FIG. 7.

Electrical responses of the wild type and the mid-1 mutant to hyperosmotic treatment. The mycelial colony was flooded with 3 ml of BS; after about 15 min, when hyphal tips at the colony edge had resumed growth, hyphal trunk cells about 200 to 500 μm behind the colony edge were impaled with double-barrel microelectrodes. When the membrane potential had stabilized (circles) (initial potential), 0.5 ml of BS plus 1,000 mM sucrose was added in a circle around the microscope objective. Arrival of the hyperosmotic solution at the hypha being measured was confirmed by the observation of a refractive wave. A transient depolarization (transient change) (always observed in the wild type) or hyperpolarization (occasionally observed in the mid-1 mutant [squares]) was observed within 2 min, followed by a long-term hyperpolarization (triangles) within 4 to 6 min. The transient and final changes respectively, are the transient potential or final potential minus the initial potential. Data are jittered on the x axis for clarity.