THE PROBLEM OF IMPULSE CONDUCTION IN THE ATRIUM 133 



EFFECTS OF ACETYLCHOLINE ON CURRENT SPREAD 



Two-dimensional mapping of current spread is a useful tool for studying 

 drug actions on the atrium. Figure 4 shows the effects of 10 "^ (w/v) acetyl- 

 choline on the 3 mV/'/iA isopotential line of a rat trabecula. It is seen that 

 the acetylcholine reduced the spread of current to about one-half in both the 

 parallel and the perpendicular direction. Such a finding raises the not \cry 



Trobeculo 



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Fio. 4. Isopotential contours on the surface of a trabecula, showing the effect ol' 

 acetylchohne on current spread. The heavy lines show the boundaries of the 

 trabecula. The map is constructed partly from the data shown in Fig. 2; round 

 points, parallel to fiber direction; square points, perpendicular to it. The numbers 

 by each point give the potential per unit current for that point ; those in paren- 

 theses refer to measurements made when acetylcholine was added to the bathing 

 medium (10 '^w/v). The outer contour is the 3 k J.2 control contour and the 

 inner the 3 kii acetylcholine contour. Note the increased spread in the direction 

 of the branch of the trabecula at the left. 



