Active transport of sodium and potassium in Na-loaded skeletal muscles of potassium-deficient rats.

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1. The active transport in Na-rich SOL and EDL muscles of K-deficient rats was studied by soaking the muscles in 10mM-K fluid with or without various agents at 30°C or at various temperatures for 2 hr.2. The active transport in Na-rich muscles of K-deficient rats after recovery was greater than that of normal rats, made Na-rich by soaking the muscles in cold K-free fluid for 2hr. Na extrusion and K uptake in Na-rich SOL muscles of K-deficient rats during recovery were greater than those in EDL muscles.3. Na extrusion in Na-rich EDL muscles during recovery was fully inhibited at temperature ranging from 1 to 11°C, while K uptake was inhibited partially at 11°C.4. The rate constant of Na extrusion during a recovery period of 0-30min were 2.19hr-1 in SOL muscles and 2.15hr-1 in EDL ones.5. The Na-K exchange in Na-rich muscles of K-deficient rats does not appea to occur on a simple one-to-one basis.6. Addition of ouabain (0.001mM), IAA (0.2mM) and FDNB (0.03mM) to the recovery fluid produced marked inhibition on the active transport in Na-rich SOL muscles. Presence of aspartate ion facilitated the active transport, but pyruvate and glutamate ions had no effect.7. Acetylcholine (8μg/ml) increased the active transport in Na-rich EDL muscles during recovery, whereas succinylcholine (2μg/ml) inhibited it. Little effect by tubocurarine (3μg/ml) was observed.8. FDNB (0.005mM)-treated Na-rich SOL muscles showed the action potential of a smaller amplitude and of a longer duration. Tetrodotoxin (0.08μg/ml) abolished the action potential of Na-rich EDL muscles and produced delayed rectification by a strong cathodal current.