Variable homeoviscous responses of different brain membranes of thermally-acclimated goldfish.

The effects of thermal acclimation of goldfish upon the bulk fluidity of synaptic, mitochondrial and myelin membrane fractions of brain was determined using steady-state and differential polarised phase fluorimetry. Membrane fluidity decreased in the order, mitochondria greater than synaptic membranes greater than myelin. in each case membranes from cold-acclimated goldfish were more fluid than the corresponding membranes of warm-acclimated goldfish, though the adjustment of fluidity in each case was insufficient to compensate for the direct effects of the temperature difference. The extent of fluidity compensation was greatest in the mitochondrial fraction and least in the myelin fraction, indicating heterogeneous responses in different membrane-types. Steady-state and dynamic fluorimetric techniques provided identical estimates of the homeoviscous responses, indicating that despite its short-comings, the steady-state technique provided as good a measure of adaptive responses as the more complex and sophisticated technique.