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Time-Dependent Molecular Memory in Single Voltage-Gated Sodium Channel

Nayak, Tapan K and Sikdar, SK (2007) Time-Dependent Molecular Memory in Single Voltage-Gated Sodium Channel. In: Journal of Membrane Biology, 219 (1-3). pp. 19-36.

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Abstract

Excitability in neurons is associated with firing of action potentials and requires the opening of voltage-gated sodium channels with membrane depolarization. Sustained membrane depolarization, as seen in pathophysiological conditions like epilepsy, can have profound implications on the biophysical properties of voltage-gated ion channels. Therefore, we sought to characterize the effect of sustained membrane depolarization on single voltage-gated $Na^+$ channels. Single-channel activity was recorded in the cell-attached patch-clamp mode from the $rNa_v1.2a$ channels expressed in CHO cells. Classical statistical analysis revealed complex nonlinear changes in channel dwell times and unitary conductance of single $Na^+$ channels as a function of conditioning membrane depolarization. Signal processing tools like weighted wavelet Z (WWZ) and discrete Fourier transform analyses attributed a “pseudo-oscillatory” nature to the observed nonlinear variation in the kinetic parameters. Modeling studies using the hidden Markov model (HMM) illustrated significant changes in kinetic states and underlying state transition rate constants upon conditioning depolarization. Our results suggest that sustained membrane depolarization induces novel nonlinear properties in voltage-gated $Na^+$ channels. Prolonged membrane depolarization also induced a “molecular memory” phenomenon, characterized by clusters of dwell time events and strong autocorrelation in the dwell time series similar to that reported recently for single enzyme molecules. The persistence of such molecular memory was found to be dependent on the duration of depolarization. Voltage-gated Na+ channel with the observed time-dependent nonlinear properties and the molecular memory phenomenon may determine the functional state of the channel and, in turn, the excitability of a neuron.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to Springer.
Keywords: Voltage-gated sodium channel;Cell-attached patch-clamp;Conditioning depolarization;Pseudoperiodic oscillation;Autocorrelation;Molecular memory.
Department/Centre: Division of Biological Sciences > Molecular Biophysics Unit
Date Deposited: 04 Jun 2008
Last Modified: 27 Aug 2008 13:25
URI: http://eprints.iisc.ernet.in/id/eprint/14161

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