The role of tear proteins in tear film stability in the dry eye patient and in the rabbit.

Abstract

Sigma receptors have been identified in the lacrimal glands of rabbits; stimulation of these receptors results in the modulation of protein secretion from acinar cells. 1–4 When acinar cells were incubated with various sigma ligands, it was established that increases and decreases in protein release could be used to identify agonists and antagonists.4 Following the application of a newly designed agonist, N,N-dimethyl-2-phenylethylamine HC1 (AF2975), to the rabbit eye, a statistically significant increase in total protein was observed, when compared to either baseline values or the fellow eye.3 Tears were collected, and protein fractions were separated into various fractions with the use of size-exclusion high-pressure liquid chromatography (SE-HPLC).4 In particular, a 23 min protein fraction (about 16–18 kDa) was found to increase by 150% and 90% at 10 and 60 min, respectively following the topical application of AF2975 (50 μl of 0.15%) to the rabbit eye. Other protein peaks also showed an increase, but much less than the 23 min peak. Following desalting and concentrating, it was possible to separate the 23 min protein peak from rabbit tears into five isoforms using isoelectric chromatofocusing and a protein standard with a pI of 4.6. The isoforms were acidic with pIs higher than 4.6; however, the 23 min protein peak has not been specifically identified, which would require determination of its amino acid sequence. The function of the small-molecular-weight 23 min protein fraction is not known, but has been contrasted to the human tear fraction commonly referred to as tear-specific prealbumin (TSP) or as proteins migrating faster than albumin (PMFA).5–7 KeywordsSurface TensionAcinar CellLacrimal GlandSigma ReceptorBreakup TimeThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.