Sedatives and Hypnotics · Pharmacology

How do barbiturates differ from benzodiazepines regarding their effect on the GABA-A receptor chloride channel?

  1. Barbiturates shorten the duration of channel opening and reduce total chloride flux
  2. Barbiturates increase the frequency of channel opening but not its duration, exactly like benzodiazepines
  3. Barbiturates increase the duration of channel opening and can act as GABA mimetics at high doses
  4. Barbiturates bind at the same site as benzodiazepines and act only when GABA is present
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Correct answer: Barbiturates increase the duration of channel opening and can act as GABA mimetics at high doses

Barbiturates increase the duration of chloride channel opening. At higher concentrations, they can directly activate the receptor even in the absence of GABA, which contributes to their lower therapeutic index and greater risk of respiratory depression.

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