Sodium Extrusion by Internally Dialyzed Squid Axons

Abstract

A method has been developed which allows a length of electrically excitable squid axon to be internally dialyzed against a continuously flowing solution of defined composition. Tests showed that diffusional exchange of small molecules in the axoplasm surrounding the dialysis tube occurred with a half-time of 2–5 min, and that protein does not cross the wall of the dialysis tube. The composition of the dialysis medium was (mM): K isethionate 151, K aspartate 151, taurine 275, MgCI₂ 4–10, NaCl 80, KCN 2, EDTA 0.1, ATP 5–10, and phosphoarginine 0–10. The following measurements were made: resting Na influx 57 pmole/cm²sec (n = 8); resting potassium efflux 59 pmole/ cm²sec (n = 4); stimulated Na efflux 3.1 pmole/cm²imp (n = 9); stimulated K efflux 2.9 pmole/cm²imp (n = 3); resting Na efflux 48 pmole/cm²sec (n = 18); Q₁₀ Na efflux 2.2 (n = 5). Removal of ATP and phosphoarginine from the dialysis medium (n = 4) or external application of strophanthidin (n = 1) reversibly reduced Na efflux to 10–13 pmole/cm²sec. A general conclusion from the study is that dialyzed squid axons have relatively normal passive permeability properties and that a substantial fraction of the Na efflux is under metabolic control although the Na extrusion mechanism may not be working perfectly.