Secretory function of the vestibular nerve calyx suggested by presence of vesicles, synapsin I, and synaptophysin

Type I sensory hair cells of the vestibular epithelium are nearly completely ensheathed by an afferent nerve ending, the vestibular nerve calyx. We have recently reported that the nerve calyx, and, in particular, its apical portions surrounding the neck of the hair cell, are immunoreactive for synapsin I (Favre et al., 1986), a major membrane component of small synaptic vesicles of axonal endings. We have now found, by electron microscopy, that the same region of the calyx is densely populated by microvesicles morphologically similar to typical presynaptic small synaptic vesicles. Furthermore, we have established by light microscopy immunocytochemistry that this region of the calyx also contains a high concentration of synaptophysin, another well-characterized major component of small synaptic vesicle membranes. These results suggest that the upper portion of the calyx is equipped with the machinery that in presynaptic terminals is involved in the release of neurotransmitters and raise the possibility that the calyx, via secretion of neurotransmitterlike substances, might modulate the function of type I hair cells.

Synaptophysin (p38) at the frog neuromuscular junction: its incorporation into the axolemma and recycling after intense quantal secretion

Recycling of synaptophysin (p38), a synaptic vesicle integral membrane protein, was studied by the use of antisera raised against the protein purified from frog brain. When frog cutaneous pectoris muscles were fixed at rest, a bright, specific immunofluorescent signal was observed in nerve-terminal regions only if their plasma membranes had been previously permeabilized. When muscles were fixed after they had been treated for 1 h with a low dose of alpha-latrotoxin in Ca2+-free medium, an equally intense fluorescence could be observed without previous permeabilization. Under this condition, alpha-latrotoxin depletes nerve terminals of their quantal store of acetylcholine and of synaptic vesicles. These results indicate that fusion of synaptic vesicles leads to the exposure of intravesicular antigenic determinants of synaptophysin on the outer surface of the axolemma, and provide direct support for the vesicle hypothesis of neurotransmitter release. After 1 h treatment with the same dose of alpha-latrotoxin in the presence of 1.8 mM extracellular Ca2+, immunofluorescent images were obtained only after permeabilization with detergents. Under this condition, the vesicle population was maintained by an active process of recycling and more than two times the initial store of quanta were secreted. Thus, despite the active turnover of synaptic vesicles and of quanta of neurotransmitter, no extensive intermixing occurs between components of the vesicle and presynaptic plasma membrane.

Glutamate uptake by brain synaptic vesicles. Energy dependence of transport and functional reconstitution in proteoliposomes

The dependence of glutamate uptake on ATP-generated proton electrochemical potential was studied in a highly purified preparation of synaptic vesicles from rat brain. At low chloride concentration (4 mM), the proton pump present in synaptic vesicles generated a large membrane potential (inside-positive), associated with only minor acidification. Under these conditions, the rate of L-[3H]glutamate uptake was maximal. In addition, L-glutamate induced acidification of the vesicle interior. D-Glutamate produced only 40% of the effect, and L-aspartate or gamma-aminobutyric acid produced less than 5%. The initial rate of glutamate-induced acidification increased with increasing glutamate concentration. It was saturable and showed first-order kinetics (KM = 0.32 mM). Correspondingly, L-glutamate induced a small reduction in the membrane potential. The rate of ATP hydrolysis was unaffected. In comparison, glutamate had no effect on acidification or membrane potential in resealed membranes of chromaffin granules. At high chloride concentration (150 mM), the vesicular proton pump generated a large pH difference, associated with a small change in membrane potential. Under these conditions, uptake of L-[3H]glutamate by synaptic vesicles was low. For reconstitution, vesicle proteins were solubilized with the detergent sodium cholate, supplemented with brain phospholipids, and incorporated into liposomes. Proton pump and glutamate uptake activities of the proteoliposomes showed properties similar to those of intact vesicles indicating that the carrier was reconstituted in a functionally active form. It is concluded that glutamate uptake by synaptic vesicles is dependent on the membrane potential and that all components required for uptake are integral parts of the vesicle membrane.

