Reduction of sodium dependent stump currents disturbs urodele limb regeneration

We have asked the question whether the natural electric currents which leave urodele limb stumps are in any way needed for their regeneration. As an initial test, we have greatly reduced such currents in the tiger salamander, Ambystoma tigrinum, by applying 0.5 mM amiloride to the stump skin or by immersion of the animals in sodium depleted media. We have also reduced such currents in the red spotted newt, Notophthalmus viridescens, by such immersion. Limb regeneration in half of the amiloride-treated animals was either entirely blocked or grossly deficient, while the others regenerated normally. Limb regeneration in sodium depleted media was consistently inhibited for some weeks but then recovered. These results are consistent with the hypothesis that stump currents are in some way needed for normal regeneration.