Let's move on. Question 9. Figure 9.1 shows activation maps on the left and action potentials on the right, recorded in a monolayer of ventricular cardiomyocytes at three different pacing cycles. Which of the following best explains the rate-dependent effects on conduction velocity and the action potential duration at 80 percent recovery, or APD80? Let's go to the figure. These are the activation maps shown on the left, and these are the action potentials. These are optical action potentials recorded at three different pacing cycle lengths, 1,500 milliseconds, 1,000 milliseconds, 500 milliseconds. The action potential durations are shown here, and the conduction velocities in each case are shown here. Let me give you a minute to go over this. Back to the question. Which of the following best explains the rate-dependent effects on the conduction velocity and APD80? A, synthetic activation of repolarizing currents. B, cumulative inactivation of delayed rectifier potassium currents, particularly IKS. C, depletion of calcium from the sarcoplasmic reticulum, which reduced calcium-dependent inactivation of L-type calcium currents. Or D, cumulative inactivation of the sodium current. Let's go back again to the traces, or to the figure. Again, to the potential responses.

ventricular cardiomyocytes

pacing cycle lengths

conduction velocity

action potentials

rate-dependent effects