Kinetics of nerve impulse blocking by protein cross-linking aldehydes. Apparent critical thermal points

The effect of formaldehyde, crotonaldehyde, butyraldehyde, glutaraldehyde and cinnamaldehyde on the compound action potential of frog sciatic nerve was studied in the temperature domain 20-35 degrees C at various aldehyde concentrations. All these reagents gradually decrease the amplitude of nerve action potential, up to the complete block, the order of effectiveness being: crotonaldehyde greater than cinnamaldehyde greater than butyraldehyde greater than formaldehyde greater than glutaraldehyde. The effect of cinnamaldehyde is almost completely reversible, while all others have irreversible action. The dependence of the blocking time on temperature and concentration is well expressed in all cases by the same empirical equation. This dependence points to the existence of critical temperatures, specific for each aldehyde, at which impulse blocking would be instantaneous, regardless of concentration. These temperatures (obtained by extrapolation) lie between 43 degrees C (for crotonaldehyde) and 57.5 degrees C (for butyraldehyde). The existence of free amino groups within ionic channels, as main sites of aldehyde attack, is inferred.