EFFECTS ON THE HEART 219 



fall (Fig. 1-22) (Gardner et al, 1954). A more complete analysis of the mem- 

 brane potential changes in rat atria was reported by Webb and Hollander 

 (1959) and the results are summarized in Table 1-35. The most sensitive 



Table 1-35 



Effects of Iodo acetate and Iodoacetamide on Transmembrane Potentials 

 AND Other Parameters of Rat Atrium 



" The change in the overshoot (the reversal of polarization at the peak of the action 

 potential) is given in millivolts. The original paper should be consulted for the methods 

 of measurement (Webb and Hollander, 1959). 



event is the repolarization of the action potential, and this has also been 

 noted by Liillmann (1959 a, b). The acceleration of the repolarization short- 

 ens the duration of the action potential, reduces the area, and diminishes 

 the degree of potential change imposed on the myocardial cells, which pre- 

 sumably by itself leads to a depression of the contractility, which may fall 

 to quite low levels without significant changes in the resting or action po- 

 tential magnitudes. The reduction in the overshoot is i)OSsibly due to the 

 onset of the faster repolarization. In addition to the shortening of the ac- 

 tion potential, there appears to be another factor reducing the contractility, 

 inasmuch as the depression is somewhat greater than predicted on the basis 



