Transport between im/mobile fractions shapes the speed and profile of cargo distribution in neurons

Adriano A Bellotti; Jonathan G Murphy; Timothy S O'Leary; Dax A Hoffman

doi:10.1016/j.bpr.2022.100082

Transport between im/mobile fractions shapes the speed and profile of cargo distribution in neurons

Biophys Rep (N Y). 2022 Oct 20;2(4):100082. doi: 10.1016/j.bpr.2022.100082. eCollection 2022 Dec 14.

Authors

Adriano A Bellotti^{1

2}, Jonathan G Murphy², Timothy S O'Leary¹, Dax A Hoffman²

Affiliations

¹ Department of Engineering, University of Cambridge, Cambridge, UK.
² Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland.

Abstract

Neuronal function requires continuous distribution of ion channels and other proteins throughout large cell morphologies. Protein distribution is complicated by immobilization of freely diffusing subunits such as on lipid rafts or in postsynaptic densities. Here, we infer rates of immobilization for the voltage-gated potassium channel Kv4.2. Fluorescence recovery after photobleaching quantifies protein diffusion kinetics, typically reported as a recovery rate and mobile fraction. We show that, implicit in the fluorescence recovery, are rates of particle transfer between mobile and immobile fractions (im/mobilization). We performed photobleaching of fluorescein-tagged ion channel Kv4.2-sGFP2 in over 450 dendrites of rat hippocampal cells. Using mass-action models, we infer rates of Kv4.2-sGFP2 im/mobilization. Using a realistic neuron morphology, we show how these rates shape the speed and profile of subunit distribution. The experimental protocol and model inference introduced here is widely applicable to other cargo and experimental systems.