Differences in lipid composition and fluidity of cardiac sarcolemma prepared from newborn and adult rabbits.

As the lipid composition of sarcolemma isolated from the rabbit heart changes during ontogeny, the object of this study is to determine if concomitant changes in sarcolemmal fluidity occur. Highly purified sarcolemmal fractions of newborn and adult myocardium were prepared and lipids of those fractions were analyzed. The fluorescence anisotropy of sarcolemmal fractions of both groups was also measured on a fluorometer using 1,6-diphenylhexatriene (DPH) as a probe. Total phospholipid, cholesterol, total fatty acid, and saturated fatty acid contents in the sarcolemmal fraction of the newborn were significantly higher than those of the adult. Total fluorescence intensity at saturating levels of DPH was significantly higher in the sarcolemmal fraction isolated from the newborn compared to the adult, but anisotropy was not significantly different between the newborn and the adult. An Arrhenius plot demonstrated phase transition points at nearly 23 degrees C in both myocardium, but an apparent phase transition at breaking point was not observed in the newborn sarcolemmal fraction. The slight difference in the value of the fusion activation energy above and below the phase transition point was observed between the newborn and the adult. Thus, it is apparent that the changes of sarcolemmal fluidity with age do occur but are smaller than expected, based on the difference in the sarcolemmal lipid composition.