REPOLARISATION ASSAYS

SINGLE VENTRICULAR MYOCYTES

EFFECTS OF VERAPAMIL ON ACTION POTENTIAL DURATION

Figure 1 The effects of verapamil on action potential duration.

Figure1   shows action potential records taken from a single left ventricular myocyte under our standard experimental conditions used for the action potential measurements in the absence (black) and presence (red) of verapamil (1 鮠
Verapamil (1, 10 and 100  鬠caused a concentration-dependent shortening of APD90 and APD50 at 1 Hz.  The effects of verapamil on APD90 and APD50 are summarised in Figure 2.
Verapamil appeared to elicit greater shortening of APD50 than of APD90.  Verapamil caused a significant (p<0.05) reduction in maximal rate of depolarisation (MRD) at all concentrations used (100  ࣡used a 69.4 ⮳% reduction).

   
 

Figure 2   Mean data for the effect of verapamil on APD50 and APD90.

 
 

Figure 2    Verapamil, like nifedipine, caused a concentration-dependent decrease in APD50 and APD90.  Unlike nifedipine, however, verapamil also decreased MRD by 69.4 ⮳%.  In the case of verapamil, block of both the inward calcium current and of sodium current may contribute to shortening of the action potential.

 

 
     
     
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