DESCRIPTION: The broad, long-term objectives of this proposal are to characterize the structure-function relationship of the parts of sodium channels that control slow inactivation and its interactions with other channel functions, and to ultimately define how abnormalities in channel structure might lead to disease states like epilepsy and the periodic paralyses. The specific aims are: 1) to make, express and compare wildtype and mutant sodium channels to determine which part of the channel molecule controls slow activation; and 2) to determine the nature of interaction between slow inactivation and activation. The health-relatedness of this proposal is in its application to neuronal excitability. One critical factor in neuronal hyperexcitability (that could lead to epilepsy and other diseases involving loss of control over cell excitability) is a depolarization in the midpoint and increase in slope of the F(Vh) curve which leads to an increase in the number of channels available for activation from resting potential. Macroscopic sodium currents and single channel currents will be recorded from Xenopus oocytes expressing wild-type and mutant sodium channels using the patch clamp technique. Slow inactivation properties, including valence and midpoint of the F(Vh) curve as well as slow inactivation onset and recovery rates will be compared between wildtype and sodium channel mutants. Activation voltage dependence and kinetics, fast inactivation kinetics and channel permeation properties will also be monitored to assess other potential ramifications of introduced mutations.