Immunohistochemical and ultrastructural localisation of peptide-containing nerves and myocardial cells in the human atrial appendage

The innervation and myocardial cells of the human atrial appendage were investigated by means of immunocytochemical and ultrastructural techniques using both tissue sections and whole mount preparations. A dense innervation of the myocardium, blood vessels and endocardium was revealed with antisera to general neuronal (protein gene product 9.5 and synaptophysin) and Schwann cell markers (S-100). The majority of nerve fibres possessed neuropeptide Y immunoreactivity and were found associated with myocardial cells, around small arteries and arterioles at the adventitial-medial border and forming a plexus in the endocardium. Subpopulations of nerve fibres displayed immunoreactivity for vasoactive intestinal polypeptide, somatostatin, substance P and calcitonin gene-related peptide. In whole-mount preparations of endocardium, substance P and calcitonin gene-related peptide immunoreactivities were found to coexist in the same varicose nerve terminals. Ultrastructural studies revealed the presence of numerous varicose terminals associated with myocardial, vascular smooth muscle and endothelial cells. Neuropeptide Y immunoreactivity was localised to large electron-dense secretory vesicles in nerve terminals which also contained numerous small vesicles. Atrial natriuretic peptide immunoreactivity occurred exclusively in myocardial cells where it was localised to large secretory vesicles. The human atrial appendage comprises a neuroendocrine complex of peptide-containing nerves and myocardial cells producing ANP.

Uptake of GABA by rat brain synaptic vesicles isolated by a new procedure

Uptake of GABA was demonstrated in rat brain synaptic vesicles which were prepared by a new and efficient procedure. The uptake activity co-purified with the synaptic vesicles during the isolation procedure. The purity of the vesicle fraction was rigorously examined by analysis of marker enzymes and marker proteins and also by immunogold electron microscopy using antibodies against p38 (synaptophysin). Contamination by other cellular components was negligible, indicating that GABA uptake by the synaptic vesicle fraction is specific for synaptic vesicles and not due to the presence of other structure possessing GABA uptake or binding activities. GABA uptake was ATP dependent and similar to the uptake of glutamate, which was assayed for a comparison. Both uptake activities were independent of sodium. They were inhibited by the uncoupler carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone, indicating that the energy for the uptake is provided by an electrochemical proton gradient. This gradient is generated by a proton ATPase of the vacuolar type as suggested by the effects of various ATPase inhibitors on neurotransmitter uptake and proton pumping. Competition experiments revealed that the transporters for GABA and glutamate are selective for the respective neurotransmitters.

The synaptic vesicle proteins synapsin I and synaptophysin (protein P38) are concentrated both in efferent and afferent nerve endings of the skeletal muscle

Synapsin I and synaptophysin (protein p38) are 2 major protein components of the membranes of small synaptic vesicles of virtually all presynaptic nerve endings. Synapsin I, a phosphoprotein regulated by both Ca2+ and cAMP, is a peripheral protein of the cytoplasmic surface of the vesicle membrane. It is thought to anchor the vesicle surface to the cytoskeleton of the terminal and to play a regulatory role in neurotransmitter release. Synaptophysin is an intrinsic transmembrane glycoprotein. We report here that both proteins are present and concentrated also in afferent nerve endings, which provide the sensory innervation of the skeletal muscle and of the tendon. The distribution of both antigens in sensory nerve endings is consistent with their localization on the microvesicles that have been described in such endings. Thus, our results suggest the existence of important biochemical, and possibly functional, similarities between small synaptic vesicles of presynaptic nerve endings and microvesicles of sensory endings. Such findings provide new clues to the understanding of the physiology of sensory endings.

