Active uptake system for substance P carboxy-terminal heptapeptide (5-11) into a fraction from rabbit enriched in glial cells. 
In the present study, we demonstrated the existence of an active uptake system for substance P carboxy-terminal heptapeptide, (5-11)SP.  When a fraction from rabbit brain enriched in glial cells was incubated with [3H] (5-11)SP, an uptake of [3H](5-11)SP was observed.  The uptake system has the properties of an active transport mechanism.  Kinetic analysis indicated two components of [3H](5-11)SP uptake, one representing a high and the other a low affinity transport system.  After unilateral ablation of the striatum, approximately 30% of the high affinity [3H](5-11)SP uptake capacity of substantia nigra slices disappeared.  The subcellular distribution of the high affinity uptake indicated that [3H] 5-hydroxytryptamine was taken up mostly into the P2B fraction (synaptosomal fraction), whereas [3H](5-11)SP was taken up into the P2A fraction (myelin fraction) to the same extent as into the P2B fraction.  These results suggest that when SP is released from nerve terminals, it is hydrolysed into (5-11)SP, which is in turn accumulated into glial cells as well as nerve terminals and that this high affinity uptake mechanism may play an important role in terminating the synaptic action of SP.