Phase transitions in biological membranes

TL;DR

This paper reviews how phase transitions in biological membranes occur near physiological temperatures, affecting membrane properties and functions, and discusses thermodynamic control mechanisms influencing these transitions.

Contribution

It provides a comprehensive review of experimental findings and thermodynamic principles governing membrane phase transitions and their impact on membrane function.

Findings

Membranes exhibit melting transitions 10-20°C below body temperature.

Transitions influence membrane permeability and mechanical properties.

Environmental factors can modulate transition temperatures.

Abstract

Native membranes of biological cells display melting transitions of their lipids at a temperature of 10-20 degrees below body temperature. Such transitions can be observed in various bacterial cells, in nerves, in cancer cells, but also in lung surfactant. It seems as if the presence of transitions slightly below physiological temperature is a generic property of most cells. They are important because they influence many physical properties of the membranes. At the transition temperature, membranes display a larger permeability that is accompanied by ion-channel-like phenomena even in the complete absence of proteins. Membranes are softer, which implies that phenomena such as endocytosis and exocytosis are facilitated. Mechanical signal propagation phenomena related to nerve pulses are strongly enhanced. The position of transitions can be affected by changes in temperature, pressure, pH and salt concentration or by the presence of anesthetics. Thus, even at physiological temperature, these transitions are of relevance. There position and thereby the physical properties of the membrane can be controlled by changes in the intensive thermodynamic variables. Here, we review some of the experimental findings and the thermodynamics that describes the control of the membrane function.