116 



O. F. HUTTER 



Once dissected, the preparations were tied to a fine wire and placed in 

 Ringer's solution containing the isotope. They were then either left to "load" 

 for a given length of time and used for an experiment in which the outflow 

 of isotope was studied, or taken out at intervals, washed and counted in 

 order to follow the uptake of the isotope. As the electrical events during 

 vagus inhibition indicated an increase in potassium permeability our first 

 concern was to study the movement of ^-K. Fortunately, the normally low 

 concentration of potassium in the extracellular fluid and the thinness of the 

 preparation allow the exchange of ^'-K to be followed with ease. Thus control 

 experiments showed that the loss of isotope from the extracellular space is 

 virtually complete within 3 min exposure to inactive wash solution and 

 thereafter the efflux of ^'K usually proceeded in a practically exponential 

 manner for 1-2 hr. To test the action of acetylcholine in outflow experiments 

 it was added to one or two of the samples of inactive wash solution. Alter- 

 natively the sinus venosus was dissected with the vagi attached and arranged 

 in a wax bath allowing easy exchange of wash solution. 



Figure 1 shows the effect of vagus stimulation on the efflux of ^-K from a 

 frog's sinus venosus. During the first part of the experiment the preparation 



SOOOr 



^ 2000 



lOOO 



O 05 



O 



30 



60 

 Time Cmin ) 



90 



Fig. 1. Efflux of '^^K from a frog's sinus venosus into Ringer's solution. Abscissa, 

 time from removal of preparation from solution containing 2-7 mM labelled K. 

 Left ordinate, radioactivity of tissue on a logarithmic scale, obtained by adding 

 together the activity of the wash solutions and the final tissue count. Right 

 ordinate, fraction of labelled K in tissue lost per min. During the third wash 

 period the left vagus was stimulated at 10/sec. 



