Temperature adaptation of biological membranes: differential homoeoviscous responses in brush-border and basolateral membranes of carp intestinal mucosa.

The effects of temperature acclimation of carp upon the hydrocarbon order of intestinal membranes has been determined. A fractionation technique has been developed for the simultaneous purification of brush-border and basolateral membrane fractions from the intestinal mucosa. The specific activity of alkaline phosphatase in the brush-border fraction was enhanced 6.4-fold over that of the initial homogenate, whilst the (Na(+)-K+)-stimulated ATPase was enhanced 5.8-fold in the basolateral fraction. The specific activities of NADPH-cytochrome-c reductase, succinate-cytochrome-c reductase and acid phosphatase were not increased in these two fractions. Membrane hydrocarbon order in membranes from 10 and 30 degrees C-acclimated carp has been compared by measuring the steady-state fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene over a range of temperatures. In the brush-border fraction, polarization was identical in both cold- and warm-acclimated groups, whilst large differences were observed in the basolateral fraction sufficient to offset approx. 75% of the temperature-induced ordering effects of cold. The fatty acid composition of the major phosphoglyceride fractions in the brush-border fraction was also largely unaffected by thermal acclimation, whilst the basolateral fraction showed significant increases in the proportion of unsaturated fatty acids in the cold. It is concluded that whilst the basolateral membrane of intestinal mucosa displays a large homoeoviscous response that correlates with a shift in lipid composition, the brush-border membrane does not. These findings are consistent with evidence of functional adaptations of the basolateral membrane during thermal acclimation (Gibson, J.S., Ellory, J.C. and Cossins, A.R. (1985) J. Exp. Biol. 114, 355-364).