Arginine-specific reagents remove sodium channel inactivation

Abstract

PROTEINS are often suggested to be the molecular components of excitable membranes which confer voltage-dependent permeability properties on nerve and muscle cells. Because of the relatively low concentration of the protein molecules directly responsible for ionic conductances compared with other membrane components, the isolation, characterisation, and reconstitution of these proteins is still at a rather early stage. Certain aspects of the molecular nature of the conductance mechanisms of excitable tissues, however, can be deduced using chemical reagents which specifically modify protein molecules. In particular, the sodium inactivation process can be eliminated by treatment with various proteolytic enzymes^1–3,6. Of these, trypsin is probably the most selective, cleaving mainly at arginyl or lysyl residues⁴. Several investigators have suggested that just such an exposed positively charged residue might be responsible for blocking the sodium conductance pathway to produce inactivation^5,6. Therefore, it should be possible to alter or remove inactivation by changing the configuration and/or charge of the blocking residue with a reagent specific for the residue involved. Glyoxal, phenylglyoxal and condensed 2,3-butanedione are three such reagents which are very reactive with the guanidino group of arginine^7–9. This paper describes the effect on sodium inactivation of these agents when they are internally perfused in the squid axon.