Change of calcium and cAMP concentration by adrenoceptor agents in cultured porcine corneal endothelial cells

It has been reported that beta-adrenergic receptors are localized in the co rneal endothelial cells. In this study, the change of cellular signal trans duction, such as intracellular calcium and cAMP, was determined with pure a drenergic agonists and commercial antiglaucoma adrenergic agents. The intra cellular calcium of cultured porcine corneal endothelial cells was inhibite d by 10 mu M isoproterenol and norepinephrine, but enhanced by propranolol and 50 mM KCl. In the case of phenylephrine, calcium mobility did not alter significantly. Verapamil, at 10 mu M, decreased intracellular calcium conc entration. In the presence of isoproterenol, cellular cAMP concentration in creased from 28.8 pmole/mg protein (1 mu M) to 42.2 pmole/mg protein (100 m u M) compared with control of 6.07 pmole/mg protein. Incubation with commer cial adrenergic eye drops, such as betaxolol, caused the cAMP concentration to increase from 21.6 pmole/mg protein (0.0005%) to 39.1 pmole/mg protein (0.05%). Adding commercial levobunolol and timolol into cells caused cellul ar cAMP to increase from 14.3 pmole/mg protein (0.0005%) to 840.5 pmole/mg protein (0.05%) and from 115.2 pmole/mg protein (0.00025%) to 931.0 pmoie/m g protein (0.025%), respectively. However, the preservative, benzalkonium c hloride, increased cellular cAMP from 15.4 pmole/mg protein (0.00001 mg/ml) to 1087.4 pmole/mg protein (0.01 mg/ml). It is concluded that the intracel lular calcium of corneal endothelium decreases when the cellular adrenergic receptor is activated by agonists. Benzalkonium chloride, due to its prese rvative in commercial antiglaucoma agents which increases cellular cAMP, ma y alter corneal endothelial physiology through long-term use.