Changes in intracellular pH accompanying chemoreception in the plasmodia of Physarum polycephalum

A new method for measuring intracellular pH, employing the intrinsic fluorescent pigments of the plasmodia of the myxomycete Physarum polycephalum, was used to study the role of pH in chemotactic transduction in the plasmodia. The cell became acidified following stimulation with the attractants alanine, glucose, galactose and maltose when their concentrations exceeded the respective thresholds of chemoreception and taxis. The degree of cell acidification paralleled the relaxing tendency in tension generation. A non-metabolizable attractant, 2-deoxyglucose, also acidified the cell. However, the repellent salts NaCl, KCl and CaCl2 did not change the intracellular pH. Our results suggest that the effects of attractants are mediated by intracellular pH, while the effects of repellents are transduced by ATP as reported previously.