and cAMP accumulation.

Inhibitory effect of PGE2 on EGF-induced MAP kinase activity and rabbit corneal epithelial proliferation.

PURPOSE: To determine in rabbit corneal epithelial cells in culture whether epidermal growth factor (EGF)-induced increases in prostaglandin (PG) E2 production inhibit both the extracellular signal-regulated kinase 2 (Erk-2), a mitogen-activated protein kinase (MAPK), cascade activation, and the mitogenic response to this growth factor. METHODS: Serum starvation for 24 to 36 hours was used to synchronize cultures of SV40-transformed rabbit corneal epithelial (RCE) cells. The effects of exogenous PGE2, inhibition of PGE2 synthesis, and modulation of protein kinase A (PKA) activity on EGF-induced Erk-2 activation were assessed by immunoprecipitation, kinase assays, and Western blot analysis. PGE2 synthesis was measured by using enzyme-linked immunosorbent assay. [3H]-Thymidine incorporation was used to measure RCE cell proliferation rates. RESULTS: EGF (5 ng/ml) significantly increased PGE2 production in a time-dependent manner up to 94%+/-8% after 3 hours. EGF-induced PGE2 production was suppressed by AACOCF3, a phospholipase A2 (cPLA2) inhibitor. EGF-induced Erk-2 activation reached a maximal level at 15 minutes, followed by a decline toward the control level after 3 hours. In the presence of either PGE2 (50 microg/ml) or 8-CPT-cAMP (100 microM), the EGF-induced Erk-2 activation was lessened. PKA was activated by applications of EGF or PGE2 and suppressed by AACOCF3. On the other hand, either inhibition of PGE2 production with AACOCF3 or H-89, a PKA inhibitor, enhanced EGF-induced Erk-2 activity. Raf-1 activity was stimulated by EGF to maximal activity at 5 minutes and returned toward its control level after 60 minutes. As with the dependence of Erk-2 activity on PKA activity, in the presence of H-89, the EGF-induced Raf-1 activation was significantly enhanced. DNA synthesis was increased 59%+/-5% (n = 4) after EGF stimulation, indicating a mitogenic effect of EGF in RCE cells. Inhibition of cPLA2 activity with AACOCF3 increased DNA synthesis in RCE cells by another 64% relative to the effect of EGF alone. In contrast, with either PGE2 or 8-CPT-cAMP present the mitogenic response to EGF was totally suppressed. CONCLUSIONS: EGF-induced increases in PGE2 production dampened the mitogenic response to this growth factor. This suppression appears to be a consequence of PGE2-elicited increases in PKA activity, which leads to inhibition of EGF-induced activation of MAPK cascades at the level of Raf-1 and further affects downstream events including Erk-2. These results indicate that the mitogenic response to EGF in vivo in the proliferating basal cell layer may be dependent on the level of its PKA activity.

ETB and epidermal growth factor receptor stimulation of wound closure in bovine corneal epithelial cells.

PURPOSE: To determine if there is a heterogeneous pattern of endothelin (ET) receptor subtype (i.e., ETA and ETB) gene expression in the bovine corneal epithelium (BCE). To determine if ET receptor subtype stimulation increases the effectiveness of epidermal growth factor (EGF) to accelerate wound closure in a primary culture of bovine corneal epithelial cells (BCEC). METHODS: In situ hybridization histochemistry was used to characterize ETA and ETB gene expression in the BCE. A wound closure assay evaluated wound healing rates in BCEC after 4 to 7 days in culture. [3H] thymidine incorporation and MTT assay measured proliferation. RESULTS: ETA gene expression was appreciably higher in the basal cells than in the suprabasal cells, whereas the pattern for ETB was reversed. Epidermal growth factor (5 ng/ml) maximally increased wound closure by 145% above the control. With 5 ng/ml EGF, either 10(-9) M ET-1 or 10(-8) M sarafotoxin-6-c (s-6-c) increased wound closure by an additional 39% (P < 0.001) above that measured with 5 ng/ml EGF alone. BQ123 (10(-7) M) did not alter any of these effects of ET-1 or s-6-c. Epidermal growth factor stimulated wound closure through a selective increase in proliferation. Neither ET-1 nor s-6-c alone had any effect on proliferation or migration. CONCLUSIONS: Both ETA and ETB genes are expressed in BCE. However, in BCEC only, ETB stimulation increases the effectiveness of EGF to stimulate wound closure. This response was caused by an increase in cell migration rather than proliferation because, after treatment with mitomycin C, neither ET-1 nor EGF stimulated wound closure.

