The membranes of most excitable cells contain a distinct set of potassium channels that rapidly open and close following depolarization, giving rise to a transient outward membrane current (IA). This current seems to play an important role in allowing neurons to encode graded depolarization into spike train information; in action potential repolarization, particularly in cardiac muscle cells; and in several aspects of synaptic transmission. As a modifier of the responsiveness of postsynaptic neurons to synaptic potentials,IA is a critical determinant of the integrative behavior of certain neural networks. Recent studies indicate that IA can be physiologically modulated by synaptic influences and during learning. The discovery of Drosophila mutants where IA is defective or absent provides the hope that this may soon be the first potassium channel amenable to structural analysis by molecular genetic techniques.
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