ABSTRACT
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, PCI/PK, measured at acclimation temperature, was approximately 7·0 after acclimation at 25 °C and 1·3 after acclimation at 7°C. This difference was due to a six-fold reduction in the membrane chloride conductance upon acclimation to 7 °C as compared to 25 °C-acclimated fibres. Mean (±S.E.M.) values of the chloride conductance were 554 + 68μS cm−2 in warm-acclimated sunfish, and 75 ± 9μ.Scm−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 °C-acclimated sunfish to holding tanks at 7 °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°C-acclimated sunfish, transferred to 25 °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.