Endothelin receptor-mediated Ca2+ signaling and isoform expression in bovine corneal epithelial cells.

PURPOSE: Bovine corneal epithelial cells (BCEC) were cultured to determine whether endothelin (ET) receptor subtype stimulation affects ET isoform expression (ET-1, ET-2, and ET-3) through capacitative Ca2+ influx. To probe in the isolated bovine corneal epithelium (BCE) for ET isoform and ET (i.e., ETA and ETB) receptor gene expression. METHODS: [Ca2+]i transients were characterized with microfluorometry. Endothelin isoform and ET receptor gene expression were probed with RNase protection analysis. Enzyme-linked immunosorbent assay was used to measure levels of ET-1-like immunoreactivity (ET-1-LI) in conditioned medium. RESULTS: ET-1 (10(-6) M) increased [Ca2+]i more than twofold. After treatment with 10(-7) M alltrans retinoic acid (an inducer of differentiation), 10(-6) M sarafotoxin (S-6-c) (a selective ETB agonist), had a similar effect. Preincubation with either 5 microM U73122 (an inhibitor of IP8 formation) or 10 microM cyclopiazonic acid, which depletes intracellular Ca2+ store content, eliminated ET agonist-mediated [Ca2+]i increases. With a nominally Ca(2+)-free solution containing 10 microM cyclopiazonic acid, simultaneous 10(-6) M ET-1 and extracellular Ca2+ additions transiently increased [Ca2+]i twofold, whereas 10(-6) M S-6-c increased it by only 20%. This augmentation was eliminated by preexposure to either BQ123 (10 microM), selective ETA receptor antagonist, U73122 (5 microM), or SKF 96365 (3 x 10(-5) M), an inhibitor of stores-operated channels. ET-1, ET-2 isoforms, and ET receptor mRNAs were identified. S-6-c (10(-6) M) increased the level of ET-1-LI after 12 hours by approximately ninefold. CONCLUSIONS: In BCEC, capacitative calcium influx is involved in mediating a positive feedback relationship between ETB receptor stimulation and ET protein expression. Identification of ET-1 and ET-2 gene expression in BCE strengthens the notion that this regulation could be autocrine mediated.

Corneal epithelial wound healing.

One of the important functions of the cornea is to maintain normal vision by refracting light onto the lens and retina. This property is dependent in part on the ability of the corneal epithelium to undergo continuous renewal. Epithelial renewal is essential because it enables this tissue to act as a barrier that protects the corneal interior from becoming infected by noxious environmental agents. Furthermore, the smooth optical properties of the corneal epithelial surface are sustained through this renewal process. The rate of renewal is dependent on a highly integrated balance between the processes of corneal epithelial proliferation, differentiation, and cell death. One experimental approach to characterize these three aspects of the renewal process has been to study the kinetics and dynamics of corneal re-epithelialization in a wound-healing model. This effort has employed in vivo and in vitro studies. From such studies it is evident that the appropriate integration and coordination of corneal epithelial proliferation, adhesion, migration, and cell demise is dependent on the actions of a myriad of cytokines. Our goal here is to provide an overview into how these mediators and environmental factors elicit control of cellular proliferation, adhesion, migration, and apoptosis. To this end we review the pertinent literature dealing with the receptor and the cell signaling events that are responsible for mediating cytokine control of corneal epithelial renewal. It is our hope that a better appreciation can be obtained about the complexity of the control processes that are responsible for assuring continuous corneal epithelial renewal in health and disease.

Differential expression of Na:K:2Cl cotransporter, glucose transporter 1, and aquaporin 1 in freshly isolated and cultured bovine corneal tissues.

Little is known about whether culturing corneal limiting layers causes changes in the expression of their membrane transporter proteins from those present in fresh tissues. Accordingly, we compared mRNA abundance of three well-described types of transporters: water channel aquaporin 1 (AQP1), glucose transporter (GLUT1), and Na:K:2Cl cotransporter (NKCC), as well as NKCC protein levels in fresh bovine corneal epithelium and endothelium with those in their cultured counterparts. Abundance of mRNA encoding AQP1, GLUT1, and NKCC was quantified by a lysate nuclease protection assay. NKCC transcription was further characterized by Northern blotting. All data were normalized to cell DNA and protein contents. In the fresh epithelium, in all three cases mRNA levels were two to four times higher than in the endothelium. Expression of AQP1 and GLUT1 was 10 to 12 times higher than that of NKCC. After the third passage, the endothelial cell mRNA abundance in each case decreased 2- to 3-fold. Passage-dependent decreases were also observed in NKCC protein expression in the epithelial cells. In both corneal layers, there was a qualitative correlation between NKCC mRNA and protein levels. Both in fresh and cultured epithelial and endothelial cells, a shark NKCC1 DNA probe hybridized with mRNAs of two different lengths (about 5.0-5.5 and 7.0-7.5 kb). An anti-NKCC T4 monoclonal antibody recognized two major proteins with apparent molecular masses of 190 to 200 and 150 to 160 kDa. In summary, membrane transporter function in culture may not be always indicative of their role in fresh tissue since in cultured cells AQP1, GLUT1, and NKCC mRNA levels declined. Furthermore, in both epithelial and endothelial cells, there is expression of two different proteins and mRNAs that possibly encode for secretory (NKCC1) and absorptive (NKCC2) isoforms.

