Diffusive Exit Rates Through Pores in Membrane-Enclosed Structures

TL;DR

This paper introduces a simple model validated by simulations to estimate particle release rates through membrane pores, revealing how pore size, density, and length influence release efficiency, with applications to cellular calcium release.

Contribution

A novel approximate model for particle release rates through membrane pores, validated with stochastic simulations, applicable to various domain shapes and relevant to biological processes.

Findings

Low channel density suffices for significant release rates.

Increasing channel length reduces release rates and alters density dependence.

Model aligns with experimental calcium release measurements.

Abstract

The function of many membrane-enclosed intracellular structures relies on release of diffusing particles that exit through narrow pores or channels in the membrane. The rate of release varies with pore size, density, and length of the channel. We propose a simple approximate model, validated with stochastic simulations, for estimating the effective release rate from cylinders, and other simple-shaped domains, as a function of channel parameters. The results demonstrate that, for very small pores, a low density of channels scattered over the boundary is sufficient to achieve substantial rates of particle release. Furthermore, we show that increasing the length of passive channels will both reduce release rates and lead to a less steep dependence on channel density. Our results are compared to previously-measured local calcium release rates from tubules of the endoplasmic reticulum, providing an estimate of the relevant channel density responsible for the observed calcium efflux.