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Biomedical subjects

L W Haynes

Publications and source records attributed to L W Haynes.

69 records · Page 4Linked to original sources
PubMed1982

The effects of lead and of cadmium on the mass photoreceptor potential: the dose-response relationship.

The effects of micromolar (1.0-60.0 microM) amounts of lead and of cadmium on the light response of photoreceptors were studied using the isolated, perfused bullfrog retina. The effect of lead in depressing rod activity is readily and fully reversible. Lead is very effective in depressing the rod response at concentrations as low as 1.0 microM, but the effect of lead saturates at about 25.0 microM with about 34% depression of the rod response. At the higher concentrations some spontaneous recovery of rod response amplitude is observed shortly after exposure of the retina to lead begins. The cone response is affected by lead only rarely and then only at the higher concentrations. When affected, the cone response is enhanced rather than depressed. The effects of cadmium are generally similar to those of lead. However, saturating concentrations of cadmium depress the rod response to a greater degree than lead and the cadmium effects are not as readily reversible as the effects of lead at the higher concentrations. Cones are much more sensitive to cadmium than they are to lead and 60.0 microM cadmium always enhances cone response amplitude. The results of experiments in which lead and cadmium were both added to the retinal perfusate indicate to us that cadmium and lead both affect the same sensitive site or sites responsible for generating the rod response, but that cadmium affects an additional site that is not sensitive to lead. The depressive effects of lead and of cadmium on the rod response are discussed in terms of the postulated mechanisms of transduction in the vertebrate photoreceptor.

Animals↗
PubMed1982

Rapid dark adaptation of bullfrog rods is delayed by barium.

With use of sodium aspartate, the late receptor potential of the excised, perfused bullfrog retina was isolated. By means of a two-flash technique, rapid dark adaptation of rods was monitored. As in cones, barium ions were found to delay the onset of rapid dark adaptation of rods, but the rate of recovery, once begun, was virtually unaffected. The effect of barium on the amplitude-intensity relationship of rods was also determined. Unlike its ability to dramatically increase the amplitude of the receptor potential of rods, barium had no effect on the absolute threshold of rods. We propose that barium ions act on the enzyme system postulated to govern the onset of rapid dark adaptation of rods and suggest that a reduction in the activity of an ATP protein kinase might be the basis for this effect.

Adenosine Triphosphate↗
PubMed1980

Development of neurotensin-immunoreactive nerve cells in organotypic cultures of embryonic rat spinal cord.

Neurotensin was localized by the indirect immunofluorescence method in developing organotypic cultures made from slices of the lumbar spinal cord of rat embryos (14-17 days gestation). Less than half of the cultures contained fluorescent cells, and in these specific immunofluorescence was confined to groups of neurones situated in the dorsolateral region of the explants. The neurones became morphologically fully developed after 21 days in culture. Their axons grew up to 1.7 mm in length and travelled within fibre bundles which were oriented around the circumference of the explant. The axonal growth patterns of spinal neurotensin-immunoreactive neurones in tissue culture suggest that they may project over relatively long distances in the rat spinal cord in situ.

Animals↗
PubMed1978

The effects of cytochalasin B and colchicine on cell motility and ultrastructure in primary cultures of malignant gliomas.

Primary tissue cultures of human gliomas were treated with cytochalasin B (0.5--60 microgram/ml for 90 min). Cell motility was inhibited irreversibly in glial tumour cells, but the effect was reversible on the mesenchymal cells growing in culture in the lower dose range. Cell adhesion was considerably reduced as the dose was increased, as was the capacity for cells to spread on a surface from suspension. Low concentrations of cytochalasin B caused negligible cell death and little disruption of cell ultrastructure. However, increases in dose were accompanied by a greater predominance of rough endoplasmic reticulum and inclusions and aggregation of microfilament bundles. As seen by scanning electron microscopy, cytochalasin B caused the withdrawal of peripheral cell borders, disappearance of ruffles and the breakdown of cytoplasmic lamellae. Charateristic surface blebs and folds appeared in their place. By comparison, colchicine (1--10 microgram/ml) caused a less marked and non-specific reversible reduction in cell motility on both glial and mesenchymal cells. No significant change in cell adhesion or spreading took place even at high doses, although at all concentrations gross disruption of the cell surface took place with changes in ultrastructure characterised by loss of cytoplasmic microtubules and aggregation of 10 nm filaments.

