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C.L. Miller, T.A. Day, J.L. Bennett and R.A. Pax
Experimental Parasitology 84:410-419
Schistosoma mansoni muscle fibers contract in response
to L-glutamate in a dose-dependent manner (10(-6)-10(-3) M). L-aspartate
and D-aspartate are likewise effective in eliciting contraction
of the fibers, Mammalian glutamate receptor agonists produce little
or no contraction at concentrations as high as 1 mM. In addition,
common glutamate receptor antagonists do not inhibit the contraction
induced by L-glutamate. However, amino acids known to be substrates
for the high-affinity glutamate transporter elicit contraction
of the muscle fibers. These results suggests that there is a high-affinity
glutamate transporter on the muscle fibers which, because of its
electrogenic nature, is causing depolarization and contraction.
This is supported by the evidence that contraction induced by
L-glutamate is dependent on extracellular Ca2+ and is blocked
by nicardipine (10 uM) [H-3]L-glutamate is taken up in a dose-dependent
manner by the muscle fiber preparation. This uptake is also time-
and temperature-dependent. Both the L-glutamate-induced contractile
response and [H-3]L-glutamate uptake are Na+-dependent and can
be blocked by specific inhibitors of the high-affinity transporter.
This experimental evidence supports the hypothesis that there
is a Na+-dependent high-affinity glutamate transporter on the
schistosome muscle membrane.