A steady efflux of ionic current predicts hind limb development in the axolotl

Abstract

For more than a week prior to the emergence of a hind limb, a steady electric current is driven out of the ventrolateral flank in the immature axolotl, returning through the integument in adjacent regions of the body. A marked peak in the density of this outcurrent could be observed over the exact area of hind limb formation 4 to 6 days prior to its appearance. After a bud projected from the flank, current densities were observed to decrease in magnitude yet localize about the early limb. In about one-half of the animals observed, current reversed its polarity and entered the apex of large buds, 0.4 to 0.5 mm in length. We discuss the possible role such endogenous currents and their associated fields may play in limb development and compare it to similar current flow associated with the regeneration of amphibian limbs.

Controlling Cell Behavior Electrically: Current Views and Future Potential

“…Importantly, physiological EFs establish chemical gradients in vivo. Current exits the prelimb bud region of amphibian embryos and precedes and predicts the point of emergence of the limb bud by several days (1,25,170). Injecting fluorescently labeled charged bovine serum albumin into the prelimb bud region, where the flow of current establishes a steady EF of up to 40 mV/mm (173), resulted not in symmetrical diffusion, but in a comet tail-like distribution of the fluorescent probe driven by electrophoresis within the extracellular space (138).…”

“…The TEP becomes short-circuited only at these sites from which currents of 1-10 A/cm 2 leave the flank. These "prophetic" currents precede limb bud emergence by several days and predict the sites from which limb buds will appear in amphibians, chicks, and mice (1,21,25,170).…”

Electrical dimensions in cell science

“…During limb development in amphibian embryos, ionic current flows out of the precise site on the flank skin at which the limb bud appears a day or so later (Borgens et al, 1983;Robinson, 1983). This predictive current also appears in chick and mouse, and reversing it in chick causes major limb abnormalities, indicating that it is required in limb development (Altizer et al, 2001).…”

Electrical fields, nerve growth and nerve regeneration

“…This current is carried predominantly by Na+, the transport of which sustains the potential difference across the embryonic epithelium (McCaig & Robinson, 1982). In both developing Xenopus and axolotl, localized, steady, endogenous current leaves the embryo at a location predictive of the future site of limb bud development, but the ions involved have not been identified (Robinson, 1983;Borgens, Rouleau & DeLanney, 1983). Currents of around 20 and 100 1aA/cm2, respectively, leave the primitive streak region in developing chick and mouse embryos (Jaffe & Stern, 1979;Winkel & Nuccitelli, 1989 (Robinson, 1985).…”