Modulation of the Potassium Conductance in the Squid Giant Axon
The potassium conductance of the squid giant axon is considered the classical example of the delayed rectifier-type of voltage dependent potassium permeability (Hodgkin and Huxley, 1952). In this preparation a large number of experiments have been done on K ionic currents using intact axons and under conditions of internal perfusion to study the selectivity and voltage dependence of the conductance. It has also been possible to record single channel events (Conti and Neher, 1980; Llano and Bezanilla, 1985; Llano, Webb and Bezanilla, 1987) and gating currents related to the movement of the charge responsible for the opening and closing of the K conductance (White and Bezanilla, 1985). The squid giant axon is then an ideal preparation for a detailed analysis of K channel gating because all types of electrophysiological recordings can be made in the same preparation, an important prerequisite for formulating a complete model of channel gating. We review here evidence that the K conductance in the squid axon is modulated by ATP-dependent phosphorylation. The changes induced by ATP in the macroscopic currents appear to be the result of a combined effect on more than one type of K channel. We also provide evidence for a Ca-activated component of the K conductance.
KeywordsPermeability Hydrolysis Magnesium Fluoride Adenosine
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