Immunolocalization of prostanoid EP receptor isotypes in human trabecular meshwork.

Purpose. To assess the localization of the EP-type prostanoid receptors in the human trabecular meshwork (TM) and to determine their spatial distribution in relation to the contractile alpha-smooth muscle actin fibres. Methods. Cryosections of human anterior segments were obtained from 17 different donors and immunostained with different EP receptor subtype specific antibodies. Double staining for the EP2 receptor and smooth muscle actin was carried out. Western blots of TM protein samples were studied. Results. No specific staining for the EP, receptor was observed. The antibodies against the EP2 receptor revealed in all donors intense staining of human trabecular cells throughout the meshwork. EP3 receptor specific staining was not detected. EP4 immunostaining was confined to the corneoscleral region near Schwalbe's line. On western blots, the EP2 receptor was detected. In the posterior TM, the EP2 receptor staining was associated with the dense network of actin fibres. Conclusions. These immunocytochemical results present evidence that the EP2 receptor is the most abundantly expressed isotype of the PGE receptors in the human TM. This conclusion is in agreement with our previous findings at the transcript level. The relaxant responses of the TM to application of EP, receptor agonists, and flow enhancement evoked by prostaglandin PGE(1), may be explained by the close spatial association of the EP2 receptor with actin fibres.