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Biomedical subjects

A Entwistle

Publications and source records attributed to A Entwistle.

25 records · Page 2Linked to original sources
PubMed1989

Protein kinase C mediates the hormonally regulated plasma membrane fusion of avian embryonic skeletal muscle.

Recent findings have demonstrated that prostanoid-generated calcium fluxes can trigger myoblast fusion and suggest inositol phospholipid turnover as part of the fusion mechanism. Here we demonstrate that a block imposed on myoblast fusion by antagonists of prostanoid biosynthesis can be overcome by either the membrane-permeable diacylglycerol, 1-oleoyl-2-acetyl-sn-glycerol (OAG), or 12-O-tetradecanoylphorbol 13-acetate (TPA). Both phorbol and the membrane-impermeable dioleoylglycerol were ineffective. These results implicate protein kinase C activation in prostaglandin E1-mediated myoblast fusion and add weight to the contention that inositol turnover is involved in the regulation of myoblast fusion.

Alprostadil↗
PubMed1988

The control of chick myoblast fusion by ion channels operated by prostaglandins and acetylcholine.

Chick myoblast fusion in culture was investigated using prostanoid synthesis inhibitors to delay spontaneous fusion. During this delay myoblast fusion could be induced by prostaglandin E1 (PGE1), by raising extracellular potassium and by addition of carbachol. Carbachol-induced fusion, but not PGE-induced fusion, was prevented by the acetylcholine receptor blocker alpha-bungarotoxin. Fusion induced by any of these agents was prevented by the Ca channel blockers lanthanum and D600. The threshold for potassium-induced fusion was 7-8 mM; maximal fusion occurred at 16-20 mM. Low extracellular potassium inhibited spontaneous fusion. Intracellular potassium in fusion competent myoblasts was 101 m-moles/l cell. Calcium flux measurements demonstrated that high potassium increased calcium permeability in fusion-competent myoblasts. A 30-s exposure to high potassium or PGE1 was sufficient to initiate myoblast fusion. Anion-exchange inhibitors (SITS and DIDS) delayed spontaneous myoblast fusion and blocked fusion induced by PGE1 but not carbachol. Blocking the acetylcholine receptor shifted the dose-response relation for PGE-induced fusion to higher concentrations. PGE1-induced fusion required chloride ions; carbachol-induced fusion required sodium ions. Provided calcium channels were available, potassium always induced fusion. We conclude that myoblasts possess at least three, independent pathways, each of which can initiate myoblast fusion and that the PGE-activated pathway and the acetylcholine receptor-activated pathway act synergistically. We suggest that fusion competent myoblasts have a high resting membrane potential and that fusion is controlled by depolarization initiated directly (potassium), by an increase in permeability to chloride ions (PGE), or by activation of the acetylcholine receptor (carbachol); depolarization triggers a rise in calcium permeability. The consequent increase in intracellular calcium initiates myoblast fusion.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1988

A role for acetylcholine receptors in the fusion of chick myoblasts.

The role of acetylcholine receptors in the control of chick myoblast fusion in culture has been explored. Spontaneous fusion of myoblasts was inhibited by the nicotinic acetylcholine receptor antagonists alpha-bungarotoxin, Naja naja toxin and monoclonal antibody mcAb 5.5. The muscarinic antagonists QNB and n-methyl scopolamine were without effect. Atropine had no effect below 1 microM, where it blocks muscarinic receptors; at higher concentrations, when it blocks nicotinic receptors also, atropine inhibited myoblast fusion. The inhibitions imposed by acetylcholine receptor antagonists lasted for approximately 12 h; fusion stimulated by other endogenous substances then took over. The inhibition was limited to myoblast fusion. The increases in cell number, DNA content, the level of creatine phosphokinase activity (both total and muscle-specific isozyme) and the appearance of heavy chain myosin, which accompany muscle differentiation, followed a normal time course. Pre-fusion myoblasts, fusing myoblasts, and young myotubes specifically bound labeled alpha-bungarotoxin, indicating the presence of acetylcholine receptors. The nicotinic acetylcholine receptor agonist, carbachol, induced uptake of [14C]Guanidinium through the acetylcholine receptor. Myoblasts, aligned myoblasts and young myotubes expressed the synthetic enzyme Choline acetyltransferase and stained positively with antibodies against acetylcholine. The appearance of ChAT activity in myogenic cultures was prevented by treatment with BUDR; nonmyogenic cells in the cultures expressed ChAT at a level which was too low to account for the activity in myogenic cultures. We conclude that activation of the nicotinic acetylcholine receptor is part of the mechanism controlling spontaneous myoblast fusion and that myoblasts synthesize an endogenous, fusion-inducing agent that activates the nicotinic ACh receptor.

