Regional distribution and biochemical properties of 125I-Tyr8-substance P binding sites in synaptic vesicles

The study of the conformation and interaction of two tachykinin peptides in membrane mimicking systems by NMR spectroscopy and pulsed field gradient diffusion

Pulsed-field gradient diffusion has been used to study the binding of two tachykinin peptides, [Tyr(8)]-substance P (SP) and [Tyr(0)]-neurokinin A (NKA) to two membrane-mimicking micelles, dodecylphosphocholine, and sodium dodecylsulfate. The structure of these peptides bound to the micelles have also been studied by using two-dimensional nmr and restrained simulated annealing calculations. No major difference in the structures of each peptide in the two micellar media was found. The difference between the micelle-bound structure of [Tyr(8)]SP and that of SP was also minor. The longer helical conformation on the C-terminus for [Tyr(0)]NKA was observed, compared with that for NKA. The relationship between the difference in the biological potencies of [Tyr(8)]SP and SP and the differences in their structure, especially the interaction of the side chains of the two aromatic residues, and the difference in their binding affinities to membrane was discussed. In addition, differences between the result of restrained molecular dynamics simulations of [Tyr(8)]SP in the presence of an explicit micelle and the present results were observed and discussed.

Properties of substance P aggregates. Application to the synthesis and purification of substance P

By 1H-NMR spectroscopy it has been shown that Substance P is largely aggregated at basic and acid pH and in saline solutions. These SP polymers dissociate rapidly by addition of pyridine and acetonitrile and slowly by addition of methanol. The difficulties previously encountered in the purification of SP and SP analogs may be attributed to this aggregation and can be overcome under disaggregating conditions. As a first application of our study we propose a reliable method for obtaining SP with good yield.

Autoradiographic distribution of substance P receptors in rat central nervous system

Among various neuropeptides present in the central nervous system (CNS), substance P, an undecapeptide, is of great interest as a putative pain neurotransmitter. Substance P is present within numerous intrinsic neural pathways throughout the CNS. Several groups have attempted to label substance P receptors on brain membranes by ligand binding techniques; only one study used native 3H-labelled substance P as the ligand and the precise anatomical distribution of substance P receptors has not yet been described. Here we report the autoradiographic localization of 3H-labelled substance P receptors in rat brain using the in vitro autoradiographic technique developed recently. 3H-substance P binds specifically to an apparently single class of sites on slide-mounted brain sections (Kd = 0.52 nM; Bmax = 21.6 fmol per mg protein). The ligand selectivity pattern suggests that 3H-substance P binding sites are similar to those found in other assays. 3H-substance P receptors are highly concentrated in the external layers of the olfactory bulb, medial amygdala, dentate gyrus, superior colliculus, dorsal parabrachial nucleus and locus coeruleus, with moderate densities being found in the nucleus accumbens, striatum, periaqueductal grey and subiculum. The distribution of 3H-substance P receptors suggests that substance P is probably involved in the control of sensory processes such as pain, vision, audition and olfaction.

An enquiry into the mechanism by which substance P facilitates the phasic longitudinal contractions of the rabbit ileum

1. The effect of substance P on the phasic longitudinal contractions of the isolated rabbit ileum has been investigated. The contractions were recorded isotonically. Substance P in concentrations below those which cause tonic contraction (0.2-2 nM) increased the height of the phasic contractions in a concentration-dependent fashion without affecting their frequency (8-12/min).2. The effect of substance P was inhibited by verapamil, ouabain, noradrenaline, and isoprenaline, but was unaffected by tetrodotoxin, atropine, D-2-ala,5-metenkephalin, somatostatin, and vasoactive intestinal polypeptide.3. Tetraethylammonium, which blocks voltage-dependent K(+) channels, enhanced the phasic contractile activity of the rabbit ileum in a manner quite similar to substance P, but the maximal response to tetraethylammonium was larger than that to substance P.4. The effect of matched concentrations of substance P and tetraethylammonium, which enhanced the phasic contractions to a similar extent, was investigated at various concentrations of K(+), Na(+), Ca(2+) and Cl(-) in the bathing medium. Both substance P and tetraethylammonium lost their ability to enhance the phasic contractions when K(+) was omitted from the medium or when its concentration therein was increased by a factor of 4, or when the NaCl concentration was reduced to less than 10%. The relative increase in phasic contractile activity evoked by substance P was smaller than that evoked by tetraethylammonium when more than 90% of the Cl(-) was replaced with propionate.5. Noradrenaline, in a concentration which just abolished the spontaneous phasic contractions (200-300 nM), reduced the enhancing effect of substance P on the phasic activity by 40-50%, but did not influence the effect of tetraethylammonium.6. These results indicate that substance P enhances the phasic longitudinal contractions of the isolated rabbit ileum by a direct action on the smooth muscle cells and that this effect is brought about by facilitation of the myogenically controlled action potential discharges in the ileum. Circumstantial evidence suggests that the underlying ionic mechanism of action of substance P is a decrease in K(+) and Cl(-) conductances.

Further characterization of the binding of substance P to a fraction from rabbit brain enriched in synaptic membranes

1. The present experiments were designed to further characterize the specific [3H]substance P (SP) binding to membrane fractions from rabbit brain. 2. The specific binding was resistant to treatment with proteolytic enzymes whereas phospholipase A(0.7 unit/ml), C(0.025 unit/ml) and D(6.2 unit/ml) reduced the specific binding without decreasing total binding. Neuraminidase (0.01 unit/ml) decreased total binding as well as the specific binding. 3. High concentration of Triton X-100 reduced the specific binding whereas deoxycholate, at 0.05%, reduced both total and the specific binding. 4. Na+ (50--200 mM) reduced the specific binding, depending on the concentrations employed, whereas K+ decreased the specific binding at 10 and 100 mM. The binding was reduced considerably by 100 mmol/l of CaCl2. 5. From these results it is suggested that the specific [3H]SP binding sites in membrane fractions from rabbit brain could be phospholipids.

Specific binding of 3H-substance P to rat brain membranes

The undecapeptide substance P is a putative neurotransmitter in the mammalian central nervous system (CNS), and may be associated with pain fibres in the spinal cord. Radiolabelled derivatives of other neuropeptides have been used to demonstrate specific interactions with receptor sites on brain membranes, and this approach has now been explored with substance P. We have now prepared [4-3H-Phe8]-substance P and we find that it binds reversibly to a saturable population of sites in rat brain particulate fractions. Scatchard analysis of concentration-dependent saturation of binding indicates a single population of non-interacting sites with a high affinity (Kd=0.38 nM) and a low density (Bmax=27.2 fmol per mg protein). Kinetic analyses indicate an apparent dissociation equilibrium constant of 0.46 nM. A variety of neurotransmitter amines and amino acids, and other peptides do not compete at the substance P sites, but structurally related peptides or shorter C-terminal fragments of substance P are active. The rank order of potency of these substance P-related peptides agrees with that reported for their effects in depolarizing spinal cord neurones. The regional distribution of the specific binding sites for 3H-substance P parallels that of substance P immunoreactivity, being high in the hypothalamus and low in the cerebellum and cerebral cortex. The characteristics of the 3H-substance P binding sites are consistent with those expected for substance P receptors.