Concentration gradient of Na + and K + ions in outer segments of retinal rods.

Abstract

The localization of the NA+ ion in the outer segments of frog retinal rods and the state (free or bound) of NA+ and K+ ions in isolated outer segments of bovine rods were studied. The Na+ ion localized mainly in discs of the outer segments; interdisc spaces, continuations of the cell cytoplasm, were rich in K+. About 80% of Na+ and K+ ions in the outer segments are in a relatively free state. Phospholipids of the segment membranes are bound mainly with Na+. The concentration gradient of the cations between contents of the discs (high Na+, low K+) and interdisc spaces (high K+, low Na+) was calculated approximately from the content, distribution, and state of Na+ and K+ in native outer segments which can be regarded as a battery of extracellular compartments separated by intracellular contents. If isolated segments are incubated in media differing in Na+ and K+ content, the accumulation of these cations is limited although dependent on their concentration in the incubation medium.