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Biomedical subjects

J E Fox

Publications and source records attributed to J E Fox.

At least 19 recordsLinked to original sources
PubMed1992

Identification of a region in the cytoplasmic domain of the platelet membrane glycoprotein Ib-IX complex that binds to purified actin-binding protein.

The platelet membrane glycoprotein (GP) Ib-IX complex is a major site of attachment of the platelet membrane skeleton to the plasma membrane. This association is mediated by the interaction of actin-binding protein with the GP Ib-IX complex. The aim of the present work was to identify domains on the GP Ib-IX complex that interact with actin-binding protein. Synthetic peptides corresponding to sequences of the GP Ib alpha-chain and beta-chain cytoplasmic domains were analyzed for their ability to bind to purified actin-binding protein. Two overlapping peptides encompassing a sequence (Thr-536-Phe-568) from the central region of the cytoplasmic domain of GP Ib alpha were the most effective in binding 125I-actin-binding protein, as assessed by a microtiter well approach and peptide affinity chromatography. One of the active peptides (Thr-536-Leu-554) was chosen to evaluate the likelihood that the central region of the cytoplasmic domain of GP Ib alpha is involved in binding of the intact complex to actin-binding protein. This peptide could be specifically cross-linked to purified actin-binding protein in solution. Rabbit polyclonal antibody against this peptide inhibited the binding of purified actin-binding protein to the purified GP Ib-IX complex. Finally, as in intact platelets, the calpain-induced hydrolytic fragments of purified actin-binding protein (M(r) = 200,000 and M(r) = 91,000) showed little binding to the GP Ib alpha peptide. Taken together, these results provided evidence that a region between Thr-536 and Phe-568 of the cytoplasmic domain of GP Ib alpha participates in the interaction of the GP Ib-IX complex with actin-binding protein.

Amino Acid Sequence↗
PubMed1992

Efficient plasma membrane expression of a functional platelet glycoprotein Ib-IX complex requires the presence of its three subunits.

The glycoprotein (GP) Ib-IX complex of the platelet plasma membrane mediates the adhesion of platelets to damaged blood vessel wall. The complex is composed of three membrane-spanning polypeptides, GP Ib alpha, GP Ib beta, and GP IX, all of which are absent from the platelets of patients with the hereditary bleeding disorder Bernard-Soulier syndrome. In this study we report stable expression of the recombinant receptor in three cell lines and demonstrate that the three subunits of the complex are necessary for its efficient expression on the plasma membrane. The expressed complex associates with the cytoskeleton of the transfected cells through an interaction with actin-binding protein and binds its ligand, von Willebrand factor. These data suggest that the lack of plasma membrane GP Ib-IX complex in the Bernard-Soulier syndrome could potentially arise from mutations affecting any one of its three subunits.

Animals↗
PubMed1992

Activated phosphoinositide 3-kinase associates with membrane skeleton in thrombin-exposed platelets.

Human platelets undergo a rapid, major reorganization of the cytoskeletal matrix upon exposure to thrombin, and accumulate 3-phosphorylated phosphoinositides in a protein kinase C (PKC)-dependent manner. These phosphoinositides have been suggested to be involved in actin polymerization/depolymerization. We reasoned that, if newly generated 3-phosphorylated phosphoinositide modulates cytoskeletal reorganization, a prerequisite for such action would be generation near cytoskeletal proteins. We have found that, after platelet activation, phosphatidylinositol 3-kinase and phosphatidylinositol(4)P 3-kinase activities, antibody-detectable phosphoinositide 3-kinase, and PKC become markedly and specifically enriched in a Triton X-100-insoluble cytoskeletal fraction that contains GPIIb/IIIa (integrin) and pp60c-src. The cytoskeletal fraction then accounts for up to 70% of total phosphoinositide 3-kinase activity, a function of recruited activated enzyme. These proteins are not occluded or directly associated with newly polymerized actin, since blockage by cytochalasin D of actin polymerization, and consequent inhibition of accumulation of about 40% of incremental protein and actin in this fraction, has no effect on its content of phosphoinositide 3-kinase, GPIIb/IIIa, pp60c-src, or PKC. Depolymerization of actin with DNase I, or inhibition of ligand binding to GPIIb/IIIa by RGDS, however, in combination with cytochalasin D, further depletes actin and significantly decreases sedimentability of GPIIb/IIIa as well as phosphoinositide 3-kinase, pp60c-src, and PKC, without inhibiting total 3-kinase activity. Our results suggest that, as a function of platelet activation, enzymes that regulate the synthesis of 3-phosphorylated phosphoinositides rapidly associate with the membrane skeleton and that skeletally associated phosphoinositide 3-kinase is more active than the Triton-soluble form.

