<prompt> Which of the following statements is not true of local anaesthetics?The local anaesthetic is required in the unionized form for penetrating the neuronal membraneThe local anaesthetic approaches its receptor only from the intraneuronal face of the Na channelThe local anaesthetic binds to its receptor mainly when the Na channel is in the resting stateThe local anaesthetic combines with its receptor in the ionized cationic form  <response>: Ref: KDT 6e 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. 