Rolando Guidelli
Professor
Title: What Ion Flow Along Ion Channels Can Tell About Their Functional Activity
Biography
Biography: Rolando Guidelli
Abstract
The most direct method for verifying the functional activity of channel-forming peptides and proteins consists in monitoring the flow of physiologically relevant inorganic ions, such as Na+, K+ and Cl–, along the ion channels. Measurements of average and single channel currents across bilayer lipid membranes (BLMs) interposed between two aqueous solutions are extensively employed to this end. A major drawback of BLMs is their fragility, high sensitivity toward vibrations and mechanical shocks, and low resistance to electric fields. To overcome this problem, metal-supported tethered BLMs (tBLMs) have been devised, where the BLM is anchored to the metal via a hydrophilic spacer that replaces the water phase on the metal side. However, only mercury-supported tBLMs can measure and regulate the flow of the above inorganic ions, thanks to mercury liquid state and high hydrogen overpotential. Thus, they react to the presence of proteins, charges and physical forces in a dynamic and responsive manner, by reorganizing upon interaction with external perturbations and mimicking the functionality of living cell membranes. The potential of Hg-supported tBLMs is illustrated by the use of different electrochemical techniques. Moreover, a tBLM formed on a mercury cap electrodeposited on a platinum microdisk yields a micro tBLM that maintains the same fluidity and lipid lateral mobility as on a hanging mercury drop and allows the recording of single channel currents and of two-photon fluorescence lifetime images of lipid rafts and gel-phase microdomains, opening the way to its use in high throughput screening applications.