The effects of temperature acclimation on the resting membrane of skeletal muscle fibres from green sunfish.

Conductive properties of muscle fibres from green sunfish (Lepomis cyanellus) acclimated to different temperatures were examined. The relative membrane permeability to chloride and potassium ions, PCl/PK, measured at acclimation temperature, was approximately 7.0 after acclimation at 25 degrees C and 1.3 after acclimation at 7 degrees C. This difference was due to a six-fold reduction in the membrane chloride conductance upon acclimation to 7 degrees C as compared to 25 degrees C-acclimated fibres. Mean (+/- S.E.M.) values of the chloride conductance were 554 +/- 68 microseconds cm-2 in warm-acclimated sunfish, and 75 +/- 9 microseconds cm-2 in cold-acclimated sunfish. Membrane capacitance also differed significantly between the two acclimation groups. When the temperature was varied acutely, the magnitude of the chloride conductance exhibited a maximum Q10 of only 1.9, compared with a Q10 of 3.0 associated with acclimation. Upon transferring 25 degrees C-acclimated sunfish to holding tanks at 7 degrees C, the total membrane resistance exhibited a sigmoidal increase over about 14 days, and a steady membrane capacitance was achieved in about 10 days. For 7 degrees C-acclimated sunfish, transferred to 25 degrees C, resistance showed a sigmoidal decrease over 10 days and capacitance was steady after 8 days. The results indicate that thermal acclimation of the muscle membrane involves cellular regulatory processes which underlie significant changes in the electrical properties of the fibre.