Automaticity

• (1) increasing the maximum diastolic membrane potential

• (2) decreasing the slope of phase 4 depolarization

• (3) increasing action potential duration

• (4) raising the threshold potential

  • All of these factors make it take longer or make it more difficult for the membrane potential to reach threshold.

    • (1) The diastolic membrane potential may be increased by adenosine and acetylcholine.

    • (2) The slope of phase 4 depolarization may be decreased by beta receptor blockers

    • (3) The duration of the action potential may be prolonged by drugs that block cardiac K⁺ channels

    • (4) The membrane threshold potential may be altered by drugs that block Na⁺ or Ca²⁺ channels.

Category: Pharmacology Notes