Kyotorphin transport and metabolism in rat and mouse neonatal astrocytes

Neuropeptide inactivation is generally thought to occur via peptidase-mediated degradation. However, a recent study found increased analgesia after L-kyotorphin (L-Tyr-L-Arg; L-KTP) administration in mice lacking an oligopeptide transporter, PEPT2. The current study examines the role of PEPT2 in L-KTP uptake by astrocytes and compares it to astrocytic L-KTP degradation. L-[(3)H]KTP uptake was measured in primary cultures of neonatal astrocytes from rats and from Pept2(+/+) and Pept2(-/-) mice. Uptake was further characterized using potential inhibitors. L-[(3)H]KTP degradation was examined in primary astrocyte cultures from Pept2(-/-) mice by following the formation of L-[(3)H]tyrosine. The uptake of L-[(3)H] KTP in both rat and Pept2(+/+) mouse neonatal astrocytes was inhibited by known PEPT2 inhibitors. L-[(3)H]KTP uptake was also reduced in Pept2(-/-) astrocytes as compared to those from Pept2(-/-) mice. Kinetic analysis indicated the presence of a high affinity (K(m) similar to 50 mu M) transporter for L-[(3)H]KTP, identified as Pept2, and a low affinity transporter (K(m) similar to 3-4 mM), inhibited by amastatin, bestatin and tyrosine. Astrocytes also degraded L-KTP through slow affinity peptidase (K(m) similar to 2 mM). Astrocytic clearance of L-KTP occurs via both peptidase activity and transport. These processes occur at similar rates and may be linked. This supports the contention that oligopeptide transport may have an impact on the extracellular clearance (and potentially activity) of certain neuropeptides. (C) 2010 Elsevier B.V. All rights reserved.