© 1998 by The Society for Integrative and Comparative Biology
Cholesterol Function in Plasma Membranes from Ectotherms: Membrane-Specific Roles in Adaptation to Temperature1
Department of Biological Sciences, Ohio University Athens, Ohio 45701
Correspondence: 2 E-mail: crockett{at}oak.cats.ohiou.edu
SYNOPSIS. Cholesterol is an essential component in the plasma membranes of animals with multiple effects on the physical properties of membranes including membrane order (fluidity), phase behavior, thickness, and permeability. Cholesterol also affects functional attributes of cell membranes such as the activities of various integral proteins. Because cholesterol provides rigidity to fluid phase membranes, it is a likely candidate to counter some of the temperature-induced perturbations in membrane order that would otherwise be experienced by animals that live at varied body temperatures. If cholesterol contributes to homeoviscous adaptation (HVA), more cholesterol is likely to be present in plasma membranes from warm-bodied animals than from cold-bodied animals. This prediction is generally supported by studies examining cholesterol contents in membranes from endothermic and ectothermic animals. Comparisons of cholesterol levels in temperature acclimated (oracclimatized) ectotherms reveal an increase in cholesterol with temperature, no change in cholesterol content, or an increase in cholesterol with a decrease in temperature. These different patterns largely represent tissue and regional differences in the membranes (membrane domains). The membranespecific nature of the cholesterol response to temperature is likely to arise from the multiplicity of the effects that cholesterol exerts on membranes, as well as the heterogenous nature of plasma membranes. These factors also allow cholesterol to perform more than a single role in temperature adaptation of plasma membranes in animals.