Brain Neoplasms↗
PubMed1978

Scanning electron microscopy of malignant gliomas. A comparative study of glioma cells in smear preparations and in tissue culture.

Smear preparations from 15 malignant gliomas, 2 metastatic carcinomas and from normal brain were examined by scanning electron microscopy. Tissue culture preparations from malignant gliomas were also studied. In the better differentiated areas of gliomas, the cells in smears were stellate with multiple long interweaving processes 0.25--1.3 micrometer in diameter which could be distinguished from myelinated nerve fibers (1.3--5 micrometer) and from fibrin (0.08--0.3 micrometer) by their thickness and arrangement in the tissue. The relationship of glial processes to blood vessels within the tumour was well demonstrated in smears. Metastatic carcinoma cells lacked the processes seen in glioma cell smears and did not show the same relationship to blood vessels. The more anaplastic glioma cells had fewer processes and ovoid cell bodies covered with surface ruffles and microvilli similar to the cell membrane projections in the nuclear regions of glioma cells in culture. The relationship of the surface morphology of glioma cells in smears to the known invasive nature of these tumours is discussed.

Brain Neoplasms↗
PubMed1978

Lucibufagins: Defensive steroids from the fireflies Photinus ignitus and P. marginellus (Coleoptera: Lampyridae).

Feeding tests with thrushes (Hylocichla spp.) led to the isolation of three novel steroid pyrones from fireflies (Photinus ignitus and P. marginellus) responsible, in part at least, for the unpalatability of these insects to the birds. The term lucibufagin is coined for these steroidal pyrones. The closest known relatives of lucibufagins are the familiar cardiotonic bufadienolides, found in certain toads and plants.

Journal Article↗
PubMed1978

Induction of some features of glial differentiation in primary cultures of human gliomas by treatment with dibutyrl cyclic AMP.

Explants from 18 gliomas were cultured for periods up to 7 weeks and studied by light microscopy scanning and transmission electron microscopy. Well-differentiated tumor tissue gave rise to early outgrowths of stellate cells showing process orientation. Poorly-differentiated tissue produced a more haphazard out-growth of pleomorphic cells with few processes and flattened pseudopodia. Mean circadian cell displacement was several times greater in poorly-differentiated cells, but was significantly and reversibly reduced by treatment and dibutyryl cAMP (5 X 10(-4)M) for 48 h. Reduction in motility was directly correlated with a change in cell morphology to a more stellate form. Well-differentiated cells had a smooth surface with ruffling restricted to the ends of processes and highly orientated glial filament and microfilament bundles. The poorly-differentiated cell surface had a microvillous, blebbed appearance and ruffling regularly occurred around the edge of the cytoplasm. Glial filaments and microfilaments were fewer and less well orientated in the poorly-differentiated cells; sites of adhesion to the substratum were fewer than in well-differentiated cells. Treatment of malignant cultures with dibutyryl cAMP resulted in smoothing of the cell surface, retraction of processes into thin pseudopodia and the appearance of microfilament bundles within the cells. These features marked the apparent cyto-differentiation. However, there was a loss of attachment, disappearance of microtubules and loss of glial filaments in the cytoplasm which was not compatible with differentiation. Intracellular recordings of membrane potentials gave a significantly higher mean value for well-differentiated cells. The mean membrane potential and input resistance of poorly-differentiated cells was unchanged by the addition of dibutyryl cAMP. The results of this study suggest that some, but not all, features of mature glia are restored in malignant tumour cells by cAMP treatment.

Brain Neoplasms↗
PubMedDate not supplied

Modulation of rod, but not cone, cGMP-gated photoreceptor channels by calcium-calmodulin.

