No abstract

Pure cholinergic nerve endings (synaptosomes) were isolated from the electric organ of Torpedo by a rapid procedure. These synaptosomes are -3 /zm in diameter. They contain an occasional mitochondrion, numerous synaptic vesicles, and sometimes an active zone is observed. No postsynaptic membrane attachment is found. This nerve ending fraction is extremely pure as shown by morphological controls and biochemical data. It is rich in choline acetyltransferase (450 nmol/h per mg protein) and acetylcholine (ACh) (130 nmol/mg protein). The isolated endings retain their cytoplasmic components and they synthesize ACh and are stable in vitro for several hours, as shown by biochemical measurements and morphological analysis.KEY WORDS synaptosomes acetylcholine 9

Described 40 years ago as cell dust, microparticles (MPs) are now considered a key component in the haemostatic response. Owing to their plasma membrane reactivity, platelets are believed to constitute the main source of circulating procoagulant microparticles and behave as true sensors for the haemostatic response. Erythrocytes, leukocytes and endothelial cells are also able to shed MPs in the blood flow, their respective contribution varying with the pathophysiologic circumstances and extent of the cellular damage. The catalytic properties of MPs rely on a procoagulant anionic phospholipid, phosphatidylserine, made accessible at the outer leaflet following plasma membrane remodelling and on the eventual presence of tissue factor (TF). Under resting conditions, most membrane-bound TF is encrypted. Although able to bind to FVIIa, it does not trigger blood coagulation. Under prothrombotic conditions, TF decryption would occur through intricate pathways involving platelets, monocytes, endothelial cells and derived MPs. P-selectin/P-selectin glycoprotein Ligand-1 (PSGL-1) interactions and reactive oxygen species would promote TF decryption in cell-MP aggregates. At sites of endothelium injury, the swift recruitment of TF+-MPs through P-selectin/PSGL-1 interactions enables the concentration of TF activity above a threshold allowing coagulation to be triggered. Another crucial feature in the initiation of blood coagulation, possibly tuned by MPs, is the balance between TF and TFPI. In specific pathophysiologic contents with elevated levels of circulating TF+-MPs, accessible TFPI at the MP surface would be overwhelmed. Beyond their procoagulant properties demonstrated in vitro, a number of pieces of evidence points to procoagulant MPs as efficient effectors in the haemostatic response, and as pathogenic markers of thrombotic disorders and vascular damage. This review will focus on the pathophysiological significance of platelet-derived MPs and their interaction with vascular cells.

Plasma membrane remodeling characterized by phosphatidylserine exposure and consecutive microparticle (MP) shedding is an ubiquitous process enabling the clearance of senescent cells and the maintenance of tissue homeostasis. MPs are released as fragments from the budding plasma membrane of virtually all eukaryotic cell types undergoing stimulation or apoptosis and may be considered a broad primitive response to stress. MP release is dependent on cytoskeleton degradation pathways involving caspases, requires a sustained increase in intracellular calcium triggering K+ and Cl- efflux and is possibly tuned by mitochondria permeability changes. Because they convey a broad spectrum of bioactive molecules, circulating MPs may serve as shuttles promoting cellular cross talk in various pathological settings such as inflammation or immunity-induced thrombotic disorders. If the drastic shedding of procoagulant MPs appears clearly noxious in thrombotic disorders or in some models of inflammation-induced coagulopathy, this does not necessarily endorse their invariably harmful nature. In the vessel, endothelial cytoprotection reported in the early regulation of inflammation-induced coagulopathy is emblematic of the beneficial effects provided by MPs. In addition, MPs would prove beneficial in the prevention of blood leakage. Because of their multiple properties that are characteristic of a private response of the parental cell, MPs could act as cytoprotective and anti-inflammatory agents through the delivery of activated protein C or annexin 1 and could contribute to the limitation of vascular hyporeactivity. Owing to their ability to cargo bioactive signals, MPs could be viewed as an integrated communication network enabling the coordination of complex cellular responses in biological fluids and the maintenance of the homeostasis equation. A better understanding of the molecular mechanisms involved in MP shedding would pave the way of a new pharmacological approach aiming at the control of MP-driven cellular responses.

The V0 membrane domain of the V-ATPase reversibly dissociates from V1 at acidic intragranular pH and is necessary for normal exocytosis and synaptic transmission.

Procoagulant MP testifying to platelet and endothelial activation are produced in the CSF and in the plasma after severe TBI. A sustained generation of procoagulant MP in the CSF could contribute to a poor clinical outcome.

Pharyngocutaneous fistula after total laryngectomy remains a hardly inevitable complication. The predisposing factors are not clearly identified, but prior radiotherapy seems to increase the risk of fistulae. The purpose of this retrospective study was to determine the value of the pectoralis myofascial flap in pharyngeal reconstruction in post-radiotherapy total laryngectomy in order to decrease the risk of fistula formation. The charts of 60 consecutive patients who had undergone total laryngectomy or pharyngolaryngectomy after radiotherapy were analyzed. Twenty-one variables were recorded for each patient. The overall rate of fistula formation was 38% (23% when a pectoralis myofascial flap was used to cover the pharynx and 50% when no flap was used, P = 0.06). The flap-related complications were exceptional. In the subgroup of patients with diabetes mellitus, a history of vascular disease or a poor nutritional status, the use of a flap reduced the fistula formation from 73 to 13% (P = 0.018). The pectoralis myofascial flap covering the pharyngeal sutures in postradiotherapy laryngectomy is particularly useful in a selected group of patients (with diabetes mellitus, history of vascular disease or poor nutritional status).

Vacuolar H + ATPase (V-ATPase) accumulates protons inside various intracellular organelles, generating the electrochemical proton gradient required for many vital cellular processes. V-ATPase is a complex enzyme with many subunits that are organized into two domains. The membrane domain that translocates protons contains a proteolipid oligomer of several c subunits and a 100 kDa a subunit. Several a-subunit isoforms have been described that are important for tissue specificity and targeting to different membrane compartments, and could also result in the generation of V-ATPases with different functional properties. In the present report, we have cloned the Torpedo marmorata a1 isoform. This isoform was found to be addressed specifically to nerve endings, whereas VATPases in the neuron cell bodies contain a different asubunit isoform. In nerve terminals, the V-ATPase membrane domain is present not only in synaptic vesicles but also in the presynaptic plasma membrane, where its density could reach 200 molecules µm -2 . This V-ATPase interacts with VAMP-2 and with the SNARE complexes involved in synaptic vesicle docking and exocytosis.