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Direct measurement of torsional stiffness and conformational friction in ion channels

Measure directly the torsional stiffness of ion channels and the friction opposing their conformational changes during ion translocation in membranes to enable quantitative assessment of local heating and temperature differences predicted by ratchet-engine models.

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Background

Extending the ratchet-engine framework beyond ATP synthase requires quantitative parameters such as torsional stiffness and friction associated with conformational changes of ion channels. These parameters strongly influence predicted temperature differences via the model’s dependence on mechanical dissipation.

The authors explicitly state that such direct measurements for ion channels are currently lacking and reference a theoretical hydrodynamic model predicting substantial local heating per single-ion translocation, underscoring the need for empirical determination of these mechanical properties.

References

Although we currently lack direct measurements of the torsional stiffness of ion channels and the friction opposing their conformational changes, the theoretical hydrodynamic model developed by Chen et al. [86], which is distinct from ours, predicts that the translocation of a single sodium ion through the gramicidin A channel (25 Å in length and 2 Å in radius) under a 100 mV transmembrane potential could result in a local temperature increase of 25 ℃ per ion.

— Decoding the Hot-Mitochondrion Paradox (2507.16824 - Fahimi et al., 4 Jul 2025) in Section 3: Can IMM proteins other than ATP synthase be modeled as a ratchet engine? (late in section)