L-glutamine: an amino acid required for maintenance of the tegumental membrane potential of Schistosoma mansoni.

The tegumental membrane potential (-63 +/- 2.9 mV) of adult male Schistosoma mansoni in RPMI-1640 is significantly depolarized (-26 +/- 7.3 mV) when the parasite is incubated in inorganic media (Hank's Balanced Saline or RPMI-1640 without organic constituents). Of 9 amino acids (L-glutamine, D-glutamine, L-arginine, L-proline, L-aspartate, L-glutamate, L-asparagine, L-isoleucine and L-methionine) L-glutamine alone is sufficient to repolarize the membrane potential to a value (-56 +/- 4.5 mV) not significantly different from that found in RPMI-1640. Repolarization by glutamine is dose-dependent, with significant effects obtained as low as 0.10 mM. The concentration of phosphate in the medium also significantly alters the membrane potential. Physiological levels of phosphate (5.6 mM) are necessary in conjunction with L-glutamine to obtain the full repolarization of the membrane potential. In the absence of organic constituents, the membrane potential is strongly dependent on the external medium pH. When L-glutamine is present in the medium, the membrane potential becomes virtually independent of the external pH.