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Biomedical subjects

J E Fox

Publications and source records attributed to J E Fox.

At least 127 records · Page 7Linked to original sources
PubMed1985

Biosynthesis and Degradation of a Wheat Embryo Cytokinin-Binding Protein during Embryogenesis and Germination.

The accumulation and degradation of a wheat (Triticum durum) embryo cytokinin-binding protein (CBF-1) was followed during embryo development and germination by its N(6)-benzyladenine (BA) binding activity and immunological reactivity (rocket immunoelectrophoresis and Western blotting). Both BA binding activity and CBF-1 appeared at 2 weeks post-anthesis and rose sharply between 2 to 4 weeks before leveling off to approximately 47 micrograms per embryo (9% of the soluble embryo protein at maturity). In vitro translation of polyadenylated RNA from 20-day-old embryos yielded a polypeptide which was immunoprecipitable with anti-CBF-1 IgG and migrated closely to the 54-kilodalton CBF-1 polypeptide on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Upon germination, both the amount of CBF-1 and BA binding activity dropped to low levels within 3 days. The data are discussed in relation to the possible role of CBF-1 as a regulator of cytokinin availability, and comparisons are drawn between the structural and biosynthetic similarities found between CBF-1 and the vicilin storage proteins of legumes. An improved method for isolating undegraded CBF-1 from whole seeds is also presented.

Journal Article↗
PubMed1985

Muscarinic inhibition of canine small intestinal motility in vivo.

The quiescent canine gastrointestinal tract responsed to close intraarterial acetylcholine with an atropine-sensitive, hexamethonium, and tetrodotoxin-insensitive contraction, thus suggesting acetylcholine interacts with a muscarinic receptor located on the muscle. When the gut is actively contracting (spontaneously, in response to field stimulation or to motilin), acetylcholine caused a contraction followed by prolonged inhibition of contractions. No such inhibition was apparent after tetrodotoxin; therefore, the receptor for acetylcholine-induced inhibition was apparently on nerves. Neither the acetylcholine-induced excitation nor the inhibition was altered by hexamethonium or reserpine treatment. Both inhibitory and excitatory responses were greatly reduced by atropine, suggesting that both receptors were muscarinic in nature. McNeil A343 produced inhibition but no excitation. Tetrodotoxin, hexamethonium, reserpine, and pirenzepine all increased the concentration of McNeil A343 required for production of 50% inhibition, suggesting it acts via multiple mechanisms. Furthermore, pirenzepine reduced both the inhibitory and excitatory response to acetylcholine, suggesting that it is nonselective in its action on the neural inhibitory or muscular excitatory receptors. We suggest that the presynaptic muscarinic receptor responsible for inhibitory effects of acetylcholine is on the postganglionic cholinergic neuron itself and constitutes an important negative-feedback loop to reduce excessive cholinergic output. Although such a mechanism has been found in vitro previously, this is the first report in vivo in canine small intestine.

(4-(m-Chlorophenylcarbamoyloxy)-2-butynyl)trimethy↗
PubMed1985

Linkage of a membrane skeleton to integral membrane glycoproteins in human platelets. Identification of one of the glycoproteins as glycoprotein Ib.

Experiments were performed to determine whether platelets contain a membrane skeleton. Platelets were labeled by a sodium periodate/sodium [3H]borohydride method and lysed with Triton X-100. Much of the filamentous actin could be sedimented at low g forces (15,600 g, 4 min), but some of the actin filaments required high-speed centrifugation for their sedimentation (100,000 g, 3 h). The latter filaments differed from those in the low-speed pellet in that they could not be depolymerized by Ca2+ and could not be sedimented at low g forces even from Triton X-100 lysates of platelets that had been activated with thrombin. Actin-binding protein sedimented with both types of filaments, but 3H-labeled membrane glycoproteins were recovered mainly with the high-speed filaments. The primary 3H-labeled glycoprotein recovered with this "membrane skeleton" was glycoprotein (GP) Ib. Approximately 70% of the platelet GP Ib was present in this skeleton. Several other minor glycoproteins, including greater than 50% of the GP Ia and small amounts of three unidentified glycoproteins of Mr greater than 200,000, were also recovered with the membrane skeleton. The Triton X-100 insolubility of GP Ib, GP Ia, a minor membrane glycoprotein of 250,000 Mr, and actin-binding protein resulted from their association with actin filaments as they were rendered Triton X-100-soluble when actin filaments were depolymerized with deoxyribonuclease I and co-isolated with actin filaments on sucrose gradients. When isolated platelet plasma membranes were extracted with Triton X-100, actin, actin-binding protein, and GP Ib were recovered as the Triton X-100 residue. These studies show that unstimulated platelets contain a membrane skeleton composed of actin filaments and actin-binding protein that is distinct from the rest of the cytoskeleton and is attached to GP Ib, GP Ia, and a minor glycoprotein of 250,000 Mr on the plasma membrane.

