Kinetic studies at the inner pore of the sodium channel

Voltage-gated Na+ channels are pore forming, ion conducting macromolecules which are located in the cell membrane and have a central role in physiology: they enable transmission of electrical signals between cells and are therefore essential for physiological processes like the beating of the heart, skeletal muscle motion, and signal transduction in the nervous system. The proper function of Na+ channels requires coordinated gating, i.e. the proper opening and closing of their ion-permeable pores. Apart from opening and closing, channels can transit through periodic episodes of inexcitability called "inactivation". "Inactivation" is of superior physiological importance because it is a major determinant of signal processing in the nervous system and of the coordinated function of skeletal muscle and the heart. Accordingly, impaired inactivation of Na+ channels is responsible for a number of diseases like certain forms of epilepsy, skeletal muscle dysfunction, and irregular beating of the heart (arrhythmias). Na+ channels may enter several types of inactivated states, which are classified with regard to their time course of development and removal. Whereas "fast inactivation" is characterized by time constants of development and removal on the order of several milliseconds, slower inactivated states exhibit time constants of up to several minutes. Fast inactivation is known to occur by a block of the inner vestibule of the channel by a molecular lid. The molecular basis of slower inactivated states, however, remains obscure. We have recently suggested that a very slow inactivation process, called ultra-slow inactivation, may be associated with a molecular rearrangement of the inner vestibule of the channel. The inner vestibule of the voltage-gated Na+ channel is considered to be lined by specific parts of the molecule called S6 segments. The aim of the project is to elucidate the role of a specific S6 segment, S6 of domain IV (DIV-S6), in the process of ultra-slow inactivation. DIV-S6 has a pivotal role in the modulation of Na channel gating and it is known to contain the binding sites for drugs used in the treatment of cardiac arrhythmias, epilepsy and pain. We will introduce mutations into DIV-S6 and test the effect of these mutations on ultra-slow inactivation and on the modulation of ultra-slow inactivation by specific drugs. The results of the submitted project will improve our understanding of the role of DIV-S6 in channel gating and in the mechanism of action of ion channel modulating drugs.

Voltage-gated Na+ channels are pore forming, ion conducting macromolecules which are located in the cell membrane and have a central role in physiology: they enable transmission of electrical signals between cells and are therefore essential for physiological processes like the beating of the heart, skeletal muscle motion, and signal transduction in the nervous system. The proper function of Na+ channels requires coordinated gating, i.e. the proper opening and closing of their ion-permeable pores. Apart from opening and closing, channels can transit through periodic episodes of inexcitability called "inactivation". "Inactivation" is of superior physiological importance because it is a major determinant of signal processing in the nervous system and of the coordinated function of skeletal muscle and the heart. Accordingly, impaired inactivation of Na+ channels is responsible for a number of diseases like certain forms of epilepsy, skeletal muscle dysfunction, and irregular beating of the heart (arrhythmias). Na+ channels may enter several types of inactivated states, which are classified with regard to their time course of development and removal. Whereas "fast inactivation" is characterized by time constants of development and removal on the order of several milliseconds, slower inactivated states exhibit time constants of up to several minutes. Fast inactivation is known to occur by a block of the inner vestibule of the channel by a molecular lid. The molecular basis of slower inactivated states, however, remains obscure. We have recently suggested that a very slow inactivation process, called ultra-slow inactivation, may be associated with a molecular rearrangement of the inner vestibule of the channel. The inner vestibule of the voltage-gated Na+ channel is considered to be lined by specific parts of the molecule called S6 segments. The aim of the project is to elucidate the role of a specific S6 segment, S6 of domain IV (DIV-S6), in the process of ultra-slow inactivation. DIV-S6 has a pivotal role in the modulation of Na channel gating and it is known to contain the binding sites for drugs used in the treatment of cardiac arrhythmias, epilepsy and pain. We will introduce mutations into DIV-S6 and test the effect of these mutations on ultra-slow inactivation and on the modulation of ultra-slow inactivation by specific drugs. The results of the submitted project will improve our understanding of the role of DIV-S6 in channel gating and in the mechanism of action of ion channel modulating drugs.