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Biomedical subjects

C Harding

Publications and source records attributed to C Harding.

33 records · Page 2Linked to original sources
PubMed1985

Morphological analysis of ligand uptake and processing: the role of multivesicular endosomes and CURL in receptor-ligand processing.

The receptor-mediated endocytosis and intracellular processing of transferrin and mannose receptor ligands were investigated in bone marrow-derived macrophages, fibroblasts and reticulocytes. Mannosylated bovine serum albumin (BSA) conjugated to colloidal gold (Au-man-BSA) or colloidal gold-transferrin (AuTf) were used to trace ligand processing in these cells. These ligands appeared to be processed by mechanisms similar to those observed previously with other mannose receptor and galactose receptor ligand probes. After uptake via coated pits and coated vesicles, Au-man-BSA appeared in small uncoated vesicles and tubular structures and was transferred to large, sometimes multivesicular endosomes (MVEs), which sometimes had arm-like protrusions reminiscent of CURL (compartment of uncoupling of receptor and ligand) [10, 11]. Initially these structures became increasingly multivesicular, but during longer incubations the inclusion vesicles appeared to disintegrate to leave a denser, amorphous lumen. Inclusion vesicle disintegration may result from the introduction of lysosomal enzymes into these structures. These results suggest a model for differential receptor-ligand and ligand-ligand sorting. As suggested [10, 11] membrane constituents may be recycled to the plasma membrane from the arms of CURL. Receptor-bound ligands, such as transferrin, would also recycle. The luminal contents, including dissociated ligands, other soluble proteins and inclusion vesicles (containing some membrane proteins), would target to lysosomes. This would result in the lysosomal degradation of any membrane proteins that were incorporated in the inclusion vesicle membranes.

Animals↗
PubMed1984

Hormonal mediation of reproductive behavior.

Reproductive capability requires synchronization of both endocrine and behavioral components of reproduction. The classic view of reproductive behavior was that there was simply direct stimulation of a behavioral response by the appropriate gonadal steroid. However, it has become clear with recent developments in the field of behavioral endocrinology that the relationship of hormonal and behavioral processes is complex. In addition to the complexity of the mechanisms involved, other factors, both social and environmental, influence both the endocrine and behavioral responses. This paper provides an overview of selected issues within the field of behavioral endocrinology which deal with mechanisms of hormonal induction of behavior at various stages of the life cycle and with factors that interact with these processes.

Aging↗
PubMed1984

Endocytosis and intracellular processing of transferrin and colloidal gold-transferrin in rat reticulocytes: demonstration of a pathway for receptor shedding.

Endocytosis and intracellular processing of transferrin (Tf) and Tf receptors were examined in rat reticulocytes. Subcellular fractionation revealed that Tf enters a non-lysosomal endocytic compartment with a density between those of plasma membrane and lysosomes. After 20 min of uptake at (37 degrees C) 35 to 40% of cell-associated Tf was contained in this intermediate-density compartment. To test the fidelity of colloidal gold-Tf (AuTf) as a probe for Tf processing, reticulocytes were fractionated after uptake of 131I-Tf and 125I-AuTf. The subcellular distributions of the two ligands were indistinguishable by this method, a result suggesting that AuTf is processed similarly to Tf. Electron microscopy revealed that AuTf entered multivesicular endosomes (MVEs) as well as various small vesicles and tubular structures. In addition MVE exocytosis was observed with discharge of inclusion vesicles and associated AuTf. AuTf was bound to the outside of these vesicles both before and after exocytosis. These data suggest that Tf receptors are shed from developing reticulocytes by incorporation into the limiting membrane of inclusion vesicles, followed by discharge of these vesicles by MVE exocytosis. As further evidence of this process, we isolated inclusion vesicles after their discharge and found them to contain Tf receptors. Moreover, the rate of Tf receptor shedding by inclusion vesicle discharge matches Tf receptor loss rates closely enough to suggest that this is the primary path of receptor loss during reticulocyte development.

