Bioelectricity and regeneration: large currents leave the stumps of regenerating newt limbs.

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Abstract
Electrical currents near regenerating newt [Notophthalmus viridescens] limbs were measured with a recently developed vibrating probe. Steady currents with local surface densities of 10-100 .mu.A/cm2 or more leave the end of the stump during the 1st 5-10 days after amputation and are balanced by currents with densities of only 1-3 .mu.A/cm2 that enter the intact skin around the stump. They are immediately dependent on the entry of Na+ into this skin and are therefore inferred to be skin-driven. The outward currents are comparable in direction, density, duration and position to artificially imposed currents previously found sufficient to induce significant regeneration of amputated adult frog limbs. This comparison suggests that the endogenous stump currents play some causal role in initiating regeneration.