The membranes of excitable cells contain proteins that give these cells their special character. These protiens (called Na and K channels) are responsible for the time- and voltage-dependent permeability changes to Na and K ions that underlie the action potential and are also the receptors for local anesthetics and other neuroactive drugs. It is the long-term goal of this project to develop a molecular-level picture of these proteins using both electrophysiological and biochemical techniques on squid giant axons. Three immediate aims can be identified: 1) the use of protein modification techniques to investigate the importance of specific amino acids in the K channel gating and permeation processes. These processes are most readily studied with macroscopic currents obtained using axial-wire voltage clamp techniques on squid giant axons. Because of some limitations of macroscopic ionic current measurements, potassium channel gating currents and single channel currents will also be studied. 2) The involvement of carboxyl groups near the inner surface of sodium pores in the permeation process of Na channels will be studied. 3) The present picture of the sodium channel inactivation process will be re-examined. Specifically, experiments will be designed to determine if inactivation has an intrinsic voltage-dependence or derives its voltage-dependence from precursor steps in the gating process. Also, an attempt will be made to restore inactivation in axons whose inactivation has been removed by proteolytic enzymes. A knowledge of the important chemical groups of these proteins and a detailed knowledge of the interactions of drugs with the proteins will ultimately be useful in understanding the properties of the porteins in pathological conditions and in designing new therapeutic agents wih fewer side effects.
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