Regulation of lens beta-adrenergic receptors by receptor occupancy and dexamethasone

Lens gap junctions in growth, differentiation, and homeostasis

The cells of most mammalian organs are connected by groups of cell-to-cell channels called gap junctions. Gap junction channels are made from the connexin (Cx) family of proteins. There are at least 20 isoforms of connexins, and most tissues express more than 1 isoform. The lens is no exception, as it expresses three isoforms: Cx43, Cx46, and Cx50. A common role for all gap junctions, regardless of their Cx composition, is to provide a conduit for ion flow between cells, thus creating a syncytial tissue with regard to intracellular voltage and ion concentrations. Given this rather simple role of gap junctions, a persistent question has been: Why are there so many Cx isoforms and why do tissues express more than one isoform? Recent studies of lens Cx knockout (KO) and knock in (KI) lenses have begun to answer these questions. To understand these roles, one must first understand the physiological requirements of the lens. We therefore first review the development and structure of the lens, its numerous transport systems, how these systems are integrated to generate the lens circulation, the roles of the circulation in lens homeostasis, and finally the roles of lens connexins in growth, development, and the lens circulation.

Enhanced ocular hypotensive response to epinephrine in rabbits with prior dexamethasone treatment

The purpose of this study was to determine glucocorticoid modulation of ocular pressure to epinephrine applied topically to rabbit eyes that were pretreated with dexamethasone. Rabbit eyes were pretreated with five applications of topical 0.07% dexamethasone (0.1% dexamethasone phosphate) or saline drops, administered at ten minute intervals. The eyes were then treated with epinephrine bitartrate drops at concentrations of free base epinephrine of 1.1%, 0.27%, 0.05%, 0.027%, 0.005% or 0.0005%. An additional group of rabbits received dexamethasone pretreatment only. Intraocular pressure (IOP) was measured for the next four hours. Enhanced lowering of intraocular pressure was observed with dexamethasone pretreatment. Rabbits receiving the smaller dose of epinephrine with dexamethasone had the largest decrease in IOP at 135 minutes after instillation of the epinephrine drops (0.005% epinephrine, mean difference +/- standard error of mean = 5.4 +/- 1.1 mmHg). Similarly, the duration of significant decrease of the IOP was prolonged in the groups receiving the lower concentrations of epinephrine (0.005% epinephrine, 255 minutes after administration of epinephrine). The synergism between glucocorticoids and adrenergic agonists in lowering IOP may be potentially useful in the therapy of ocular hypertension and glaucoma.