The effects of electrical fields on wound healing and directed neurite growth in Xenopus laevis

Ann Marie Rajnicek, Purdue University

Abstract

Healing of Xenopus neurulae was studied to investigate the role of endogenous sodium-carried electric currents in wound closure. Transected embryos healed completely within 7 hours in an artificial pond water medium. Wound closure was biphasic, with a rapid purse string-like contraction, which was independent of sodium concentration, followed by a slower, sodium-dependent phase. The initial contraction was reversibly inhibited by cytochalasin B. Healing was prevented when neurulae were wounded and left to heal in sodium-free medium. Healing was also prevented in the presence of amiloride, benzamil or ouabain, drugs that inhibit sodium flux through the epithelium. The transepithelial potential measured in intact neurulae fell rapidly and reversibly by 70% in response to 10 $\mu$M amiloride. Currents measured leaving the wound also decreased by 70% following amiloride addition. Healing of embryos in sodium-free medium was enhanced by application of current that mimicked the direction of the endogenous wound current. Aldosterone, which increases transepithelial sodium transport, augmented healing and increased the wound currents. The results indicate that at least one phase of wound healing in Xenopus neurulae is dependent upon an endogenous sodium-carried electric current. The current may act by guiding epithelial cells to the wound site. Endogenous electrical fields have been proposed as a guiding factor for developing neurites, based in large part on observations of isolated Xenopus neurons in vitro. These studies were limited to neurites growing on tissue culture plastic. In the present study, the contribution of the growth surface to field-induced responses was studied by growing Xenopus neurites on various surfaces and quantitating the response to electrical fields. Neurite distribution on the somas and overall growth for control cells were uniform on all substrates. Neurites extended predominantly from the cathode-facing halves of somas, regardless of the substrate. Neurite growth was biased toward the anode on Matrigel, polylysine and polylysine coated with laminin, and toward the cathode on Falcon and Plastek brand tissue culture plastics and laminin. The varied galvanotropic responses may be related directly to the growth surface or may result from selective differentiation of neuronal subpopulations or types of neurites which respond differently to fields. The substrate may select for the development of axons or dendrites, which then respond toward different electrodes.

Degree

Ph.D.

Advisors

Robinson, Purdue University.

Subject Area

Biology

COinS