Membrane tubes with active pumping: water transport, vacuole formation and osmoregulation

TL;DR

This paper models active membrane tubes with ion pumps and channels to understand water transport and vacuole formation, providing insights into osmoregulation in freshwater organisms.

Contribution

It introduces a simple membrane tube model with active pumping to explain vacuole formation and water regulation mechanisms in protists.

Findings

Membrane tubes with ion pumps can form large vacuoles.

Active pumping enables water removal from cells.

Model offers a minimal system for osmoregulation.

Abstract

The need for organisms to regulate their volume and osmolarity when surrounded by freshwater is a basic physical challenge for many bacteria, protists and algae. Taking inspiration from the contractile vacuole complex found in many protists, we discuss how simple models of active membrane tubes can give insights into the fluid and active ionic transport properties of such systems. We show that a simple membrane tube with unidirectional ion pumps, and passive ion and water channels, forms a large vacuole due to osmotically-driven water flow and that this can be used to actively pump water out of the cell interior. We discuss the use of this system as a possible minimal method for osmoregulation.