Localization of synapsin I at the frog neuromuscular junction

We report here the results of immunocytochemical and biochemical studies on the localization of synapsin I, a nerve terminal--specific phosphoprotein, at the frog neuromuscular junction. Our results show that in this in situ synapse synapsin I is concentrated in the presynaptic compartment, where it appears to be associated with the synaptic vesicle membrane. Double immunoprecipitated synapsin I from homogenates of frog cutaneous pectoris muscles could be phosphorylated by the catalytic subunit of cyclic adenosine 5'-monophosphate-dependent protein kinase after gel electrophoresis and blotting onto nitrocellulose and could be subsequently identified by an immunoperoxidase technique. Experiments carried out in frog brain preparations indicate that frog synapsin I, like the mammalian protein, can be phosphorylated at different sites by exogenously added catalytic subunit of cyclic adenosine 5'-monophosphate-dependent protein kinase and Ca2+/calmodulin-dependent protein kinase II prepared from mammalian sources. The phosphorylation sites of frog synapsin I, as judged by phosphopeptide mapping, are somewhat different from those of mammalian synapsin I. The study of synapsin I and of the regulation of its state of phosphorylation at the neuromuscular junction may provide important information on its role in synaptic function, since at the present time this is one of the few systems in which a correlation among biochemical, immunocytochemical and electrophysiological results is possible.

Quantitation of nerve terminal populations: synaptic vesicle-associated proteins as markers for synaptic density in the rat neostriatum

This study has assessed the contributions of the corticostriatal fibers, the ascending striatopetal fibers, and the intrinsic neostriatal neurons to the nerve terminal population found in the rat neostriatum (caudatoputamen). For this purpose, we have analysed the levels of two different synaptic vesicle-associated proteins, synapsin I and protein p38 (also called synaptophysin), in the neostriatum after specific lesions. Our results indicate that 45-50% of the synaptic vesicle proteins in the rat neostriatum derive from the corticostriatal fibers, that approximately 25-30% of the synaptic vesicle proteins are present in kainic acid-sensitive structures, presumably intrinsic terminals and local collaterals, and that ascending fibers contain 20-25% of the vesicle-associated proteins in the neostriatum. These three neuronal populations therefore comprise 95-100% of the synaptic vesicle-associated proteins in the rat neostriatum, and thus make up most of the nerve terminals in this brain region. The results, which are in general agreement with previous morphometric studies on the rat basal ganglia, therefore indicate that nerve terminals in the central nervous system can be quantitated by use of these biochemical nerve terminal markers. The results also indicate that a somewhat higher percentage of neostriatal nerve terminals belongs to the corticostriatal fibers that previously believed.

Synaptophysin immunoreactivity and small clear vesicles in neuroendocrine cells and related tumours

Synaptophysin (protein p38) immunoreactivity has been detected immunohistochemically in neuroendocrine cells of the human adrenal medulla, carotid body, skin, pituitary, thyroid, lung, pancreas and gastrointestinal mucosa as well as in 87 out of 93 neuroendocrine tumours investigated, including pheochromocytomas, chromaffin and non-chromaffin paragangliomas, ganglioneuromas, pituitary adenomas, thyroid medullary carcinomas, parathyroid adenomas, lung carcinoids and neuroendocrine carcinomas, pancreatic and gut endocrine tumours and cutaneous merkelomas. Parallel ultrastructural investigation of synaptophysin-reactive cells and tumours revealed the presence, in addition to dense-cored, secretory granules, of a population of pleomorphic, small, clear vesicles resembling synaptic vesicles of nerve terminals as well as the synaptophysin immunoreactive vesicles already described in rat adrenal medullary and pituitary cells. Synaptophysin immunoreactivity showed several differences in its distribution among tumour and non-tumour endocrine cells when compared to chromogranin A immunoreactivity, a well known marker of the core of endocrine granules. Synaptophysin represents a reliable general marker of neuroendocrine cells and tumours, which may be useful in diagnostic histopathology.

