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-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 microM). [3H]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 [3H]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.
Miller
C L
CL
Department of Pharmacology & Toxicology, Michigan State University, East Lansing 48824, USA.
Day
T A
TA
Bennett
J L
JL
Pax
R A
RA
D018528:ATP-Binding Cassette Transporters / Q000378:metabolism*; D027322:Amino Acid Transport System X-AG; D000818:Animals; D001692:Biological Transport; D004305:Dose-Response Relationship, Drug; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000502:physiology*; D017470:Receptors, Glutamate / Q000187:drug effects; D012550:Schistosoma mansoni / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D012964:Sodium / Q000494:pharmacology
D018528:ATP-Binding Cassette Transporters; D027322:Amino Acid Transport System X-AG; D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; D017470:Receptors, Glutamate; D018698:Glutamic Acid; D012964:Sodium