On the local anaesthetic effect of barbiturates

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Abstract
Controversy exists about whether the free acid (non-ionized) or the anionic (ionized) form of barbiturates abolish the excitation of nerves. The experiments made showed that sodium pentobarbitone and sodium phenobarbitone are more effective at pH 6·8 than 8·8 in blocking the action potential in the desheathed frog nerve. The experimental procedure employed excludes the possibility that this difference in activity is due only to a more effective rate of penetration of the non-ionized form across the nerve membrane. In the same preparation these barbiturates at both pH 6·8 and 8·8 did not interfere with the uptake and release of radiocalcium. These data suggest that barbiturates block the action potential by increasing the surface pressure of the lipid layer of the excitable membrane and do not interfere with the calcium binding to sites which govern the increased membrane conductance during excitation.