Electrophysiological effects of corticosteroids on the retinal pigment epithelium

As corticosteroids appear to intervene in pathogenesis of central serous chorioretinopathy, ion transport changes within the retinal pigment epithelium (RPE) might be involved. Electrophysiological responses to corticosteroid administration were recorded in vivo and in vitro.

Clinical study: The standing ocular potential was recorded during intravenous (IV) infusion of glucose 5% and glucose 5% + prednisolone 0.2% in 14 patients with relapsing multiple sclerosis. The results were compared with a control group receiving two successive identical glucose 5% infusions. In vitro study: Native tissue explants (RPE + choroid, porcine, and bovine) were placed in a Ussing-type chamber. After baseline determination of the transepithelial potential (PD), short circuit current (I(sc)) and transepithelial resistance (R(t)), the effect of apical hydrocortisone (HC) 10(-4) M was determined.

Clinical study: A significant rise of the standing potential was found after glucose infusion (P = 0.005), whereas no change was detected after IV glucose + prednisolone (P = 0.695). In vitro study: In the porcine RPE, the mean baseline PD and I(sc) were significantly reduced (both P: = 0.012) after applying apical 10(-4) HC. R(t) was also significantly reduced (P = 0.01). The same type of response, observed in bovine RPE, was reduced in low chloride/low bicarbonate conditions.

Corticosteroids modified electrophysiological parameters representing RPE function in vivo. The existence of an RPE-specific effect was confirmed in vitro. Further work is required to link the observed ion transport changes to a reduction of apical, subretinal fluid absorption.