Abstract

The most important risk factor for the development of glaucoma is elevated intraocular pressure (IOP). Hypotensive drugs decrease IOP, preventing optic nerve damage and further vision loss. The balance between aqueous humor (AH) production and drainage determines IOP, and problems in AH outflow pathways are associated with open-angle glaucoma development. Previous studies have shown the presence of diadenosine tetraphosphate (Ap₄A) and pentaphosphate (Ap₅A) in the AH. Topic application of Ap₄A to the cornea decreased IOP, whereas Ap₅A increased it. Because dinucleoside polyphosphates stimulate P2Y purinergic receptors, we studied their presence in trabecular meshwork (TM) cells. Additionally, the effects of diadenosine polyphosphates (Ap_nAs; n = 3–5) and Up₄U (P¹,P⁴-(diuridine 5′)-tetraphosphate; INS365) in outflow facility were tested. P2Y₁, P2Y₂, and P2Y₄ receptors were detected in TM cells by Western blot and immunocytochemistry. In TM cells, Ap₃A, Ap₄A, and Ap₅A induced discrete intracellular calcium concentration ([Ca²⁺]_i) mobilizations compared with higher and more sustained [Ca²⁺]_i mobilizations after Up₄U application. In bovine ocular anterior segments perfused at constant pressure, 1 μM Ap₃A or Ap₄A increased outflow facility, whereas Up₄U or Ap₅A did not modify it. 2-MeSADP, a selective P2Y₁ agonist, induced outflow facility increases similar to those obtained after Ap₃A and Ap₄A, and these were prevented by addition of the selective P2Y₁ receptor antagonist MRS-2179 (2′-deoxy-N₆-methyladenosine-3′,5′-diphosphate). Our results demonstrate that the hypotensive effect of Ap₄A and other dinucleotides is mediated, at least in part, by increasing trabecular outflow facility through activation of P2Y₁ receptors. The latter would seem to be an interesting target in the development of antiglaucomatous drugs to selectively increase AH outflow.