The classic experiments by Galvani and his colleagues in the 1790s led him to suggest that neural conduction and muscle contraction are governed by a form of animal electricity. Nearly 100 years later, Santiago Ramon y Cajal?s use of Golgi stains provided stunning images of neural architecture complexity and a hint at how signals might be propagated along relatively vast distances within the body. In the mid 20th century, electrophysiology experiments on giant squid axons by Hodgkin and Huxley confirmed Galvani?s conjecture; the rapid transmission of information along nerve fibers is indeed electrical. Specifically, the propagation of the action potential in nerve is controlled by the spatial-temporal opening and closing of separate pathways for Na+ and K+ ions in those cell membranes (1,2). How these pathways switch or ?gate? between different conductance states (3,4) and selectively transport specific ions and molecules are still major areas of research. By computing the energy for transporting ions across an ultra-thin cell membrane (~ 4 nm thick) that has a low dielectric constant (' ~ 2), it was shown that ion-selective transporters, now known as protein ion channels, are water-filled pores (5). The ability to observe single molecules of excitatory material in artificial cell membranes (6-8) and in frog muscle fibers (9,10) provided the means to probe the structure-function relationship of ion channels. Channels, and channel-like entities also facilitate the transport of macromolecules in a wide variety of processes including protein translocation across membranes (11), gene transduction between bacteria, and the transfer of genetic information from some viruses and bacteriophage to cells (12). The theoretical work by Bauer and Nadler (13) described in this issue of PNAS brings us one step closer to understanding the mechanisms and advantages of molecular selectivity.
Citation: Proceedings of the National Academy of Sciences of the United States of America
Pub Type: Journals
anthrax, ion channels, selectivity