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Anatomy Other topics and Adverse effects 99582ca6

Which of the following statements is not true of local anaesthetics?

A
The local anaesthetic is required in the unionized form for penetrating the neuronal membrane
B
The local anaesthetic approaches its receptor only from the intraneuronal face of the Na+ channel
C
The local anaesthetic binds to its receptor mainly when the Na+ channel is in the resting state
D
The local anaesthetic combines with its receptor in the ionized cationic form
High-Yield Explanation
(Ref: KDT 6/e p352, 353) All LAs are weak bases. LAs act by blocking Na' channels from inside the neuron (intra-neuronal face). These can cross the membrane only in unionized (lipid soluble) form. Sodium bicarbonate is therefore added to make the LA rapid acting. Once inside the neuron, LAs again gets ionized and bind to Na+ channels. Binding to Na+ channels is more in repetitively firing neurons than in resting neurons.
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