Inside-out patches containing cGMP-gated channels were excised from catfish rod or cone outer segments and held under voltage clamp. The net cGMP-dependent currents elicited by saturating and subsaturating concentrations of cGMP at +/-30 mV were measured and the dependence of current upon cGMP concentration was determined. The apparent affinity of the channel for its ligand was estimated by fitting these data with the Hill equation. The concentration of cGMP required to give half the maximum current (K1/2) in rod and cone channels at +30 mV was approximately 28 microM and approximately 37 microM, respectively, and was weakly voltage dependent. Thus, cone channels have an intrinsically higher K1/2 than rod channels. For both types of channel, the Hill coefficient was approximately 2.3. In the presence of calcium-calmodulin, the apparent affinity of the rod channel for cGMP decreased by about twofold, but the apparent affinity of the cone channels was unaffected. These results indicate that the open probability of the cone channel for its ligand cannot be modulated by calmodulin. This represents the first significant departure between rod and cone photoreceptors in mechanisms used by phototransduction and suggests that the beta subunit of the cone channel must be different from that of the rod channel.

Animals↗
PubMedDate not supplied

Single cyclic GMP-activated channel activity in excised patches of rod outer segment membrane.

The plasma membrane of retinal rod outer segments contains a cyclic GMP-activated conductance which appears to be the light-sensitive conductance involved in phototransduction. Recently, it has been found that this conductance is partially blocked by Mg2+ and Ca2+ at physiological concentrations, thus possibly accounting for the absence of observable single-channel activity in excised membrane patches and for the unusually small apparent unit conductance deduced from noise measurements on intact cells. We now report that, as expected from this idea, single cGMP-activated channel activity can be detected from an excised rod membrane patch in the absence of divalent cations. The most prominent unitary current had a mean conductance of approximately 25 pS. Both individual channel openings (mean open time approximately 1 ms) and short bursts of openings (mean burst duration of about a few milliseconds) were observed. In addition, there were smaller events which probably represented other states of the conductance. The mean current increased with the third power of cGMP concentration, suggesting that there are at least three cGMP-binding sites on the channel molecule. With 0.2 mM Mg2+ in the cGMP-containing solution, a flickering block of the open channel was observed; the effect of Ca2+ was similar. The results resolve a puzzle about the light-sensitive conductance by demonstrating that it is an aqueous pore rather than a carrier.

Ambystoma↗
PubMedDate not supplied

Effect of neonatal capsaicin on peptide-containing primary afferent fibres, eosinophil distribution and hyperresponsiveness in rat lung tissue following experimentally induced eosinophilia.

Treatment of neonatal rats with capsaicin causes a 92.4% loss of calcitonin-gene-related-peptide-immunoreactive unmyelinated sensory afferent fibres in the airways epithelium, vascular smooth muscle and perivascular adventitial layer of lung tissue compared with vehicle-treated controls. Rats were administered Sephadex particles i.v. 8-10 weeks after either capsaicin or vehicle treatment at birth in order to induce a granulomatous tissue inflammation, peripheral blood eosinophilia and pulmonary eosinophil invasion [Laycock et al., Int Arch Allergy Appl Immunol 1986;81:363-367]. The animals also exhibited lung hyperreactivity in vitro in response to carbachol and serotonin (5HT). In Sephadex-treated rats, capsaicin pretreatment did not affect the number of inflammatory cells in peripheral blood, the number of eosinophils in lung tissue, or the distribution of eosinophils in the adventitial tissue of blood vessels. Potencies of concentration-related contractures of lung tissue to 5HT and carbachol were increased by 50- to 100-fold in Sephadex-treated animals compared to controls, but in neither group was potency influenced by capsaicin pretreatment at birth. Recruitment and subsequent regional distribution of inflammatory cells in lung tissue and the increase in lung hyperresponsiveness exhibited in this model of asthma do not appear to involve neuropeptides released from primary afferent neurones.

Afferent Pathways↗