Alterations in arachidonic acid release and phospholipase C-beta(1) expression in glaucomatous human ciliary muscle...

Prostaglandin (PG) F(2alpha) and other Ca(2+)-mobilizing agonists, such as carbachol (CCh) and endothelin (ET)-1, induce an increase in uveoscleral outflow, in part through receptor-mediated mechanisms in the ciliary muscle. Because changes in uveoscleral outflow across the ciliary muscle could cause elevation of intraocular pressure (IOP) in patients with glaucoma, the present study was conducted to investigate the possibility that basal and agonist-induced second-messenger formation may be altered in glaucomatous human ciliary muscle (g-HCM) cells compared with normal (n)-HCM cells.

Normal and glaucomatous HCM cells were cultured from donor eyes, the cells were identified based on their positive immunostaining with smooth muscle-specific anti-alpha-actin (SM), anti-SM-myosin, and anti-desmin antibodies. Activation of phospholipase A(2) (PLA(2)) was measured by the release of [(3)H] arachidonic acid (AA) into the medium, accumulation of PGE(2) was measured by radioimmunoassay, [(3)H]myo-inositol phosphate production was measured by ion-exchange chromatography, and phospholipase C (PLC)-beta(1) expression was determined by immunoblot analysis with polyclonal antibodies specific for PLC-beta(1).

Homogenous primary cell cultures from normal and glaucomatous human ciliary muscle were established and characterized. The data obtained can be summarized as follows: Both n- and g-HCM cells exhibited similar morphologic characteristics and immunoreactivities. The effects of the agonists on AA release in both n- and g-HCM cells were in the following order: PGF(2alpha) > ET-1 > CCh; their effects on PGE(2) release were in the following order: PGF(2alpha) > CCh > ET-1; and their effects on inositol phosphate production were in the following order: CCh > ET-1 > PGF(2alpha). Both the basal- and stimulated release of AA were significantly higher in the g-HCM cells than in the n-HCM cells (for PGF(2alpha), 60% vs. 151%). The basal release of PGE(2) in g-HCM cells was two- to fivefold higher than that of n-HCM cells, and there are alterations in the effects of the agonists on PGE(2) release. Agonist-induced inositol phosphate production in g-HCM cells was considerably lower than that of n-HCM cells (CCh, 58% vs. 421%), and the amount of PLC-beta(1) expressed in g-HCM cells, compared with that in n-HCM cells, was markedly reduced (by 44%).

These data are the first to show that basal and agonist-induced AA release and inositol phosphate production as well as expression of PLC-beta(1) are altered in g-HCM cells compared with that of n-HCM cells. The molecular mechanisms underlying these alterations in g-HCM cells could include changes in sensitivity and number of receptors, overexpression of PLA(2) and the cyclooxygenases, and underexpression of PLC-beta(1). Alterations in these signaling pathways in g-HCM cells could contribute to changes in the uveoscleral outflow pathway, which may lead to an increase in IOP in patients with glaucoma. Comparative studies on the signaling pathways in g- and n-HCM cells can provide important information about the regulation of uveoscleral outflow and the pathologic course of glaucoma.