Stump currents in regenerating salamanders and newts.

We report here that a variety of salamanders and newts from differing habitats all drive a steady ionic electric current out of the forelimb stump tip after forelimb amputation. Several hours after amputation the density of this stump current ranges from about 10 to 100 microA/cm2 in most species, and declines with time. In most cases, the magnitude of the stump current is dependent on the concentration of Na+ in the external medium (an artificial pondwater), suggesting that the well-known Na+ -dependent transcutaneous voltage described in amphibia (particularly frogs) is the EMF for this stump current. These measurements add to those previously reported for the North American red spotted newt (Notophthalmus viridescens), and suggest that electrical changes following amputation of urodele limbs are widespread among members of this group.