Abstract
Purpose: :
The purpose of the study was to identify the expression of histamine (H) receptor subtypes in conjunctival goblet cells and determine their role in goblet cell secretion.
Methods: :
Goblet cells cultured from rat conjunctiva were homogenized and Western blotting analysis performed to identify H1, H2, H3, and H4 receptor subtypes. The cultured goblet cells were incubated with histamine at increasing concentrations (10-11-10-5 M) for 2 hrs and the amount of glycoconjugate secreted into the medium measured by an enzyme linked lectin assay (ELLA). Cultured goblet cells were also preincubated with the H1 receptor antagonist epinastine (10-6-10-3 M) or the H2 receptor antagonist cimetidine (10-6-10-3 M) followed by stimulation with histamine (10-5 M) for 2 hrs. The media were collection for analysis of glycoprotein secretion, which was standardized to the amount of protein in each culture well.
Results: :
H1, H2, H3 and H4 receptors were expressed in the cultured conjunctival goblet cells. Histamine increased the secretion of glycoprotein in concentration-dependent manner with a maximum increase of 5.6 fold above basal by histamine at 10-5 M. The H1 receptor antagonist, epinastine (10-4 M), suppressed the goblet cell secretion by 31%. Conversely, the H2 receptor antagonist cimetidine (10-4 M) increased basal secretion by 6-fold above basal and histamine-stimulated secretion by 7-fold above basal levels.
Conclusions: :
The H1 receptor may facilitate conjunctival goblet secretion, whereas the H2 receptor may play an inhibitory role.
Keywords: conjunctiva • ocular irritancy/toxicity testing • glycoconjugates/glycoproteins