1-Phosphatidylinositol 4-Kinase↗
PubMed1992

Identification of new markers in Xp21 between DXS28 (C7) and DMD.

Characterization of Xp21 distal to Duchenne muscular dystrophy (DMD) in the region containing the genes for adrenal hypoplasia congenita (AHC) and glycerol kinase deficiency (GKD) has been limited due to a paucity of probes. Two probes were localized between DXS28 (C7) and AHC, the yeast artificial chromosome insert YHX39 (DXS727) and the polymorphic phage clone QST59 (DXS319). A genomic clone, FT1 (DXS726), 3' to DMD, was also characterized. Portions of the three probes were sequenced and primer pairs were generated to amplify a sequence-tagged site within each probe. Amplification of DNA from patients confirmed the deletion results obtained by Southern blot analysis, and these three sequence-tagged sites were successfully combined for triplex PCR. In addition to facilitating molecular genetic diagnosis in Xp21, these probes can be used to identify additional YACs and other probes to further increase the genomic information and diagnostic capabilities in this region.

Base Sequence↗
PubMed1979

Subcellular distribution of the different platelet proteins phosphorylated on exposure of intact platelets to ionophore A23187 or to prostaglandin E1. Possible role of a membrane phosphopolypeptide in the regulation of calcium-ion transport.

Exposure of 32P-labelled human platelets to ionophore A23187 results in an increased incorporation of 32P into polypeptides with apparent mol.wts. of 47 000 (P47) and 20 000 (P20), whereas exposure to prostaglandin E1 results in increased labelling of polypeptides with apparent mol.wts. of 24 000 (P24) and 22 000 (P22) [Haslam, Lynham & Fox (1979) Biochem. J. 178, 397-406]. Labelled platelets that had been incubated with ionophore A23187 or prostaglandin E1 were sonicated and rapidly separated into three fractions by differential centrifugation. Electron microscopy and measurement of marker enzymes indicated that the 1300-19 000 gav. particulate fraction was enriched in granules, mitochondria and plasma membranes, that the 19 000-90 000 gav. particulate fraction was enriched in both intracellular and plasma membranes and that the 90 000 gav. supernatant contained only soluble proteins. 32P-labelled phosphopolypeptide P47 was present almost exclusively in the 90 000 gav. supernatant, whereas phosphopolypeptide P20 was largely dephosphorylated under fractionation conditions that protected other phosphopolypeptides. 32P-labelled phosphopolypeptide P24 was enriched in both particulate fractions, but particularly in the 19 000-90 000 gav. fraction, and may therefore be present in both the intracellular and plasma membranes. Phosphopolypeptide P22 appeared to be similarly distributed. Both particulate fractions were capable of the ATP-dependent oxalate-stimulated uptake of Ca2+. When the 19 000-90 000 gav. membrane fraction was prepared from platelets that had been incubated with ionophore A23187, active uptake of Ca2+ did not occur, but when this fraction was isolated from platelets that had been exposed to prostaglandin E1, uptake of Ca2+ was significantly greater than observed with the corresponding membranes from control platelets. It is suggested that phosphorylation of polypeptide P24 (or P22) by a cyclic AMP-dependent protein kinase may promote the active transport of Ca2+ out of the platelet cytosol.

Anti-Bacterial Agents↗
PubMed1979

Effects of collagen, ionophore A23187 and prostaglandin E1 on the phosphorylation of specific proteins in blood platelets.

