EFFECT OF DNP ON NEURO-MUSCULAR JUNCTION OF FROG.

Abstract

Endplate potential can be regarded as one of the indications of the transmitter output in the nerve terminal. By observing the pattern of successive e. p. p. evoked by tetanic stimulation of the frog nerve under various conditions, the report on the state of nerve terminal concerning the quantity of transmitter released was given by Wakabayashi and Iwasaki in this jounal. In the present report the characteristic effect of a metabolic inhibitor: 2-4 DNP on e. p. p. pattern is presented, and the mode of action of this drug different from other inhibitors or excess potasium is discussed. This drug reduces e. p. p. size but increases m. e. p. p. frequency as reported by Kraatz and Trautwein. Here the marked facilitation followed by steep depression showing a bell pattern was observed. The train of e. p. p. decreased in size by every repetition of tetaniza-tion. It indicates the exhaustion of available transmitter, and really long time was necessary to recover the original pattern. The bell pattern was characteristic of 2-4 DNP, and the action of other inhibitors, Ca++ deficiency or Mg++ addition did not bring about such an effect. From this, the mode of action of DNP cannot be explained only by the inhibition of oxydative trans-phosphyrolyation or reduced output of transmitter. On the other hand the Ach sensitivity was found unchanged in DNP muscle by measuring the depolariza-tion. In fact, m. e. p. p. in DNP muscle showed increase in frequency or burst at the certain decreased level of resting potential. Therefore, the site of action of DNP may not be postsynaptic and some specific inhibition of synthesis or supply of transmitter is suggested.