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r/step1•
fifaproblems

How do nondihydropyridines decrease phase 4 nodal depolarization when they are L-type selective and phase 4 is funny current and T-type Ca+ channels?

Posted May 26, 2020, 6:05 PM UTC

11
Jvalgreen69•

Phase 4:

  1. funny Na currents open due to hyperpolarization
  2. Bringing a slow depolarization until the RMP reaches about -50 and T-type channels open
  3. the influx of t type ca brings the RMP to threshold about -40 or a bit more positive
  4. Once there the L-type ca channels open leading to the action potential
  5. So if u block the Ltype ca channels it will slow phase 4 and phase 0.
  6. Depends also, that Verapamil for example blocks AV node prefrentially over the SA node, as to why it prolongs the ERP and AP in the AV node and not SA node.
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