Human platelets that had been preincubated with 5-hydroxy[(3)H]tryptamine and [(32)P]P(i) were stirred with various agents; the secretion of 5-hydroxy[(3)H]tryptamine from platelet granules and the radioactivity of platelet [(32)P]phosphopolypeptides separated by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis were then measured. Exposure of the platelets to collagen fibres or ionophore A23187 selectively increased the phosphorylation of polypeptides with apparent mol.wts. of 47000 (P47) and 20000 (P20) by approx. 3-fold, in association with the release of 5-hydroxy[(3)H]tryptamine. The 47000-mol.wt. phosphopolypeptide (P47) was clearly separated from platelet actin by the electrophoresis system used. Prostaglandin E(1), which inhibits platelet function by increasing platelet cyclic AMP, decreased the phosphorylation of polypeptides caused by collagen as well as the release of 5-hydroxy[(3)H]tryptamine. Prostaglandin E(1) also selectively increased the phosphorylation of distinct polypeptides with apparent mol.wts. of 24000 (P24) and 22000 (P22) by approx. 2-fold. As the phosphorylation reactions caused by collagen are probably mediated by an increase in Ca(2+) concentration in the platelet cytosol and may have a role in the release reaction [Haslam & Lynham (1977) Biochem. Biophys. Res. Commun.77, 714-722; (1978) Thromb. Res.12, 619-628], we suggest that a cyclic AMP-dependent phosphorylation of the 24000- and/or 22000-mol.wt. polypeptides caused by prostaglandin E(1) may initiate processes that decrease the Ca(2+) concentration in the cytosol, so inhibiting both the Ca(2+)-dependent phosphorylation reactions and the release reaction. Treatment of platelets with prostaglandin E(1) did not inhibit the increased phosphorylation of polypeptides with apparent mol.wts. of 47000 and 20000 (P47 and P20) caused by ionophore A23187, which may therefore short-circuit cyclic AMP-dependent mechanisms that decrease the Ca(2+) concentration in the platelet cytosol. As prostaglandin E(1) did inhibit the release of 5-hydroxy[(3)H]tryptamine by ionophore A23187, cyclic AMP may also inhibit the release reaction by additional mechanisms.

Anti-Bacterial Agents↗
PubMed1979

The ultrastructure of blebs induced in the hamster jejunum by ethanol.

Previous light microscopic studies showed that perfusion of the hamster jejunum with 4.8% ethanol (ethanol period) in vivo produced fluid-filled subepithelial blisters (blebs) on the villi. These blebs had virtually disappeared within 45 min after the discontinuation of the ethanol perfusion (recovery period). The present study examined these ethanol-induced changes in the jejunum by scanning (SEM) and transmission (TEM) electron microscopy. TEM revealed that ethanol did not damage epithelial cells in areas where blebs were not present. In these areas the basal surfaces of the epithelial cells were attached to the basal lamina, and the lateral intercellular spaces (LIS) were open. In the areas where blebs formed, the stretched epithelial cells which covered the blebs lost their basal anchoring and so could not maintain their LIS. Both SEM and TEM indicate that there was a decrease in the quantity of glycocalyx at the surfaces of cells which covered blebs. Our findings indicate that ethanol does not directly damage epithelial cells but that the cellular damage is due to detachment over the blebs. It is likely that ethanol at first traverses the epithelial layer and then produces stasis in the villus core. Continued fluid transport by the epithelial layer in the presence of statis results in accumulation of the fluid and widely dilated LIS. With subsequent enlargement of the LIS the bases of the cells detach from the basal lamina and blebs are formed.

Animals↗
PubMed1978

Cyclic nucleotides in platelet function.

Inhibition of adenylate cyclase in intact platelets by addition of compounds such as 2', 5' - dideoxyadenosine prevented the inhibition of platelet aggregation by PGE1 but did not affect the responses of platelets to aggregating agents in the absence of PGE1. This confirms that cyclic AMP mediates the effects of PGE1 but indicates that the level of cyclic AMP in unstimulated platelets is too low to affect the actions of aggregating agents. Studies on the phosphorylation of proteins in intact 32P-labelled platelets showed that PGE1 increased the phosphorylation of a membrane-bound polypeptide (P24) and prevented the increased phosphorylation of other polypeptides (P47 and P20) that occurred on addition of inducers of the release reaction. It is suggested that the cyclic AMP-dependent phosphorylation of P24 stimulates the active transport of Ca(2+) out of the platelet cytosol, so preventing phosphorylation of P47 and P20, reactions which may be involved in the release mechanism. As increases in platelet cyclic GMP could be dissociated from both platelet aggregation and the release reaction, it is proposed that the bidirectional regulation of platelet function is achieved primarily by the opposing actions of increases in the concentrations of Ca(2+) and cyclic AMP.

Blood Platelets↗
PubMed1978

Effect of ethanol on glucose and water absorption in hamster jejunum in vivo. Methodological problems: anesthesia, nonabsorbable markers, and osmotic effect.

