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

The effects of catecholamines on active sodium and potassium transport was compared in slow- (SOL) and fast-twitch (EDL) skeletal muscles of the rat. Stimulation of active Na+-extrusion and K+-uptake induced by adrenaline (6-30 mumol . l-1) and isoprenaline (1-40 mumol . l-1) was markedly greater in slow- than in fast-twitch muscle. In sodium-preloaded muscles the maximal stimulation of 24Na-efflux induced by adrenaline was about 2-fold higher in SOL than in EDL. Isoprenaline caused a 2.4-fold increase in ouabain-sensitive 86Rb influx in SOL muscle, but failed to alter the ouabain-sensitive influx in EDL. The stimulating action of isoprenaline on 86Rb 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.