Ameiiican Journal of Piiysiology

HAYS, E. T., T. M. DWYER, P. EIOROWICZ, AND J. G. SWIFT, Epinephrine action on sodium fluxes in frog striated muscle. Am. J. Physiol. 227(6) : 134-O-1347. 1974.-Both sodium efflux and influx were measured on sartorius muscles freshly isolated from frogs. In normal Ringer fluid epinephrine in concentrations above 3 pg/ml maximally increased sodium efIlux by 45y0. At 15 pg/ml epinephrine decreased sodium influx by about 13 yO. The percentage increase in sodium efflux produced by epinephrine was quantitatively the same in sodium-free, lithium-containing solutions. The stimulation in efflux produced by epinephrine in normal Ringer fluid was completely inhibited by strophanthidin; in fact, epinephrine produced a 20% reduction in the strophanthidin-insensitive sodium efUux. On the other hand, epinephrine had no measurable effect on sodium efflux in sodiumfree solutions when strophanthidin was present. From these findings it is concluded that epinephrine stimulates the active transport system for sodium while inhibiting the strophanthidininsensitive sodium-for-sodium exchange which is present in frog muscle. The stimulation in active sodium transport produced by epinephrine can be ascribed neither to a release of the inhibition which external sodium normally has on the sodium pump nor to an increased internal sodium concentration.