The influence of catecholamines on Na, K transport in slow- and fast-twitch muscles of the rat

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Abstract
The effects of catecholamines on active sodium and potassium transport was compared in slow- (SOL) and fasttwitch (EDL) skeletal muscles of the rat. Stimulation of active Na+-extrusion and K+-uptake induced by adrenaline (6–30 μmol · 1−1) and isoprenaline (1–40 μmol · l−1) was markedly greater in slow- than in fast-twitch muscle. In sodiumpreloaded muscles the maximal stimulation of24Na-efflux induced by adrenaline was about 2-fold higher in SOL than in EDL. Isoprenaline caused a 2.4-fold increase in ouabainsensitive86Rb influx in SOL muscle, but failed to alter the ouabain-sensitive influx in EDL. The stimulating action of isoprenaline on86Rb influx in EDL was due to an increase in the ouabain-insensitive fraction of Rb uptake. The effects of catecholamines of fast- and slow-twitch muscles were probably due to the accumulation of cyclic AMP, however the fact that there were no significant differences between the nucleotides levels in fast- and slow-twitch muscle suggests the participation of other mechanism as well. The results presented suggest that cyclic AMP-induced stimulation of ouabain-insensitive transport of cation in the isolated EDL muscle of the rat is similar to that of barnacle muscle.