A synaptic vesicle protein with a novel cytoplasmic domain and four transmembrane regions

Complementary DNA and genomic clones were isolated and sequenced corresponding to rat and human synaptophysin (p38), a major integral membrane protein of synaptic vesicles. The deduced amino acid sequences indicate an evolutionarily highly conserved protein that spans the membrane four times. Both amino and carboxyl termini face the cytoplasm, with the latter containing ten copies of a tyrosine-rich pentapeptide repeat. The structure of synaptophysin suggests that the protein may function as a channel in the synaptic vesicle membrane, with the carboxyl terminus serving as a binding site for cellular factors.

Protein p38: an integral membrane protein specific for small vesicles of neurons and neuroendocrine cells

An intrinsic membrane protein of brain synaptic vesicles with Mr 38,000 (p38, synaptophysin) has recently been partially characterized (Jahn, R., W. Schiebler, C. Ouimet, and P. Greengard, 1985, Proc. Natl. Acad. Sci. USA, 83:4137-4141; Wiedenmann, B., and W. W. Franke, 1985, Cell, 41:1017-1028). We have now studied the presence of p38 in a variety of tissues by light and electron microscopy immunocytochemistry and by immunochemistry. Our results indicate that, within the nervous system, p38, like the neuron-specific phosphoprotein synapsin I, is present in virtually all nerve terminals and is selectively associated with small synaptic vesicles (SSVs). No p38 was detectable on large dense-core vesicles (LDCVs). p38 and synapsin I were found to be present in similar concentrations throughout the brain. Outside the nervous system, p38 was found in a variety of neuroendocrine cells, but not in any other cell type. In neuroendocrine cells p38 was localized on a pleiomorphic population of small, smooth-surfaced vesicles, which were interspersed among secretory granules and concentrated in the Golgi area, but not on the secretory granules themselves. Immunoblot analysis of endocrine tissues and cell lines revealed a band with a mobility slightly different from that of neuronal p38. This difference was attributable to a difference in glycosylation. The finding that p38, like synapsin I, is a component of SSVs of virtually all neurons, but not of LDCVs, supports the idea that SSVs and LDCVs are organelles of two distinct pathways for regulated neuronal secretion. In addition, our results indicate the presence in a variety of neuroendocrine cells of an endomembrane system, which is related to SSVs of neurons but is distinct from secretory granules.

A solid-phase assay for the phosphorylation of proteins blotted on nitrocellulose membrane filters

A new procedure for the phosphorylation and assay of phosphoproteins is described. Proteins are solubilized from tissue samples, separated by polyacrylamide gel electrophoresis, transferred onto nitrocellulose membrane filters, and the blotted polypeptides are phosphorylated with the catalytic subunit of cyclic AMP (adenosine 3':5'-monophosphate)-dependent protein kinase. The method was developed for the assay of dephosphosynapsin I, but it has also proven suitable for the phosphorylation of other proteins. The patterns of phosphorylation of tissue samples phosphorylated using the new method are similar to those obtained using the conventional test tube assay. Once phosphorylated, the adsorbed proteins can be digested with proteases and subjected to phosphopeptide mapping. The phosphorylated blotted proteins can also be analyzed by overlay techniques for the immunological detection of polypeptides.

Applications of hand-arm models in the investigation of the interaction between man and machine

The mode of vibration of hand-held tools cannot be considered without knowledge of the influence of the operator's hand-arm system. Therefore some technical applications of hand-arm models were realized for drill hammers by the University of Dortmund. These applications are a software program to simulate the motion of machine components, a horizontal drilling jig, and a chucking device in a drilling rig.

