“…For [Zn2+]o between 0.1 and !.0 raM, the action potential duration continues to increase (Mashima & Washio, 1964;Taylor, Preiser & Sandow, 1972), the maximum rate of depolarization and overshoot are reduced (Taylor et al, 1972;Sandow & Pagala, 1978), and there is a decrease in membrane chloride conductance with little change in the resting potassium conductance (Mashima & Washio, 1964;Hutter & Warner, 1967b;Stanfield, 1970). The resting membrane potassium conductance in frog skeletal muscle fibers is generally ascribed to the inward potassium rectifier (Katz, 1949;Hodgkin & Horowicz, 1959;Adrian & Freygang, 1962).…”