An Investigation of the Action of Diphenylhydantoin on Sodium Efflux in Barnacle Muscle Fibres

B ittar , E. E., S. S. C hen , B. G. D anielson AND E. Y. T ong . An investigation of the action of diphenylhydantoin on sodium efflux in barnacle muscle fibres. Acta physiol. scand. 1973. 89. 30–38. Sodium efflux from barnacle fibres is suppressed by external but not by internal application of diphenylhydantoin (DPH). DPH (10 ‐4 M) at pH 7.8 reduces the Na efflux by 32 %, a value slightly less than half that obtained with 10 ‐4 M ouabain. Ouabain has the ability to abolish the remaining Na efflux, whereas DPH incompletely abolishes the ouabain‐insensitive Na efflux. The onset of inhibition by DPH is slower than that by ouabain. At lower external pH the onset of peak action by DPH is more rapid than at pH 7.8. The sensitivity of the Na efflux to DPH is unaffected by external K. However, the residual efflux from fibers poisoned with ouabain following K removal is insensitive to DPH. DPH prevents the Na efflux from responding to external acidification. It also has the power to almost completely reverse the effect of external acidification on the Na efflux. It is provisionally concluded that the T‐system is the site of DPH action.