The Transhyphal Electrical Current of Neuruspua crassa is Carried Principally by Protons

SUMMARY: During apical extension an ion current of about 0.2 μA cm−2 flows into the hyphal tips of Neurospora crassa and out from the distal regions of the hyphae. This current is carried principally by protons and requires phosphate and glucose in the growth medium. Exogenous calcium ions were required for tip extension but not for the current. A permeable pH sensitive dye, bromocresol green, provided evidence that the cytoplasm at sites of proton current entry was made acidic in comparison with the subapical cytoplasm. In a few cases non-growing hyphae were found with a normal current and growing hyphae were found with outward current at the apex. These current patterns, although rare, indicate there is no tight correlation between the vectorial flow of electrical current and hyphal extension in this organism.