On the mechanism of a long-lasting neuromuscular depression in crayfish

Abstract

1. Long-lasting depression of neuromuscular transmission was studied in giant motoneuron-fast abdominal flexor muscle preparations of the crayfish Procambarus clarkii. 2. The depression is not modified in the presence of high concentration of picrotoxin, which blocks the effect of the only known putative inhibitory transmitter GABA. This result eliminates the possibility that the depression is due to an inhibitory process. 3. The decrease of preparation temperature reduces or abolishes the depression. The effect is not due to reduction of the transmitter output due to the cooling. These results suggest that the depression is dependent upon the cell's metabolism. 4. The depression is also reduced in the presence of high concentration of 2,4-dinitrophenol or ouabain. These drugs are known to result into increasing the intracellular [Ca 2+]. 5. It is concluded that the long-lasting depression might be in part related to the concentration of [Ca 2+] in the axon terminals.