Sunday, April 18, 2010

Once Again


Kaplan says: Local anesthetics bind preferentially to activated Na channels.

First aid says: Local anesthetics bind preferentially to INactivated Na channels.

So who's right? Once again, both are correct! According to Katzung Basic and Clinical Pharmacology (LANGE), local anesthetics have an increased affinity for BOTH activated and inactivated states of Na channels, but they have a low affinity for resting Na channels. Remember that Na channels in the heart and neurons have 3 states according to their M and h gates (resting, activated, and inactivated). Neurons with higher rates of firing have more Na channels in the activated and inactivated states, and less in the resting/ready state.

1 comment:

  1. Lidocaine in particular is highly frequency dependent, in that it has more activity with increasing heart rates. This is because lidocaine selectively blocks Na channels in their open and inactive states and has little binding capability in the resting state.