A novel nonopioid action of enkephalins: competitive inhibition of the mammalian brain high affinity L-proline transporter.

Published

Journal Article

The high affinity L-proline transporter (PROT) is a member of the family of Na+ (and Cl-)-dependent plasma membrane transport proteins that comprises transporters for several neurotransmitters, osmolytes, and metabolites. The brain-specific expression of PROT in a subset of putative glutamatergic pathways implies a specialized function for this novel transporter and its presumed natural substrate L-proline in excitatory synaptic transmission. However, definitive studies of the physiological role(s) of high affinity L-proline uptake have been precluded by the lack of specific uptake inhibitors. Here, we report that Leu- and Met-enkephalin and their des-tyrosyl derivatives potently and selectively inhibited high affinity L-proline uptake in rat hippocampal synaptosomes and in PROT-transfected HeLa cells. High concentrations of the opiate receptor antagonist naltrexone did not block the inhibitory actions of these peptides, arguing against an involvement of opioid receptors. Des-tyrosyl-Leu-enkephalin elevated the apparent K(m) of L-proline transport in transfected HeLa cells without altering the V(max). PROT-transfected HeLa cells did not accumulate [3H]Leu-enkephalin above background levels, demonstrating that enkephalins are not substrates for PROT. These findings indicate that enkephalins competitively inhibit mammalian brain PROT through a direct interaction with the transporter protein at or near the L-proline binding site. The high potency and specificity of des-tyrosyl-Leu-enkephalin make this compound a useful tool for elucidating the structure-function properties and physiological role(s) of PROT.

Full Text

Duke Authors

Cited Authors

  • Fremeau, RT; Velaz-Faircloth, M; Miller, JW; Henzi, VA; Cohen, SM; Nadler, JV; Shafqat, S; Blakely, RD; Domin, B

Published Date

  • June 1996

Published In

Volume / Issue

  • 49 / 6

Start / End Page

  • 1033 - 1041

PubMed ID

  • 8649341

Pubmed Central ID

  • 8649341

International Standard Serial Number (ISSN)

  • 0026-895X

Language

  • eng

Conference Location

  • United States