Voltage-Driven Alterations to Neuron Viscoelasticity

Abstract

Background: The consideration of neurons as coupled mechanical-electrophysiological systems is supported by a growing body of experimental evidence, including observations that cell membranes mechanically deform during the propagation of an action potential. However, the short-term (seconds to minutes) influence of membrane voltage on the mechanical properties of a neuron at the single-cell level remains unknown.

Materials and methods: Here, we use microscale dynamic mechanical analysis to demonstrate that changes in membrane potential induce changes in the mechanical properties of individual neurons. We simultaneously measured the membrane potential and mechanical properties of individual neurons through a multiphysics single-cell setup. Membrane voltage of a single neuron was measured through whole-cell patch clamp. The mechanical properties of the same neuron were measured through a nanoindenter, which applied a dynamic indentation to the neuron at different frequencies.

Results: Neuronal storage and loss moduli were lower for positive voltages than negative voltages.

Conclusion: The observed effects of membrane voltage on neuron mechanics could be due to piezoelectric or flexoelectric effects and altered ion distributions under the applied voltage. Such effects could change cell mechanics by changing the intermolecular interactions between ions and the various biomolecules within the membrane and cytoskeleton.

Keywords: mechanical-electrophysiological coupling; nanoindentation; neuron; patch clamp.

FIG. 1.

Schematic representation (A) and microscope image (B) of the simultaneous measurement of a single neuron's mechanical properties (through a nanoindenter) and electrophysiology (through whole-cell patch clamp); scale bar: 20 μm. (C) Storage and loss moduli (E′ and E″, respectively) and tanδ measurements of unclamped and clamped cells (no voltage was imposed by the clamp). E′ ± SE (Pa) is shown in black, E″ ± SE (Pa) in green, and tanδ ± SE in blue. Statistical analyses were performed between unclamped and clamped measurements at each frequency. Both E′ and E″ were significantly different between unclamped and clamped cells at each frequency, ***p < 0.001. SE, standard error.

FIG. 2.

(A) Example multiphysics experiment procedure over a 3.33 min time interval. A voltage is imposed through patch clamp (black, −100, −50, and 0 mV), while DMA (blue) at different frequencies is performed through nanoindentation on the same cell (duration 2.5 min for 6 frequencies). Before time 0, control DMA measurements are performed on the patched cell without any imposed voltage. (B) Frequency-dependent variation of storage modulus, E′ ± SE (Pa) in black, loss modulus, E″ ± SE (Pa) in green, and the loss tangent, tanδ ± SE in blue of neuronal cells for multiple membrane potentials (mV). (C) E′ (Pa), E″ (Pa), and tanδ ± SE as a function of membrane potential (mV) for each DMA frequency, n = [4–19]. Statistical analysis was performed between each voltage at a given frequency, *p < 0.05. Measured tanδ were not significantly different. DMA, dynamic mechanical analysis.