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

Abstract

Electrical currents near regenerating newt limbs were measured with a recently developed vibrating probe.Steady currents with local surface densities of 10 to 100 MA/cm2 or more leave the end of the stump during the first 5-10 days after amputation and are balanced by currents with densities of only 1-3 jA/cm2 that enter the intact skin around the stump. They are immediately dependent upn the entry of sodium ions 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. We have recently demonstrated that anuran limb regeneration can be initiated by driving a small steady current through the stump. The effective stimulus is truly electrical (i.e., the effect is not mediated by electrode products). Current must be pulled out of the stump to induce regeneration, whereas inward current actually induces degeneration (1). Many other stimuli are known to induce a measure of regeneration in adult anurans (2, 3). The critical question is whether a comparable electrical component is part of a natural control system. As a first step in answering this question, we ask whether normally regenerating amphibian stumps generate comparable currents after amputation.An old and nearly forgotten paper of Monroy's indicates that endogenous currents do, indeed, leave the regenerating amphibian stump surface (4). Monroy used a relatively low-resistance galvanometer to make these measurements. Hence, as will be discussed below, it is possible to estimate the size of these currents. Two subsequent studies have yielded somewhat contradictory results (5-7). However, both Becker and the Roses used instruments with very high resistance, so the resistance between the points of measurement was essentially the resistance along the skin surface. Because this was not measured, the size of the currents responsible for the measured voltages cannot be inferred.We have therefore reinvestigated the stump currents in amputated and regenerating newt limbs, using the recently developed ultrasensitive vibrating probe (8). With it, one can directly measure the pattern of current densities entering or leaving a biological source immersed in its natural aqueous medium. Furthermore, the probe is placed at a sufficient distance from the animal as to practically avoid disturbing it. The probe is vibrated between two external points and registers the minute voltage difference generated by any current that may travel between these two points. The only accessory measurement needed to infer the current density is the resistivity of the medium. Use of the vibrating probe allows one to measure exThe costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertis...

Transcriptomic, proteomic, and metabolomic landscape of positional memory in the caudal fin of zebrafish

“…Patterning and size control during development and regeneration are also regulated by bioelectric signaling (52,(71)(72)(73)(74)(75)(76)(77)(78). Mutations in two strains of zebrafish with fin size phenotypes map to genes involved in bioelectric signaling (41,79).…”

Looking proximally and distally: 100 years of limb regeneration and beyond

“…Na þ influx in the amputated newt limb and H þ efflux in the amputated tail of Xenopus tadpoles generate ionic currents across the wound epidermis essential for regeneration. Na þ influx is via sodium channels (Borgens et al, 1977). H þ efflux in the amputated tail is driven by a plasma membrane ATPase in the epidermal cells , and is likely to be important for limb regeneration as well, given that a gene encoding a v-ATPase was the most abundant clone in a suppressive subtraction cDNA library made from dedifferentiating axolotl limb tissue (Gorsic et al, 2008).…”

Beyond early development: Xenopus as an emerging model for the study of regenerative mechanisms

“…It is well documented that endogenous electric fields play a role in regeneration, and it has been shown that applied electric fields are able to enhance regeneration and repair in vertebrates (Borgens et al, 1977(Borgens et al, , 1981Kerns and Lucchinetti, 1992;McCaig et al, 2005). have recently demonstrated a molecular link between electric currents and tail regeneration in Xenopus.…”