Transmembrane macromolecule rotation model--molecular hypothesis of membrane excitation

A hypothesis concerning the molecular changes in the nerve cell membrane during excitation is presented. Based upon established principles about the interaction of hydrophobic and hydrophilic ligands and upon recent facts concerning the contraction of neurofilaments, the hypothesis accounts for both the initiation of the action potential and its conduction along the nerve axon without attenuation. The hypothesis can be summarized as follows: When acetylcholine combines with the acetylcholine receptor (AchR) alpha subunit, hydrophobic subsites are exposed at the bound surface of AchR. Since hydrophobic portions are quite unstable, the subsites move to the center of the membrane, which is hydrophobic. It is postulated that the rotation of receptor subunits makes the center an ion channel. Ca++ flowing in through the ion channel causes the undercoating filaments to contract and this contraction results in the conduction of an action potential along the axon. The contraction of the undercoating filaments induces transmembrane rotation of globular protein connected to the filaments. At right angles to the axon the force of the hydrophobic bond between membrane macromolecules is so strong that many cylindrical lipid structures are formed. The gaps between the rotatory cylinders serve as ion channels. Ca++ passing through the ion channels allows for the conduction of an action potential without attenuation.