Protein release from the internal surface of the squid giant axon membrane during excitation and potassium depolarization

The proteins in the perfusate collected from intracellularly perfused squid giant axons were analyzed after being labeled with radioactive ¹²⁵I-labeled Bolton-Hunter reagent. The rate of protein release into the perfusate was found to be increased by the following electrophysiological manipulations of the axons: (1) repetitive electrical stimulation at 60 Hz in axons perfused with normal potassium fluoride-containing solution or at 0.125 Hz in axons perfused with tetraethylammonium containing solution, (2) perfusion with 4-amino-pyridine solution which induces spontaneous electrical activity in the axon, and (3) depolarization of the axon induced by raising the external potassium concentration. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of the proteins released under these conditions yielded molecular weight profiles different from those of the extruded axoplasmic proteins. These observations indicate that there exists, in close association with the axonal membrane, a particular group of proteins, the solubility of which is readily affected by changes in the state of the membrane.