Properties of the chloride conductance associated with temperature acclimation in muscle fibres of green sunfish.

Characteristics of the anion conductance of muscle fibres from green sunfish have been determined. The membrane conductance of fibres from sunfish acclimated to 25 and 7 degrees C was linearly related to the extracellular chloride concentration. The chloride conductance exhibited a pH dependence which was adequately described by the titration of an acidic site with a pKa of 5.3 in 25 degrees C-acclimated fibres and 6.4 in 7 degrees C-acclimated fibres. The anion current-voltage (I-V) relationship of warm-acclimated fibres exhibited constant-field rectification, while the I-V relationship of cold-acclimated fibres was linear. In Ringer solutions containing elevated calcium concentrations (33 and 115 mmol 1(-1)), the I-V relationship of warm-acclimated fibres was similar to the control situation. However, the I-V relationship of cold-acclimated fibres showed a calcium concentration-dependent curvature in the direction expected for constant-field rectification. The voltage-dependence of the time constant of chloride current inactivation was shifted along the voltage axis by about 40 mV in the negative direction in 7 degrees C-acclimated fibres as compared to 25 degrees C-acclimated fibres. The results can be adequately described by a model of constant-field rectification with the inclusion of a term for the membrane surface potential. A simple hypothesis which can qualitatively account for many of these observations is that temperature acclimation alters the density of fixed negative surface charges in the vicinity of chloride channels.