Studies on soluble proteins released from the synaptic vesicles of rat brain cortex

The effect of morphine tolerance on the incorporation of 3H-leucine into proteins of rat synaptic membranes

The rate of incorporation of 3H-leucine into proteins of the synaptic junctional and nonjunctional membranes and synaptic vesicles of rat brain has been examined in control and morphine-tolerant rats. There are no discernible differences between control and tolerant animals in amount of protein as measured by densitometric tracings of dye-stained proteins separated by acrylamide gel electrophoresis from the three membrane fractions of whole brain areas. However, there are differences in the turnover of membrane protein: three vesicle protein bands and one junctional-membrane protein band are significantly more highly labeled, and one junctional-membrane protein is significantly less highly labeled by 3H-leucine in samples from tolerant rats. Of these, the two junctional-membrane proteins can be tentatively identified as components of the post synaptic densities, and one of the vesicle proteins as tubulin.

A cholinergic modulator

Soluble proteins obtained from presynaptic cholinergic vesicles have been tested regarding their effects to modify postsynaptic spike generation. The results suggest that these proteins (or derivatives, incl. glycopeptides) may act as modulators in increasing the effectiveness and duration of postsynaptic spike generation. They may partake in generation of homosynaptic (posttetanic) potentiation.

Soluble and membrane-bound S-100 protein in cerebral cortex synaptosomes. Properties of the S-100 receptor

Within cerebral cortex synaptosomes, S-100 protein can be recovered in two forms: soluble and membrane-bound. Synaptosomal S-100 is mainly a soluble protein (85 percent). The membrane-bound S-100 is differently distributed in the synaptosomal membranes, intraterminal mitochondria, and synaptic vesicles. S-100 binds to a specific receptor. The binding is time-dependent, reversible and saturable with respect to S-100. The number of receptors is calculated to be about 9 times 10(12)/mg protein, since saturation is achieved at 31 ng [125I]S-100/0.1 mg protein of disrupted synaptosomes. The rate constant for association of S-100 with its receptor at 37 degrees C, k1, is 4.74 times 10(4) M(-1) sec(-1), and the rate constant for dissociation, k-1, 9.24 times 10(-4) sec(-1).

Control of synthesis and release of radioactive acetylcholine in brain slices from the rat. Effects of neurotropic drugs

1. Studies of the synthesis and release of radioactive acetylcholine in rat brain-cortex slices incubated in Locke-bicarbonate-[U-(14)C]glucose media, containing paraoxon as cholinesterase inhibitor, revealed the following phenomena: (a) dependence of K(+)-or protoveratrine-stimulated acetylcholine synthesis and release on the presence of Na(+) and Ca(2+) in the incubation medium, (b) enhanced release of radioactive acetylcholine by substances that promote depolarization at the nerve cell membrane (e.g. high K(+), ouabain, protoveratrine, sodium l-glutamate, high concentration of acetylcholine), (c) failure of acetylcholine synthesis to keep pace with acetylcholine release under certain conditions (e.g. the presence of ouabain or lack of Na(+)). 2. Stimulation by K(+) of radioactive acetylcholine synthesis was directly proportional to the external concentration of Na(+), but some synthesis and release of radioactive acetylcholine occurred in the absence of Na(+) as well as in the absence of Ca(2+). 3. The Na(+) dependence of K(+)-stimulated acetylcholine synthesis was partly due to suppression of choline transport, as addition of small concentrations of choline partly neutralized the effect of Na(+) lack, and partly due to the suppression of the activity of the Na(+) pump. 4. Protoveratrine caused a greatly increased release of radioactive acetylcholine without stimulating total radioactive acetylcholine synthesis. Protoveratrine was ineffective in the absence of Ca(2+) from the incubation medium. It completely blocked K(+) stimulation of acetylcholine synthesis and release. 5. Tetrodotoxin abolished the effects of protoveratrine on acetylcholine release. It had blocking effects (partial or complete) on the action of high K(+), sodium l-glutamate and lack of Ca(2+) on acetylcholine synthesis and release. 6. Unlabelled exogenous acetylcholine did not diminish the content of labelled tissue acetylcholine, derived from labelled glucose, suggesting that no exchange with vesicular acetylcholine took place. In the presence of 4mm-KCl it caused some increase in the release of labelled acetylcholine. 7. The barbiturates (Amytal, pentothal), whilst having no significant effects on labelled acetylcholine synthesis in unstimulated brain except at high concentration (1mm), diminished or abolished (at 0.25 or 0.5mm) the enhanced release of acetylcholine, due to high K(+) or lack of Ca(2+). The fall in tissue content of acetylcholine, due to lack of Ca(2+), was diminished or abolished by pentothal (0.25 or 0.5mm) or Amytal (0.25mm).