Both benzodiazepines and barbiturates enhance GABAergic transmission at the GABA-A receptor. The electrophysiological difference between them is:

• A Barbiturates increase the frequency of chloride channel opening, benzodiazepines increase its duration
• B Both act exclusively by increasing the frequency of channel opening
• C Benzodiazepines increase the duration of chloride channel opening, barbiturates increase its frequency ✓
• D Barbiturates block the chloride channel directly at high concentrations

Explanation

Benzodiazepines bind at the interface of alpha and gamma subunits and increase the frequency of GABA-gated chloride channel opening. Barbiturates bind at beta subunits and prolong the duration of each opening, and at high concentrations they open the channel independently of GABA, explaining their lower safety margin. Swapping these two effects is the classic trap in this question.

Reference: Katzung Basic and Clinical Pharmacology, 15th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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