Animals↗
PubMed1983

Transferrin recycling in reticulocytes: pH and iron are important determinants of ligand binding and processing.

Iron uptake by rat reticulocytes is blocked by 20 mM NH4Cl, while 125I-diferric transferrin (Tf) uptake is relatively unaffected. At pH 5.0 both apo- and diferric Tf bind with high affinity; at pH 7.4 diferric Tf binds avidly, but apoTf binds very poorly. The dissociation rate (4 degrees C) of diferric Tf is extraordinarily slow at pH 5.0 (extrapolated t 1/2 = 32 hrs) and faster at pH 7.4 (t 1/2 = 101 min). At pH 5.0 apoTf also dissociates slowly (t 1/2 = 205 min), but at pH 7.4 apoTf exhibits a much faster dissociation rate (t 1/2 = 62 min). 20 mM NH4Cl slows the release of Tf from cells at 37 degrees C, but the rate of externalization of ligand is unaffected. Ligand dissociation at 37 degrees involves both externalization of receptor-ligand complexes and receptor-ligand separation; the NH4Cl effect may result from an increased fraction of externalized Tf in the diferric form which may dissociate more slowly. Receptor-mediated movement of Tf through acid intracellular compartments provides a mechanism to remove iron from Tf and for apoTf to remain receptor-bound for externalization to the cell surface and subsequent dissociation.

Ammonium Chloride↗
PubMed1983

Receptor-mediated endocytosis of transferrin and recycling of the transferrin receptor in rat reticulocytes.

At 4 degrees C transferrin bound to receptors on the reticulocyte plasma membrane, and at 37 degrees C receptor-mediated endocytosis of transferrin occurred. Uptake at 37 degrees C exceeded binding at 4 degrees C by 2.5-fold and saturated after 20-30 min. During uptake at 37 degrees C, bound transferrin was internalized into a trypsin-resistant space. Trypsinization at 4 degrees C destroyed surface receptors, but with subsequent incubation at 37 degrees C, surface receptors rapidly appeared (albeit in reduced numbers), and uptake occurred at a decreased level. After endocytosis, transferrin was released, apparently intact, into the extracellular space. At 37 degrees C colloidal gold-transferrin (AuTf) clustered in coated pits and then appeared inside various intracellular membrane-bounded compartments. Small vesicles and tubules were labeled after short (5-10 min) incubations at 37 degrees C. Larger multivesicular endosomes became heavily labeled after longer (20-35 min) incubations. Multivesicular endosomes apparently fused with the plasma membrane and released their contents by exocytosis. None of these organelles appeared to be lysosomal in nature, and 98% of intracellular AuTf was localized in acid phosphatase-negative compartments. AuTf, like transferrin, was released with subsequent incubation at 37 degrees C. Freeze-dried and freeze-fractured reticulocytes confirmed the distribution of AuTf in reticulocytes and revealed the presence of clathrin-coated patches amidst the spectrin coating the inner surface of the plasma membrane. These data suggest that transferrin is internalized via coated pits and vesicles and demonstrate that transferrin and its receptor are recycled back to the plasma membrane after endocytosis.

Animals↗
PubMed1983

Scanning electron microscopy of X-ray-induced cataract in mice on normal and galactose diet.

The possible multiple effect of galactose diet and X-irradiation on cataract development in mice was investigated by scanning electron microscopy. X-ray cataracts were induced by maintaining animals either on a normal or 50% galactose diet. No detectable changes in lens morphology were seen in animals fed galactose alone compared with normal controls. 2 months after X-ray, less damage had occurred to the lenses of the galactose-fed animals compared to those on a normal diet. At 4 months after X-ray, animals on a normal diet developed mature cataracts, while in the galactose-fed animals they were delayed by 0.5-1.5 months. Suppression of the development of X-ray cataract by galactose feeding may be related to the ability of this sugar, which accumulates in mouse lens due to the low levels of aldose reductase, to act as a free radical scavenger.

