Enhancing molecular flux through nanopores by means of attractive interactions.

Abstract

The classic experiments by Galvani and colleagues (as discussed by Piccolino in ref. 1) in the 1790s led him to suggest that neural conduction and muscle contraction are governed by a form of electricity. Nearly 100 years later, Santiago Ramon y Cajal’s (2) use of Golgi stains provided stunning images of the complex neural architecture, and hinted at how signals might be propagated along relatively vast distances within the body. In the mid-20th century, electrophysiological experiments on giant squid axons by Hodgkin and Huxley (3) 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 nerve cell membranes (3–6). By computing the energy for transporting ions across an ultrathin cell membrane (≈4 nm thick) that has a low dielectric constant (e ∼ 2), it was shown that ion-selective transporters, now known as protein ion channels, are water-filled pores (7). The ability to observe single molecules of excitatory material in artificial cell membranes (8–10) and in frog muscle fibers (11, 12) provided keen insight into 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 (13), gene transduction between bacteria, and the transfer of genetic information from some viruses and bacteriophages to cells (14). The theoretical work by Bauer and Nadler (15) in this issue of …