We studied the effect of ethanol on glucose and water absorption in vivo. In preliminary experiments, using sodium amytal anesthesia, we found that control animals, whose jejunal segment was perfused without ethanol, required more anesthetic agent than those perfused with ethanol. Thus, to allow for unbiased comparison of the absorption data between the two groups of animals, all absorption studies were carried out on conscious restrained hamsters. We found that ethanol did not influence the permeability of the jejunum to polyethylene glycol (PEG) and meglumine diatrizoate. In addition, ethanol did not influence the time required for the onset of steady-state absorption. Using both the gravimetric and the electrical methods, we were unable to show any measurable osmotic pressure exerted by ethanol (150-1050 mM) on the hamster jejunum. In the absorption studies we found that perfusion of the hamster jejunum with five increasing concentration of ethanol (450-1050 mM) appeared to cause a concentration-dependent depression in steady-state glucose transport. Water transport was depressed only when 4.8% (1050 mM) ethanol was perfused.

Alcoholic Intoxication↗
PubMed1978

Effect of ethanol on the morphology of hamster jejunum.

In order to study the morphological effects of exposure of the jejunum to low ethanol concentrations, we perfused hamster jejunum with 2.1-4.8% ethanol. Following 45 min exposure, many of the villi developed fluid-filled blisters. To compare these findings to the effect of an inert solute at similar concentrations, we perfused hamster jejuna with mannitol. This caused necrosis of the villus tips but no blister formation. Therefore the blisters were the result of the action of ethanol. The rat jejunum was less resistant to ethanol than that of the hamster. We suggest that the initial insult of the freely permeant ethanol is deep to the epithelium, resulting in accumulation of edema under the epithelium.

Alcoholic Intoxication↗
PubMed1978

Excitatory and inhibitory components of the eyeblink responses to startle evoking stimuli, studied in the human subject.

Integrated EMG recordings have been used to study the eyeblink component of the human startle reflex. They have shown that the response, to either an auditory or a painful stimulus, consists of an initial excitation followed by a more prolonged period during which a second stimulus, of the same or different sensory modality, fails to evoke a response, or evokes one which is reduced in amplitude. The period of reduced responsiveness does not follow voluntary or spontaneous eyeblinks. Increasing the duration of the startle evoking stimulus has little effect on the excitatory component of the response, but prolongs the subsequent period of reduced responsiveness. When stimuli of one modality are presented repetitively to the subject, the eyeblink response is habituated; the response to a subsequent testing stimulus, of a different sensory modality, is then smaller than that evoked by the testing stimulus alone, but greater than that evoked by the testing stimulus when it follows a single conditioning stimulus. It is concluded that the excitatory and inhibitory components of the startle reflex are at least partially separable and that stimulus novelty has some significance in eliciting a response.

Acoustic Stimulation↗
PubMed1978

The correlation of ethanol-induced depression of glucose and water transport with morphological changes in the hamster jejunum in vivo.

Glucose and water transport is depressed in the hamster jejunum in vivo by ethanol (4.8%) which also produced fluid-filled blebs at the tips of the villi. The epithelial cells over the blebs appeared stretched and cuboidal, the lateral intercellular spaces (LIS) were no longer recognizable, and the lacteals were closed. Forty-five minutes after discontinuation of the ethanol, water transport returned to normal while glucose transport remained depressed. At this time the villus structure had returned to normal. The blebs had disappeared, the LIS were again recognizable, and their appearance and number were similar to those in the control animals. Thus, the depression of water transport correlated with the obvious structural changes caused by ethanol; however, the depression of glucose absorption is associated with some effect of ethanol not evident by routine light microscopy.

Animals↗
PubMed1978

Bovine coccidiosis. A review, including field safety studies with decoquinate for prevention.

Decoquinate (Deccox: Hess & Clark) has been demonstrated in in-house and university studies to be an active coccidiostat when fed daily at 0.5 mg/kg body weight during periods of oocyst exposure, or when experience indicates coccidiosis is likely to be a hazard. For prevention, feeding should be continued for at least 28 days. In 6 feedlot trials with 1993 cattle in 5 geographic areas, decoquinate fed at this level for 90-120 days had no adverse effects. In 5 of these trials, treated cattle had equal or slightly improved average daily gains and feed conversion by comparison with controls.

Animals↗