Metabolic studies on calcium transport in mammalian lens

Three important findings concerning the calcium pump in a mammalian lens are reported: 1) glycolysis is sufficient to support active transport of calcium in the young rabbit lens; 2) in addition to the epithelium posterior and anterior fibers are involved in calcium transport; 3) inhibition of glycolysis and the calcium pump result in calcium accumulation and subsequent opacification. That respiration does not contribute to the energy needs of the Ca++ pump is based on results which demonstrate that cyanide, dinitrophenol, and azide have no effect on 45Ca efflux when glucose is present. Moreover, incubation of lenses for 20 hrs. in the presence of cyanide fails to alter the internal concentration of calcium. The inhibition of glucose metabolism with iodoacetate (IAA) results in the accumulation of calcium to a level of 0.71mM and the formation of superficial subcapsular opacities. Evidence that fibers are also responsible for calcium extrusion consists of two findings: 1) removal of the epithelium from a lens results in calcium accumulation but the addition of IAA to such a lens results in a further gain in calcium; 2) the accumulation of 45Ca across the posterior surface of a lens partially immersed in medium is accelerated following inhibition of glycolysis.