Animals↗
PubMed1983

Motor and sensory ulnar nerve conduction velocities: effect of elbow position.

Ulnar motor and sensory nerve conduction velocities (NCV) were studied bilaterally in 20 able-bodied subjects for below elbow (BE) and across elbow (AE) segments to assess the effect of 4 different elbow positions on NCV (0 degrees, 45 degrees, 90 degrees, and 135 degrees). Although constant skin stimulation marker points were used, the AE segment length became progressively longer with increased elbow flexion. At 0 degrees flexion the AE segment motor NCV was found to be slower, and at 45 degrees it was found faster than the BE NCV. At each subsequent elbow flexion position (90 degrees and 135 degrees) there was an erroneous increase in motor and sensory NCV for the AE segments (p less than 0.01). This increase in AE NCV with elbow flexion was mostly due to stretching of skin over the flexed elbow. The nerve itself was observed in 4 cadaver specimens to slide distally with respect to the above elbow skin marker. Since 45 degrees elbow flexion was the position of least variation in motor NCV for AE and BE segments, this degree of elbow flexion appears to be optimum. From these measurements and from literature review neither short AE segment length (less than 10 cm) nor long AE segment length (greater than 15 cm) is optimum for measurement of AE NCV in the assessment of compressive neuropathy at the elbow. Short segments are subject to increased NCV variation while long segments may not detect pathological slowing of NCV only occurring over a short portion of the nerve.

Adult↗
PubMed1980

Androgen affects cholinergic enzymes in syringeal motor neurons and muscle.

We examined the role of testosterone (T) in regulating the weight of the songbird syrinx and the activity of two cholinergic enzymes, choline acetyltransferase (CAT) and acetylcholinesterase (AChE). Castration of adult male zebra finches or neonatal canaries results in a lowering of syringeal weight and CAT and AChE activity. Administration of T for 1-4 weeks restores syringeal weight and AChE to intact levels in male zebra finches. Activity of CAT in muscle is not fully restored. Ovariectomy of female zebra finches and canaries does not affect these syringeal parameters, but T administration to ovariectomized females for 1 month increases syringeal weight and AChE activity. In the zebra finch tracheosyringealis nerve, activity of CAT and AChE is decreased one month after castration. T administration to castrates maintains nerve AChE activity but not CAT. In contrast to changes in the syrinx, tongue muscles do not change in weight or enzyme activity when circulating T levels are altered. Effects of muscle use and disuse were found on syringeal weight and AChE activity, but an androgenic effect also operates in addition. Results suggest that one mechanism for T regulation of singing in passerine birds is through induction of specific enzymatic proteins in androgen target neurons and muscles.

Acetylcholinesterase↗
PubMed1976

The exfoliation syndrome.

A clinical and ultramicroscopic review, including discussion of both scanning and transmission microscopy of the exfoliation syndrome, suggests that the term pseudoexfoliation be replaced by exfoliation syndrome. Involvement of the lens epithelium and, particularly, the pigment epithelium of the iris and the ciliary body epithelium are emphasized as being the likely sources of the exfoliative fibrils. A case of exfoliation syndrome in an eye with an eccentric pupil revealed that the granular material seen on the lens capsule occurs only where the iris is in contact with the lens surface and the process may even involve the central anterior capsule under proper conditions. This finding, together with the evidence of continuing deposits after intracapsular cataract extraction, suggests that the granular material is deposited from the iris and that the material formed by the lens epithelium remains within the lens capsule.

Adult↗
PubMed1968

Sex attractant of sugar beet wireworm: identification and biological activity.

The sex attractant produced by adult females of the sugar beet wire-worm, Limonius californicus (Mannerheim) has been isolated and identified as valeric acid. In the laboratory, male wireworm beetles are repelled by the pure attractant but are drawn with intense sexual excitement to its dilute solutions; in the field, male beetles are lured from a distance of 12 meters. The pheromone occurs in unusually large amounts in the female's body.

Animals↗