Characterization of synapsin I binding to small synaptic vesicles

The binding of synapsin I, a synaptic vesicle-associated phosphoprotein, to small synaptic vesicles has been examined. For this study, synapsin I was purified under nondenaturing conditions from rat brain, using the zwitterionic detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS), and characterized. Small synaptic vesicles were purified from rat neocortex by controlled pore glass chromatography as the last purification step, and binding was characterized at an ionic strength equivalent to 40 mM NaCl. After removal of endogenous synapsin I, exogenous dephospho-synapsin I bound with high affinity (Kd, 10 +/- 6 nM) to synaptic vesicles. The binding saturated at 76 +/- 40 micrograms synapsin I/mg of vesicle protein, which corresponded to the amount found endogenously in purified vesicles. Synapsin I binding exhibited a broad pH optimum around pH 7. Other basic proteins, specifically myelin basic protein and histone H2b, did not compete with synapsin I for binding to vesicles. Other membranes purified from rat brain and membranes derived from human erythrocytes did not show the high affinity binding site for synapsin I found in vesicles. The binding of three different forms of phosphosynapsin I to vesicles was investigated. Synapsin I, phosphorylated at sites 2 and 3 by purified calcium/calmodulin-dependent protein kinase II, bound with a 5-fold lower affinity to the vesicles than did dephospho-synapsin I. In contrast, synapsin I, phosphorylated at site 1 by purified catalytic subunit of cAMP-dependent protein kinase, bound with an affinity close to that of dephospho-synapsin I. Synapsin I phosphorylated on all three sites bound to the vesicles with an affinity comparable to that of synapsin I phosphorylated on sites 2 and 3. Under conditions of higher ionic strength (150 mM NaCl equivalent), synapsin I bound with a 5-fold lower affinity to vesicles, and no effect of phosphorylation on binding was observed under these conditions.

A 38,000-dalton membrane protein (p38) present in synaptic vesicles

A protein with an apparent molecular mass of 38,000 daltons designated p38 was found in synaptic vesicles from rat brain. The subcellular distribution of p38 and some of its properties were determined with the aid of polyclonal and monoclonal antibodies. The subcellular distribution of p38 was similar to that of synapsin I, a synaptic-vesicle specific phosphoprotein. p38 in the synaptic vesicle fraction purified by controlled-pore glass bead chromatography showed an enrichment of more than 20-fold over the crude homogenate. Immunostaining of sections through various brain regions revealed an intense labeling of most, and possibly all, nerve terminals. Only faint reaction in the region of the Golgi apparatus and no detectable labeling of axons and dendrites was observed. Two-dimensional electrophoresis revealed that p38 has an acidic pI. Solubilization experiments, as well as phase separation experiments using Triton X-114, indicated that p38 is an integral membrane protein. Binding of antibodies to intact synaptic vesicles, as well as controlled proteolytic digestion of intact and detergent-treated vesicles, revealed that p38 has a domain exposed on the cytoplasmic surface.

Regulation of protein kinases in exocrine secretory cells during agonist-induced exocytosis

Stimulation of exocytosis in exocrine glands is associated with an increased phosphorylation of several particulate proteins. Irrespective of the type of secretagogue (cAMP-dependent agonists, calcium-dependent agonists, calcium ionophores, phorbol esters) exocytosis is always accompanied by an enhanced phosphorylation of the ribosomal protein S6. It is shown by an analysis of the phosphopeptide pattern of the in vivo and the in vitro phosphorylated S6 protein that the protein kinase responsible for phosphorylation of the S6 protein during enhanced exocytosis is protein kinase C. This is so irrespective of whether the agonist uses cAMP or calcium as second messenger. Experiments with isolated guinea pig parotid gland lobules reveal that not only the acetylcholine analog carbamoylcholine, but also the beta-agonist isoproterenol lead within seconds to an increased formation of diacylglycerol. As diacylglycerol increases the affinity of protein kinase C for calcium this finding would explain why the phosphorylation pattern of the S6 protein reflects activation of protein kinase C also under conditions where (as in the case of stimulation with beta-agonists) cAMP is the primary second messenger. It would further explain why the changes of the phosphorylation of individual histones observed during agonist-induced exocytosis in the parotid gland are quite similar for isoproterenol on one hand and carbamoylcholine on the other. A 22 K protein which becomes phosphorylated only when cAMP serves as second messenger is located in the membrane of the endoplasmic reticulum. A possible relationship of this protein with the calcium transport ATPase of the endoplasmic reticulum is under investigation.

