ABSTRACT
The L-glutamate concentration in blood plasma of the crayfish, Astacus lepto-dactylus and A. astacus, was found to be about 1·5 ×10−6M, as measured by a specific enzymatic method. Even 10 times this concentration of L-glutamate in saline failed to significantly affect neuromuscular transmission in the dactyl abductor muscle, although higher concentrations caused depression.
L-Glutamate in the blood plasma of the spider, Dugesiella hentzii, amounted to 7 × 10−6M. As in the crayfish, even 10 times this concentration of L-glutamate in saline failed to affect neuromuscular transmission in the promotor tibiae muscle, while higher concentrations caused depression.
The concentration of L-glutamate in Locusta migratoria blood plasma, ca. 7 ×10−6M, would appear to be sufficient to cause depression of neuromuscular transmission in vivo. Perfusion of the extensor tibiae preparation with 15 ×10−6ML-gluta-mate caused marked depolarization and decreases in the size of e.j.p.s.
It appears that in the tarantula and the crayfish, blood plasma L-glutamate does not pose difficulties for neuromuscular transmission. In the locust, additional protective mechanisms which are not able to function in the saline-perfused in vitro preparation must be at work in the living animal.
