Transport of neurotransmitter precursors in a syncytial epithelium.
1. Tegumental transport of choline at concentrations ranging from 0.005-5.0 mM provided no evidence for saturable, carrier-mediated entry of this amine in the tegument of the rat tapeworm (Hymenolepis diminuta). 2. In contrast, the large neutral amino acid tryptophan appears to be taken up via a high-affinity transporter. In the 1st quartile of 17-day-old tapeworms (Km = 0.033 mM, Vmax = 0.7 nmol.min-1.g-1), in the 2nd quartile (Km = 0.015 mM, Vmax = 0.3 nmol.min-1.g-1), in the 3rd quartile (Km = 0.022 mM, Vmax = 0.5 nmol.min-1.g-1) and in the 4th quartile (Km = 0.025 mM, Vmax = 0.5 nmol.min-1.g-1) saturable tryptophan transport was kinetically characterized. 3. The non-saturable diffusion component (Kd) for tryptophan transport ranged from 3.8-10.2 microliters.min-1.g-1. 4. These studies suggest choline does not appear to be transported across the tapeworm tegument. Saturable transport of tryptophan via a high-affinity carrier is reported, and no regional variations in indole amino acid uptake were detected.
Cornford
E M
EM
S.W. Regional V.A. Epilepsy Center, Veterans Administration West Los Angeles Medical Center, CA 90073.
D000818:Animals; D001692:Biological Transport; D002794:Choline / Q000378:metabolism*; D004848:Epithelium / Q000378:metabolism; D015726:Giant Cells / Q000378:metabolism; D006926:Hymenolepis / Q000378:metabolism*; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D014364:Tryptophan / Q000378:metabolism*
D014364:Tryptophan; D002794:Choline