The effects of urea and trimethylamine N-oxide on fluidity of liposomes and erythrocyte membranes of an elasmobranch (Raja erinacea). Am.J.Physiol

fluidity of liposomes and membranes of an elasmobranch. Am. J. Physiol. 276 (Regulatory Integrative Comp. Physiol. 45): R397–R406, 1999.—The effects on membrane fluidity of two solutes of biological importance in elasmobranch fishes, urea and trimethylamine oxide (TMAO), were determined using elasmobranch red blood cell plasma membranes and artificial liposomes. Fluorescence polarizations of three probes with differing sites of insertion (1,6-diphenylhexatriene, cis-parinaric acid, and trans-parinaric acid) were used to study the effects of physiological levels of urea (400 mM) and TMAO (200 mM) separately and together in a 2:1 urea:TMAO ratio (400 mM:200 mM). In the elasmobranch erythrocyte mem-brane, there was a trend toward an increase in the order of the gel-phase domains when treated with urea, although this was not statistically significant. This effect was counteracte