Vanadate is an effective ocular hypotensive agent when given either topically or by the systemic route. Preliminary findings show that vanadate acts as a biological synergist at the level of protein phosphorylation, and that the intraocular pressure effect is not due to direct inhibition of Na+/K+ -ATPase. The overall objective of this project is to define the mechanisms for vanadate reduction of aqueous humor flow. Vanadate is a unique probe to investigate fundamental molecular regulation of function in ciliary processes by enzymes that dephosphorylate phosphoproteins.
The specific aims of the project involve both biolgoical and biochemical investigations designed to answer questions relating to vanadate's biological effects in the eye as follows: (1) The ocular penetration of vanadate in various forms (complexes oxidation state, etc.). (2) Interaction of vanadate with drugs acting on the sympathetic system, both at the receptor level and at the second messenger level (adenylate cyclase, Ca2+). The in vivo drug combination experiments will involve aqueous humor flow measurements and blood flow studies and will also utilize the lasered monkey eye and rabbit eye glaucoma models. Biochemical studies on vanadate/vanadyl effects on enzyme systems involved in regulation of ciliary process function will be done. These 3 studies will focus on stimulus-independent phosphoprotein phospatases. These enzymes which are inhibited by vanadate have not been studied at all in ciliary processes. They will be isolated and fully characterized. (4) A detailed investigation (with the ultimate objective of isolation and identification) of stimulus- dependent phosphorylation of specific proteins in ciliary processes and isolated epithelial cells, and the phosphorylation response to vanadate (synergistic or antagonistic with the stimulus) will be undertaken. The long range goal of this study is to establish the molecular bases for regulation of aqueous humor secretion by ciliary processes and new approaches to glaucoma therapy.
