The effects of digitalis-like compounds on rat lenses

PURPOSE. Fundamental to the maintenance of ionic concentration gradients an d transparency of the lens is the activity of Na+,K+-adenosine triphosphata se (ATPase) in the epithelial layer. Recent studies have identified endogen ous digitalis-like compounds (DLCs) and 19-norbufalin and its peptide deriv atives in human cataractous lenses. These compounds inhibit the activity of Na+,K+- ATPase and have been suggested to be involved in cataract formatio n. The present experiments were designed to test this hypothesis by determi ning the ability of digitalis and DLCs to induce changes in protein composi tion and leakage from rat lenses in organ culture. METHODS. DLCs were determined in rat lenses using three independent assays: interaction with ouabain antibodies, interaction with bufalin antibodies, and inhibition of [H-3]-ouabain binding to red blood cells. Rat lenses were incubated in modified TC-199 medium in 5% CO2 atmosphere at 37 degrees C f or the time of the experiment. The onset of cataractogenesis was assessed b y measuring protein leakage from Lenses and by crystallin composition in th e lens and media. RESULTS. DLCs were present in rat lens with concentrations:to 30 times high er in the capsular-epithelial layer than in the lens fibers regions. Ouabai n, bufalin. digoxin, and DLC induced dose- and time-dependent leakage of pr otein from rat lenses. Lenses incubated with these compounds showed alterat ions in crystallin content consistent with changes that initiate opacity. h ll the compounds caused a multilayrering of epithelial cells in the region surrounding the mitotic area and, at the same time, cell death in the centr al anterior region. CONCLUSIONS. Digitalis and endogenous DLCs are cataractogenic factors. Thes e results, together with the demonstration of DLCs in the normal lens and t heir increased levels in human cataractous lenses, strongly suggest their i nvolvement in the molecular mechanisms responsible for cataract formation.