Dynamics of voltage-gated ion-channel proteins

The voltage dynamics in ensembles of a single type voltage-gated potassium-selective ion-channels is studied using the patch-clamp technique. A micron size, detached, patch of membrane, isolated from any intracellular effect, is embedded with a certain density of channels. Different patches of membrane, constructed with varied densities of channels, allow us to scan their number in the ensemble by more than three orders of magnitude. The input current to the membrane is served as a second control parameter. The transmembrane voltage exhibits distinct behavior in dense and dilute ensembles of channels. In dense ensembles, voltage fluctuations are constrained and exhibit relaxed oscillatory behavior typical to a simple two-state system. The detailed analysis presents the voltage fluctuations as a damped harmonic oscillator, driven by a noise term due to channel’s conduction fluctuations between closed (non-conducting) and open (conducting) states. At the other extreme of dilute ensembles, the voltage fluctuations exhibit a wide range of time scales and a power-law spectrum, resulting from the complex many-state kinetics of the underlying proteins. The effective number of channels that can respond to the voltage field is a dynamical variable which depends on the channels activity and the control parameters. This fact allows a biological system to use the proteins internal degrees of freedom in a selective way, applying constraints on the way their kinetics show up in the macroscopic dynamics of the system.