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 é® 
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.