Cyanide Inhibition of Frog Tissues ∗

Abstract

Some time ago it was reported that cyanide produces practically complete inhibition of nerve respiration and that when lower grades of inhibition were observed this was attributable in large part to escape of cyanide into the alkali in the inset. 1 Recently it became desirable to construct a vessel which would permit a study of cyanide inhibition in which preliminary determinations of resting respiration could be carried out in the complete absence of cyanide from the vessel. This was accomplished by the use of a dosing stopcock to contain the cyanide which was placed in the bottom of the vessel so that at any moment by turning this stopcock cyanide would diffuse into the fluid bathing the tissue. When cyanide inhibition of frog nerve respiration was studied, not only was the previous report of complete inhibition confirmed, but even very low concentrations of cyanide had considerable effect. Such low concentrations could not be studied with the previous method because of escape of HCN. The inhibitions obtained with other tissues were also higher than those reported by others.

At the outset of the experiment the hollow dosing stopcock, greased and inserted into the female member with the opening facing downwards, is completely filled with neutralized buffered sodium cyanide by means of a capillary pipette. The stopcock is then turned through 90°. The nerves or other tissue to be studied are then placed in the main vessel in 1.0 cc. of phosphate Ringer, 5% KOH being placed in the side arm for absorption of CO₂. The vessels are placed on differential manometers and a curve of resting respiration determined. After obtaining a satisfactory line for resting respiration the dosing stopcocks of the control and experimental vessels are turned so that the opening is now to the vessels permitting diffusion of cyanide into the fluid around the tissue.