Some observations on the behaviour of the sodium efflux in barnacle muscle fibres towards lithium ions

Abstract

1. 1. The behaviour of the Na efflux towards Li + was studied using single barnacle muscle fibres as a preparation. 2. 2. It is found that the Na efflux into Li +-ASW (artificial seawater) is reduced and that this effect is not fully reversed by returning back to Na +-ASW. 3. 3. Preinjection of 100 mM-EGTA reduces the magnitude of the fall of the Na efflux into Li +-ASW. 4. 4(a). The remaining Na efflux into Li +-ASW is further reduced by external application of 10 −4 M-ouabain. (b) The remaining Na efflux in ouabain-poisoned fibres is reduced by replacing Na e by Li +. However, some fibres show a rise rather than a fall. 5. 5. Fibres loaded with NaCl (by injection) show a prompt and sustained stimulation of the Na efflux when Na e is replaced by Li +. A similar but less pronounced response is often seen with ouabain-poisoned fibres. 6. 6. Injection of LiCl (e.g. a 2 M-solution), causes a 20% fall in Na efflux. Subsequent replacement of Na e by Li + fails to bring about a fall in the remaining efflux. 7. 7. Itis concluded that the Na efflux in these fibres consists of a Na-Na exchange diffusion component which is not mediated by the Na-K pump and that its operation is interrupted by injecting Li +. The relative size of this component is about one-fifth and not one-half of the Na efflux.