Na+–Li+ Exchange in Single Muscle Fibers of the Giant Barnacle

Abstract

The net efflux of Na+ was measured in single muscle fibers of the giant barnacle, Balanus nubilus, bathed in Li+-Ringer solution. These experiments indicate one-to-one exchange of Li+ for Na+. This exchange occurs in two phases: a rapid exchange fraction complete within 1 h, and a slow exchange incomplete after 8 h. Intracellular Na+ activity, (aNa)i, decreased more slowly than total fiber Na+ concentration after immersion of the fibers in Li+-Ringer. The implications of this result regarding intracellular Na+ compartmentalization are discussed.