Agonist-induced effects on cyclic AMP metabolism are affected in pigment epithelial cells of the Royal College of Surgeons rat.

Recent work has demonstrated that stimulation of cAMP production via A2-adenosine receptors is reduced in cultured retinal pigment epithelial cells from the RCS rat. Cultured rat RPE cells are also shown to possess beta 2-adrenergic receptors positively coupled to cAMP production. Isoproterenol and salbutamol both stimulate cAMP levels with half maximal (EC50) values of 0.5 and 0.2 microM, respectively. Isoproterenol action is attenuated most effectively by the beta 2-antagonist, ICI 118551, while the beta 1-antagonist, CGP 20712A, is only partially effective. Isoproterenol-stimulated cAMP production is markedly reduced in the RCS rat RPE when compared to control cultures. In passaged RCS rat RPE cells cAMP stimulation by 10 microM isoproterenol was 6.4% of that by control cultures and in primary cultures it was around 75% of controls. The observed EC50 values were 0.4 and 1.3 microM for passaged control and RCS rat RPE cells, respectively. Melatonin negatively influences cAMP production in the RPE via Gi-proteins. Melatonin attenuated the action of forskolin by 51.1% in control rat RPE but only by 18.6% in the RCS rat RPE. The dose-response curve for melatonin shows an approximate 1000-fold shift in potency in the RCS rat. bFGF also has an inhibitory effect on rat RPE cells. bFGF (50ng/ml) attenuated forskolin-stimulated cAMP levels by 61.9% in control rat RPE but had not effect on the action of forskolin in RCS rat RPE. Serotonin (100 microM) potentiates the forskolin-induced stimulation of cAMP by 140.1%. However, unlike isoproterenol, melatonin and bFGF, the action of serotonin on adenylate cyclase appears normal in the RCS rat RPE. We conclude that the defect in the RCS rat RPE is likely to be due to impaired coupling of the components of the adenylate cyclase system and that this is most probably an abnormal interaction of adenylate cyclase with G-protein alpha-subunits.