Animals↗
PubMed1986

Myoblast fusion is regulated by a prostanoid of the one series independently of a rise in cyclic AMP.

The role of prostanoids in the regulation of chick myoblast differentiation has been investigated. At 3 X 10(-6) M, indomethacin and chloroquine specifically inhibit cell fusion. They do not affect cell proliferation, alignment, or the expression of two muscle-specific proteins, namely, the acetylcholine receptor and the muscle-specific form of creatine phosphokinase. The results demonstrate that it is indomethacin's activity as an inhibitor of prostaglandin synthesis at the cyclooxygenase step that causes the block of cell fusion, whereas chloroquine probably acts at the earlier step of phospholipase A. Prostaglandin E1 (PGE1), but not prostaglandin E2 (PGE2), rapidly reverses the inhibition of fusion imposed by indomethacin or chloroquine. The dose response of the myoblasts to PGE1 is a bell-shaped curve with a 100% reversal of fusion at approximately 10(-9) M. Eicosatrienoate and linoleate reverse the inhibition of fusion with similar kinetics, whereas arachidonate is completely ineffective. The ability of PGE1 and eicosatrienoate but not PGE2 and arachidonate to restore fusion to control levels implies that fusion is specifically regulated by a prostanoid of the one series. The reversal of the fusion-block by linoleate further suggests that this fatty acid provides the necessary source of eicosatrienoate in the myoblast plasma membrane. At 10(-8) M and above, PGE1 and PGE2 stimulate adenylate cyclase and depress control fusion as does 10(-5) M isoproterenol. The beta-adrenergic blocker propranolol abolishes both isoproterenol's inhibition of myoblast fusion and its activation of adenylate cyclase. The similar depressions imposed on cell fusion by 10(-8)-10(-6) M prostanoid and 10(-5) M isoproterenol suggest that in both cases the depressive effects are mediated by cyclic AMP. It is concluded that a prostanoid of the one series regulates fusion by a cyclic AMP-independent mechanisms.

Alprostadil↗
PubMedDate not supplied

The microanatomy of the alveolar duct of the human lung imaged by confocal microscopy and visualised with computer-based 3D reconstruction.

The most widely accepted model of human lung alveolar duct systems is that they are constructed from central helical fibres between the turns of which lie alveolar opening. Experimental difficulties of handling and sectioning lung tissue have made it difficult to confirm this. Confocal laser scanning microscopy (CLSM) was therefore used to generate optical serial sections of the lung that were reconstructed in three dimensions and displayed using volume rendering techniques. From images of the reconstructions, a new structure is proposed in which alveolar ducts consist of collections of connected oval, twisted loop structures with eccentric openings.

Adult↗
PubMedDate not supplied

Sharing digital micrographs and other data files between computers.

It ought to be easy to exchange digital micrographs and other computer data files with a colleague even on another continent. In practice, this often is not the case. The advantages and disadvantages of various methods that are available for exchanging data files between computers are discussed. When possible, data should be transferred through computer networking. When data are to be exchanged locally between computers with similar operating systems, the use of a local area network is recommended. For computers in commercial or academic environments that have dissimilar operating systems or are more widely spaced, the use of FTPs is recommended. Failing this, posting the data on a website and transferring by hypertext transfer protocol is suggested. If peer to peer exchange between computers in domestic environments is needed, the use of Messenger services such as Microsoft Messenger or Yahoo Messenger is the method of choice. When it is not possible to transfer the data files over the internet, single use, writable CD ROMs are the best media for transferring data. If for some reason this is not possible, DVD-R/RW, DVD+R/RW, 100 MB ZIP disks and USB flash media are potentially useful media for exchanging data files.

Computer Communication Networks↗