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PubMed2001

Timolol may inhibit aqueous humor secretion by cAMP-independent action on ciliary epithelial cells.

The beta-adrenergic antagonist timolol reduces ciliary epithelial secretion in glaucomatous patients. Whether inhibition is mediated by reducing cAMP is unknown. Elemental composition of rabbit ciliary epithelium was studied by electron probe X-ray microanalysis. Volume of cultured bovine pigmented ciliary epithelial (PE) cells was measured by electronic cell sizing; Ca(2+) activity and pH were monitored with fura 2 and 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein, respectively. Timolol (10 microM) produced similar K and Cl losses from ciliary epithelia in HCO/CO(2) solution but had no effect in HCO/CO(2)-free solution or in HCO/CO(2) solution containing the carbonic anhydrase inhibitor acetazolamide. Inhibition of Na(+)/H(+) exchange by dimethylamiloride in HCO/CO(2) solution reduced Cl and K comparably to timolol. cAMP did not reverse timolol's effects. Timolol (100 nM, 10 microM) and levobunolol (10 microM) produced cAMP-independent inhibition of the regulatory volume increase (RVI) in PE cells and increased intracellular Ca(2+) and pH. Increasing Ca(2+) with ionomycin also blocked the RVI. The results document a previously unrecognized cAMP-independent transport effect of timolol. Inhibition of Cl(-)/HCO exchange may mediate timolol's inhibition of aqueous humor formation.

Animals↗
PubMed1988

Extravascular foci of Trypanosoma vivax in goats: the central nervous system and aqueous humor of the eye as potential sources of relapse infections after chemotherapy.

Relapse of parasitaemia after drug treatment of trypanosome infection is normally attributed to drug-resistance on the part of the parasite, under-dosage of the drug or reinfection of the host. In addition, inaccessibility of parasites to drug through sequestration in privileged extravascular sites has been shown in the past to occur with Trypanosoma brucei, and we have obtained evidence that extravascular foci of T. vivax can also serve as a source of relapsing infections. Infection of goats with a West African stock of T. vivax resulted in severe illness, which was fatal if untreated. During the terminal stage of an acute infection, clinical signs of central nervous system involvement were apparent. Histologically, the choroid plexus was swollen and oedematous, and in some cases meningitis or meningoencephalitis was seen. Trypanosomes could be detected in the cerebrospinal fluid, and also extravascularly in the choroid plexus and meninges. In three cases they were present in the aqueous humor, associated with corneal cloudiness or opacity. Treatment of 2 goats with the trypanocidal drug diminazene aceturate eliminated parasitaemia, but infections in both relapsed about 6 weeks later, despite trypanosomes being undetectable in the bloodstream during the intervening period. We conclude that the relapse infections were caused by reemergence of trypanosomes from the CNS and/or the eye, where sequestered parasites may have been inaccessible to the trypanocide.

Animals↗
PubMed1996

Gene expression of the neurotrophic pigment epithelium-derived factor in the human ciliary epithelium. Synthesis and secretion into the aqueous humor.

PURPOSE: To study the expression of the neurotrophic pigment epithelium-derived factor (PEDF), a protein with neurotrophic and neuronal-survival activities, by the human ocular ciliary epithelium. METHODS: Total RNA extracted from human and bovine ocular tissues were screened by Northern blot analysis with cDNA probes for PEDF. Antibodies to PEDF were used to monitor its synthesis and secretion by metabolically labeling ciliary processes in vitro with 35S-methionine, followed by immunoprecipitation. Pigment epithelium-derived factor antibodies also were used to visualize the cellular distribution of PEDF along the human and bovine ciliary epithelium. Polymerase chain reaction (PCR) and reverse transcription (RT)-PCR was used to screen cDNA libraries of tissue and cell lines derived from the ciliary epithelium to demonstrate PEDF expression. RESULTS: From a subtractive library of the human ocular ciliary body, the authors identified a cDNA clone exhibiting nucleotide homology with the PEDF. Northern blot analysis indicated that PEDF transcripts are present in all the ocular tissues in the human eye; in the bovine eye, it is expressed preferentially in the retinal pigment epithelium. RT-PCR and PCR demonstrated that the PEDF gene is still transcriptionally active in cultured cell lines derived from the bilayer of the ciliary epithelium. Immunoprecipitation and Western blot (immunoblot) analyses with antisera to the PEDF protein demonstrated that a predominant PEDF form of 46 kDa is synthesized in the ciliary body and is secreted as a glycoprotein of 50 kDa. By indirect immunofluorescence and immunocytochemistry, PEDF antibodies decorated both cell types that comprise the ciliary epithelium (nonpigmented and pigmented) and, more distinctively, the plasma-membrane domain of nonpigmented cells in the pars plicata region. CONCLUSIONS: These results reveal a new site of synthesis (ciliary epithelium) and accumulation (aqueous humor) of PEDF, and they emphasize its potential importance as a trophic factor in the neuro-differentiated functions of the human ciliary epithelium.

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