Fluid transport by cultured corneal epithelial cell layers.

BACKGROUND/AIMS: Fluid transport across the in vitro corneal epithelium is short lived, hence difficult to detect and characterise. Since stable rates of fluid transport across several cultured epithelial cell layers have been demonstrated, the behaviour of confluent SV40 transformed rabbit corneal epithelial cells (tRCEC) grown on permeable supports was examined. METHODS: Fluid transport was determined with a nanoinjector volume clamp; the specific electrical resistance of the layers was 184 (SEM 9) Omega cm(2). tRCEC layers transported fluid (from basal to apical) against a pressure head of 3 cm H(2)O for 2-3 hours. RESULTS: In the first hour, the rate of fluid transport was 5.2 (0.5) microl/h/cm(-2) (n=23), which is comparable with that found in other epithelia. Fluid transport was completely inhibited in 15-30 minutes by either 100 microM ouabain (n=6), 50 microM bumetanide (n=6), or 1 microM endothelin-1 (ET-1; n=6). Preincubation with 10 microM BQ123 (an ET(A) receptor antagonist) obviated inhibition by ET-1 (n=6). ET-1 also caused a 22% decrease in specific resistance. CONCLUSIONS: Fluid transport appears to depend on transepithelial Cl(- )transport since (1) their directions are the same (stroma-->tear), and (2) both bumetanide and ouabain inhibit it with similar time course. tRCEC appear useful to investigate aspects of the physiology and pharmacology of fluid transport across this layer, including receptor mediated control of this process.

Roles of cyclic AMP and Ca in epithelial ion transport across corneal epithelium: a review.

The messenger roles of cyclic AMP and the calcium ion in stimulus-secretion coupling are considered in the frog and bovine corneal epithelium, respectively. In the frog cornea, epinephrine stimulates net C1 transport by increasing cyclic AMP content. This stimulation is associated with a larger apical membrane C1 conductance and basolateral membrane ionic conductance. The response of the apical membrane conductance is thought to result from an increase in cyclic AMP content whereas the basolateral membrane ionic conductance increase is unrelated based on measurements of the effects of the calcium channel antagonist, diltiazem, and the beta agonist, isoproterenol, on the electrical parameters and cyclic AMP content. The basolateral membrane is essentially K permselective since the K channel blocker, Ba, depolarized the intracellular potential difference and increased the basolateral membrane resistance. Diltiazem had even larger effects on these parameters suggesting that this compound is a more effective inhibitor of K channel activity than barium. In broken cell preparations of bovine corneal epithelium, a high affinity form of Ca + Mg activated ATPase is present (Km = .06 microM for Ca) and is essentially of plasma membrane origin. This ATPase activation is at a Ca activity similar to the expected intracellular value and suggests that this activity is the enzymatic basis for net Ca transport.

Endothelin-1 promotes corneal epithelial wound healing in rabbits.

This study is an attempt to determine the effect of endothelin-1 (ET-1)-containing eyedrops on the rate of corneal epithelial wound closure in rabbits. After corneal epithelial debridement of about 50-60 mm2 with n-heptanol, eyedrops containing either 10(-8) M ET-1 or 10(-6) M ET-1 were applied at five different times for the next three days. The wound was serially photographed 12, 24, 36, 48, 60 and 72 hours later to measure the extent of healing with a computerized planimeter. The respective wound healing rate at 10(-6) and 10(-8) M ET-1 was 1.293 +/- 0.040 mm2/hour (n = 11) and 1.262 +/- 0.087 mm2/hour (n = 6), respectively. These rates were 29% (p < 0.01) and 26% (p < 0.05) above the control value, 1.005 +/- 0.063 mm2/hour (n = 13). Reepithelialization was not associated with any epithelial hyperplasia, neovascularization or conjunctival hyperemia. These results suggest that ET-1-containing eyedrops could be of therapeutic value in the remedy of corneal epithelial defects.