SCHISTOSOMA-MANSONI - L-GLUTAMATE-INDUCED CONTRACTIONS IN ISOLATED MUSCLE-FIBERS - EVIDENCE FOR A GLUTAMATE TRANSPORTER

Schistosoma mansoni muscle fibers contract in response to L-glutamate in a dose-dependent manner (10(-6)-10(-3) M). L-aspartate and D-aspart ate are likewise effective in eliciting contraction of the fibers, Mam malian glutamate receptor agonists produce little or no contraction at concentrations as high as 1 mM. In addition, common glutamate recepto r antagonists do not inhibit the contraction induced by L-glutamate. H owever, amino acids known to be substrates for the high-affinity gluta mate transporter elicit contraction of the muscle fibers. These result s suggests that there is a high-affinity glutamate transporter on the muscle fibers which, because of its electrogenic nature, is causing de polarization and contraction. This is supported by the evidence that c ontraction induced by L-glutamate is dependent on extracellular Ca2+ a nd is blocked by nicardipine (10 mu M) [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 transporte r. This experimental evidence supports the hypothesis that there is a Na+-dependent high-affinity glutamate transporter on the schistosome m uscle membrane. (C) 1996 Academic Press, Inc.