MULTIPLE GATING MODES AND THE EFFECT OF MODULATING FACTORS ON THE MU-I SODIUM-CHANNEL

Macroscopic current from the mu-l skeletal muscle sodium channel expressed in Xenopus oocytes shows inactivation with two exponential components. The major, slower component's amplitude decreases with rapid pulsing. When mu-l cRNA is coinjected with rat skeletal muscle or brain mRNA the faster component becomes predominant. Individual mu-l channels switch between two principal gating modes, opening either only once per depolarization, or repeatedly in long bursts. These two modes differ in both activation and inactivation kinetics. There is also evidence for additional gating modes. It appears that the equilibrium among gating modes is influenced by a modulating factor encoded in rat skeletal muscle and brain mRNA. The modal gating is similar to that observed in hyperkalemic periodic paralysis.