Purpose: To investigate whether antibodies against a 100 kDa protein purified by furosemide affinity chromatography from Ehrlich ascites tumour cells could inhibit Na+, K+, Cl- co-transport in the isolated frog retinal pigment epithelium. Methods: The rate of Na+, K+, Cl- co-transport across the retinal membrane in the isolated frog RPE preparation was measured as the rate of decrease in the intracellular Cl- activity observed after administration of furosemide in the apical bath. The intracellular CI-activity was measured with double barrelled Cl- sensitive microelectrodes. Results: Incubation of frog retinal pigment epithelium for 30 min with antibodies reduced the rate of Na+, K+, Cl- co-transport by 43%, while leaving all other measured electrophysiological parameters intact. Conclusion: The antibodies inhibit Na+, K+, Cl- co-transport in the frog retinal pigment epithelium, This could be due to binding of the antibodies to the cotransporter itself or to a regulatory protein.
