Studies on neuromuscular transmission and the effects of lack of potassium

Abstract

An investigation has been made of the effect of low extracellular potassium concentration on the functioning of the rat diaphragm phrenic nerve preparation, at 24°C.

Potassium free bathing solution causes an augmentation of the mechanical response of the muscle under conditions of indirect tetanic stimulation. A cyclic stimulation procedure is described consisting of alternate 1 Hz and 50 Hz stimulation. Using this procedure the augmentation of the tetanic response is particularly evident both in amplitude and maintenance of tension.

Investigations have also been made using intracellular recording techniques. Potassium free solution has been shown to cause an increase in the amplitude of the curare blocked end-plate potential greater than the increase which its action on the resting potential would predict. Removal of potassium has little action on the miniature end-plate potential amplitude recorded from the junction under resting conditions.

Experiments using paired stimuli have demonstrated a differential, amplitude enhancement of the second end-plate potential at intervals between 5 m.sec and 600 msec. The effect of potassium free solution was shown to be different from that of increased calcium concentration, and to reverse the depression of amplitude caused by this under these conditions.

By the use of short trains of stimuli under conditions of low potassium, an increase in the immediately available store of transmitter has been inferred. This increase was augmented in some cases by the addition of choline to the bathing solution.

The action of both d-Tubocurarine and Hemicholinium-3 on the mechanical response of the preparation has been shown to be similar, using the cyclic stimulation procedure, and opposite to that of potassium free solution.

An hypothesis is suggested linking the augmentations observed to an effect on the presynaptic store of transmitter in the nerve terminal caused by an increase of transmitter synthesis under potassium free conditions.