Related Experiment Videos
Modification by timolol of catecholamine stimulation of chloride transport in isolated corneas
Abstract:
In the isolated frog cornea, 10(-5)M timolol completely blocked the stimulation of chloride transport by 10(-6)M isoproterenol. In this preraration, timolol inconsistently modified the response to epinephrine. In some experiments, epinephrine added to the bathing medium after timolol caused a smaller than normal increase in chloride transport, but in other instances, epinephrine caused a decrease in chloride transport. In the isolated rabbit cornea, 10(-5)M timolol totally blocked the stimulation of chloride transport by 10(-6)M epinephrine. In vivo, topical treatment of rabbit eyes with 0.5% timolol resulted in corneas from these eyes having an inhibited response to epinephrine when incubated in vitro. This inability to stimulate chloride transport persisted for several days following termination of topical treatment with timolol.
Insights
Timolol, a beta-blocker, effectively blocks isoproterenol and epinephrine-induced chloride transport in frog and rabbit corneas. This effect persists even after topical timolol treatment is discontinued.
Area of Science:
- Ophthalmology
- Pharmacology
- Corneal Physiology
Background:
- Beta-adrenergic agonists like isoproterenol and epinephrine stimulate chloride transport in the cornea.
- The role of beta-adrenergic receptors in regulating corneal ion transport is of significant interest.
Purpose of the Study:
- To investigate the effect of timolol, a non-selective beta-adrenergic antagonist, on corneal chloride transport.
- To determine if timolol blocks the stimulatory effects of beta-adrenergic agonists on corneal ion transport in different species.
Main Methods:
- Experiments were conducted on isolated frog and rabbit corneas.
- Chloride transport was measured in response to isoproterenol and epinephrine, with and without timolol.
- In vivo studies involved topical application of timolol to rabbit eyes, followed by in vitro assessment of corneal response to epinephrine.
Main Results:
- In frog cornea, timolol completely blocked isoproterenol-stimulated chloride transport.
- Timolol inconsistently affected epinephrine response in frog cornea but completely blocked it in rabbit cornea.
- Topical timolol treatment in rabbits led to a persistent inhibition of epinephrine-stimulated chloride transport in vitro.
Conclusions:
- Timolol effectively antagonizes beta-adrenergic stimulation of chloride transport in the cornea.
- The blocking effect of timolol on corneal chloride transport is demonstrated in both amphibian and mammalian models.
- Topical timolol administration results in a sustained impairment of the cornea's response to adrenergic stimulation.