[Vascular injury problems in childhood and adolescence]

Because of the marked elasticity of healthy blood vessels in children and adolescents, vascular trauma is very rare. In penetrating injuries, arteriography is not usually necessary but this procedure is essential in cases of blunt trauma to the blood vessels. The type of reconstructive procedure depends on the injury and its extent and can be performed by direct vascular anastomosis, by the insertion of a vein patch or by the transplantation of an autogenic venous segment. General anaesthesia is usually essential. Interrupted one-layer end-to-end anastomosis is advocated. The surgical technique of vascular repair must be meticulous. 12 children and adolescents (most of them had severe multiple injuries including vascular injuries) were followed up clinically and via arteriography. In 11 patients, the reconstructed vessels were found to be functioning normally.

A quantitative dot-immunobinding assay for proteins using nitrocellulose membrane filters

An immunoassay method is described for the quantitative determination of synapsin I (protein I) and of a 36,000-dalton membrane protein from rat brain synaptic vesicles. The samples are spotted on nitrocellulose membrane filters, incubated sequentially with specific antibodies and 125I-labeled protein A, and assayed for radioactivity in a gamma scintillation counter. Conditions have been established to prevent losses of protein from the sheets during processing, to quench background radioactivity, and to adjust the sensitivity to the range desired. A large number of samples can be handled in parallel. The assay does not require iodination of the antigen and is accurate even with crude tissue samples. Standard curves were linear over a 20- to 50-fold range. The sensitivity of the method is such that 10 pmol of synapsin I and 50 ng of total vesicle membrane protein could be measured with accuracy. The method should prove useful for a wide range of proteins.

Specific phosphorylation of a protein in calcium accumulating endoplasmic reticulum from rat parotid glands following stimulation by agonists involving cAMP as second messenger

Stimulation of secretion in exocrine cells by agonists involving cAMP as second messenger is associated with the phosphorylation of a specific membrane-associated 22.4-kDa protein (protein III) (Jahn et al.). Here it is shown by subcellular fractionation of rat parotid gland lobules that protein III is associated with the endoplasmic reticulum. The submicrosomal fractions containing protein III, also contain the ATP-dependent microsomal calcium pump activity. Protein III in microsomal subfractions can be phosphorylated in vitro with catalytic subunit from cAMP-dependent protein kinase. Phosphorylated protein III contains exclusively P-serine. Protein III can be removed from ER-membranes with acid chloroform-methanol or Triton X-114, but not by high salt wash indicating that it is tightly associated with the membranes. Protein III is smaller than phospholamban and, in contrast to phospholamban, resistant to heating in SDS. A relationship between phosphorylation of protein III and microsomal calcium sequestration is discussed.

Phosphopeptide patterns of the ribosomal protein S6 following stimulation of guinea pig parotid glands by secretagogues involving either cAMP or calcium as second messenger

Stimulation of secretion in exocrine cells is associated with the incorporation of up to 3 to 4 phosphates into the ribosomal protein S6. This occurs with secretagogues involving either cAMP or free calcium as second messenger. An analysis of the phosphorylation pattern of S6 from stimulated guinea pig parotid glands reveals 3 phosphopeptides (termed A,B,C). The phosphopeptide pattern was identical for cAMP- or calcium-mediated stimulation, whereas phosphorylation of the S6 protein in vitro with catalytic subunit of cAMP-dependent protein kinase resulted only in the formation of phosphopeptides A and C. Therefore, secretagogue-mediated phosphorylation is not or not exclusively catalyzed by cAMP-dependent protein kinase even when cAMP is the second messenger.