Abstract
The membrane site responsible for anomalous rectification was determined in frog sartorius muscle fibers. The total currentvoltage relation of glycerol-treated fibers which represents mainly the properties of the sarcolemma was linear for membrane potentials between about-90 and-50mV. Thus moderate depolarization-induced anomalous rectification in intact fibers represents a property of the sarcotubular system. The absence of slow hyperpolarization in glyceroltreated fibers was caused by the abolition of early conductance increase, and the sarcotubular system is responsible for the inward rectifier. Picrotoxin selectively inhibited both moderate depolarization-induced anomalous rectification and hyperpolarization-induced early conductance increase. This suggests that the same component in the sarcotubular system is responsible for these conductance changes. The inhibition with picrotoxin of moderate depolarization-induced anomalous rectification suggests the possibility that it is caused by an electrogenic effect rather than a decrease in K conductance. A sarcolemmal hyperpolarization-activated slow conductance increase was revealed.
