Galvanotaxis

Verworn, in 1899, wrote that Kühne observed in 1864 that Actinosphaerium followed a very different law of excitation. The finding stayed isolated and unnoticed for more than two decades.¹ It was recalled only after other effects of the galvanic current, which made up galvanotaxis, were discovered. A long series of free-living cells was then examined. Verworn said all of them followed a law of polar excitation that differed in several ways from that of nerve and muscle.¹ Loeb described the plain laboratory result in 1912. Animals placed in a trough with a current through the water orient to its direction and move toward the positive or the negative pole.³

Loeb gave a physical account. Where current curves enter cells, ions collect and alter the chemical reactions. Current lines therefore play the part that light rays play in heliotropism.³ He added that light acts on the free surface of the animal, while current affects all cells and nerves. He used this to explain why fewer species show typical galvanotropism than show heliotropism.³ In 1916 he described the shrimp Palaemonetes, which is compelled toward the anode in dilute salt solution and can walk forwards, backwards or sideways.⁵ He also called galvanotropism purely a laboratory product, since almost no animal meets an electric current outside experiments, yet the reaction is common.⁴

Lillie, in 1923, listed electrotonus, polar disintegration of cells, galvanotropic growth and galvanotaxis as processes showing polar action. In all of them the direction of the current relative to the cell surface decides the physiological effect.⁶ He compared this to electrolysis at an electrode, where the effect depends on whether current passes from metal to solution or the reverse.⁶ Driesch, in 1908, took a narrower view of taxis in general. Experiments in the style of Jennings had shown that chemicals, heat, light and contact do not produce taxis. He named galvanotaxis as the exception and expected the range of taxis to prove very restricted.²

Funk, in 2015, reviewed in vitro work in which many cell types migrate to the cathode in applied fields of about 0.1 to 10 V/cm. Examples include neural crest cells, fibroblasts and keratinocytes.⁷ Fewer types, such as corneal endothelial cells and human granulocytes, move to the anode. Both speed and direction depend on voltage.⁷ Sun, in 2017, reviewed microfluidic chambers and described work by Djamgoz and colleagues. Highly metastatic rat prostate cancer MAT-LyLu cells moved to the cathode, while weakly metastatic AT-2 cells did not respond.⁸ Sheth and Esfandiari, in 2022, reported that metastatic sublines of 4T1 differed in threshold. The parental and lung lines responded at 50 mV/mm, while others moved to the anode at 100 mV/mm or higher.⁹