Chloride efflux measurements in mammalian skeletal muscle

Abstract

A rapid sampling technique has been used to resolve the components of ³⁶Cl efflux from isolated extensor digitorum longus (EDL) muscles of young rats. Four distinct fluxes with apparent rate constants of 4.40 ± 0.02 min⁻¹ (k₁), 1.30 ± 0.04 min⁻¹ (k₂), 0.24 ± 0.04 min⁻¹, (k₃), and 0.048 ± 0.05 min⁻¹ (k₄) at 30°C were identified. Together, these fluxes accounted for the movement of more than 98% of exchangeable muscle chloride (Cl) ions. The muscle compartment associated with the fastest flux (k₁) contained 23% ± 2% of the total muscle Cl corresponding to the extracellular space as determined with inulin or mannitol. The compartment associated with k₂ accounted for 71% of the intracellular volume, and k₂ was assumed to represent ³⁶Cl efflux across the surface membrane. The rate constant k₂ was temperature‐dependent with a Q₁₀ of 1.11 between 5°C and 30°C. Acromatic carboxylic acids known to block sarcolemmal Cl conductance (G_cl) specifically lowered k₂ by 25% at 30°C, as did replacement of external Cl with nitrate.