The role of Na+ ions in the transport of alpha-aminoisobutyric acid and other amino acids into the lens.

The transport systems for a-AIB and neutral, acid, and basic amino acids into lens were found to comprise a ~N a*-dependent and a Na-independent component. Na ions, required for 60 to 70 per cent of C-a-AlB transported into rabbit lens, were combined with a-AIB molecules in a 1:1 ratio while transported by a common "carrier" system. However, Na ions did not affect the diffusion constant nor the C-a-AIB efflux rates from the lens. The in vitro lens incubations showed accumulation by the lens and against the concentration gradient of >C-aAIB and other >C-amino acids. Throughout the incubation periods, Na ions transported with the aynino acid continued to be actively extruded from the lens. The Na+ deprivation effects closely resembled ouabain inhibitory effects on a-AIB transport, and were both exerted in the lens epithelium. These remits, and the independence of the lens a-AIB and K or Rb carriers, established the presence of a Na ions link between the IS!a*-dependent fraction of a-AIB and other amino acid transport systems and the ouabain-sensitive Na+-K "pump."