Actin Cytoskeleton↗
PubMed1984

Motor effects of gastrin releasing peptide (GRP) and bombesin in the canine stomach and small intestine.

Close intraarterial injections of synthetic porcine gastrin releasing peptide (GRP) or bombesin stimulated contractions in the stomach and inhibited ongoing contractile activity in the small intestine of anaesthetized dogs. Contractile activity of the circular muscle was recorded by serosal strain gauges and phasic activity when desired was elicited by local field stimulation or intraarterial motilin injections. In the stomach (corpus and antrum) following tetrodotoxin blockade of field-stimulated contractions, the contractile response to either peptide was not present, suggesting that stimulation of receptors on nerves initiated contractions in the stomach. Similarly, in the small intestine, the inhibitory response was eliminated by tetrodotoxin suggesting a neural receptor. Pre-treatment with reserpine did not alter the inhibitory response, either in the presence or absence of atropine, therefore, adrenergic inhibitory mechanisms did not appear to be involved. The concentration of bombesin producing 50% inhibition of field stimulation (ED50) was increased following treatment with the putative M1 muscarinic antagonist, pirenzipine suggesting activation of M1 cholinergic inhibitory receptors by bombesin. After blockade by atropine of field-stimulated contractions and the contractile response to intraarterial acetylcholine, the ED50 for bombesin inhibition of motilin contractions was increased. After muscarinic blockade, the residual inhibitory response of GRP/bombesin may involve activation of a neural non-cholinergic non-adrenergic inhibitory mechanism. These results suggest that GRP and bombesin act to alter motility in the dog in vivo by affecting neural activity.

Animals↗
PubMed1984

Effects of porcine gastrin releasing peptide (GRP) on canine antral motility and gastrin release in vivo.

The effect of GRP on the in vivo canine antrum was investigated. GRP caused a dose-dependent increase in antral gastrin output which was not significantly altered by administration of tetrodotoxin. The higher doses of GRP administered also caused excitation of antral motility which was abolished by tetrodotoxin, a finding in contrast to previous in vitro results demonstrating bombesin-induced antral smooth muscle contraction to be tetrodotoxin-resistant. These data suggest that in the in vivo canine model GRP causes antral gastrin release via non-neurally mediated mechanisms (probably by acting directly on the G-cell) and excites antral motility via neurally-mediated mechanisms.

Animals↗
PubMed1984

Motilin--an update.

Motilin isolated in 1971 from the porcine gastrointestinal tract and localized there to endocrine cells, now appears to have a CNS neural origin by RIA and immunohistochemistry. In most species motilin releases neurotransmitters in the CNS to both increase and decrease neural transmission and in the gastrointestinal tract to increase motor activity. In the fasting animal, motilin initiates premature activity fronts of the migrating motor complex (MMC) in the upper gastrointestinal tract by an atropine or tetrodotoxin-sensitive mechanism. Immunoreactive motilin-release from the gut can be correlated with the passage of these fronts through the upper gut. In the dog, the associated events of this MMC, i.e. motor activity of the duodenum extrinsic and intrinsic neural activity and emptying of biliary and pancreatic secretions into the duodenum, all appear to contribute to the peaks in peripheral plasma immunoreactive motilin concentrations. In man, there appears to be a close association of motilin secretion with biliary and pancreatic secretions being emptied into the duodenum and less evidence for motor activity releasing motilin. Only in the dog is there strong evidence for an absolute requirement of motilin for the consolidation of the motor activity of the upper gut into the MMC. In man, the evidence is less convincing although motilin may facilitate the process and in the pig, motilin appears to have little or no role in MMC generation. No pathological consequences of hypermotilemia have been described although elevated motilin levels have been found to be associated with some diarrheal states, renal failure, and in the first week following abdominal surgery. Motilin thus remains a hormone seeking a physiological function in some species and a pathological role in all species.

Animals↗