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Biomedical subjects

C E Morris

Publications and source records attributed to C E Morris.

At least 55 records · Page 3Linked to original sources
PubMed1994

Effects of several environmental factors on sweetpotato growth.

Effects of relative humidity, light intensity and photoperiod on growth of 'Ga Jet' and 'TI-155' sweetpotato cultivars, using the nutrient film technique (NFT), have been reported. In this study, the effect of ambient temperature regimes (constant 28 degrees C and diurnal 28:22 degrees C day:night) and different CO2 levels (ambient, 400, 1000 and 10000 microliters/L--400, 1000 and 10000 ppm) on growth of one or both of these cultivars in NFT are reported. For a 24-h photoperiod, no storage roots were produced for either cultivar in NFT when sweetpotato plants were grown at a constant temperature of 28 degrees C. For the same photoperiod, when a 28:22 degrees C diurnal temperature variation was used, there were still no storage roots for 'TI-155' but the cv. 'Ga Jet' produced 537 g/plant of storage roots. For both a 12-h and 24-h photoperiod, 'Ga Jet' storage root fresh and dry weight tended to be higher with a 28:22 degrees C diurnal temperature variation than with a constant 28 degrees C temperature regime. Preliminary results with both 'Ga Jet' and 'TI 155' cultivars indicate a distinctive diurnal stomatal response for sweetpotato grown in NFT under an ambient CO2 level. The stomatal conductance values observed for 'Ga Jet' at elevated CO2 levels indicated that the difference between the light- and dark-period conductance rates persisted at 400, 1000, and 10000 microliters/L.

Biomass↗
PubMed1994

FMRFamide and membrane stretch as activators of the Aplysia S-channel.

The long-standing distinction between channels and transporters is becoming blurred, with one pump protein even able to convert reversibly to a channel in response to osmotic shock. In this light, it is plausible that stretch channels, membrane proteins whose physiological roles have been elusive, may be transporters exhibiting channel-like properties in response to mechanical stress. We recently described a case, however, where this seems an unlikely explanation. An Aplysia K channel whose physiological pedigree is well established (it is an excitability-modulating conductance mechanism) was found able to be activated by stretch. Here we establish more firmly the identity of this Aplysia conductance, the S-channel, as a stretch channel. We show that the permeation and fast kinetic properties of the stretch-activated channel and of the FMRFamide-activated S-channel are indistinguishable. We have also made progress in extending the kinetic analysis of the stretch channel to situations of multiple channel activity. This analysis implements a novel renewal theory approach and is therefore explained in some detail.

Animals↗
PubMed1994

Delayed activation of single mechanosensitive channels in Lymnaea neurons.

Some stretch-activated (SA) channels challenged with suction jumps exhibit adaptation, a dynamic behavior that can be overlooked because of its mechanical fragility. In previous studies of neuronal SA K channels, we detected no adaptation, but the protocols used were not designed to detect dynamics. Here, we reproduce the adaptation seen by others in Xenopus SA cationic (Cat) channels but show that, with the same protocol, no adaptation occurs with SA K channels. Instead, SA K channels exhibit a different dynamic behavior, delayed activation. Lymnaea SA K channels subjected to pressure jumps responded after a 1- to 4-s delay with a gradual, rather than abrupt, onset of activation. The delay was pressure dependent and was longer for patches from older cultured neurons. Delayed responses were fragile like SA Cat channel adaptation; they disappeared with repeated stimuli. Cytochalasin D decreased the delay and increased the stretch activation of SA K channels. Unlike SA Cat channel adaptation, which occurs only at hyperpolarized potentials, SA K channel delay was not voltage dependent. We note that once SA Cat and SA K channels are "stripped" of their fragile (cytoskeleton-dependent?) dynamics, however, their gating behaviors show little fundamental difference; both are stretch activatable and have a higher open probability at depolarized potentials.

Adaptation, Physiological↗
PubMed1994

Enamel opacities and dental caries in children who used a low fluoride toothpaste between 2 and 5 years of age.

A recent clinical trial investigated the cariostatic effectiveness of a low (550 ppm) fluoride toothpaste in comparison with a standard (1050 ppm) control paste in pre-school children who were 2-years-old at the start of the 3-year trial. The present study has investigated the prevalence of enamel opacities in permanent incisor teeth and of caries in children who had taken part. As well as children from test and control groups, a third group of non-trial children were included in the sample. A total of 1,523 children were examined in schools and had photographs taken of their upper permanent incisor teeth. The latter were scored using the Thylstrup and Fejerskov (TF) index for fluorosis and the modified Developmental Defects of Enamel (DDE) index. Differences between the groups were small in real terms but using the TF index the child and tooth prevalence of opacities were significantly lower in the children who had used the test paste with a lower fluoride content; the same trend was seen in diffuse defects scored using the modified DDE index. There was no significant difference in the prevalence of caries in either primary or permanent teeth although the trend in both cases was for slightly more disease in children who had used the test paste.

Cariostatic Agents↗
PubMed1992

Are stretch-sensitive channels in molluscan cells and elsewhere physiological mechanotransducers?

Single-channel recordings of dozens of cell types, including invertebrate (molluscan) and vertebrate heart cells, reveal stretch-sensitive ion channels. The physiological roles of these channels are undoubtedly diverse but it is usually assumed that the roles they play are related to the channels' mechanosensitive gating. Whether this assumption is valid remains to be seen. Attempts to connect the single-channel observations with the mechanical aspects of physiological or developmental processes are discussed. In the case of molluscan cells, recent work suggests that their stretch channels have physiological functions unrelated to mechanosensitive gating.

Animals↗
PubMed1992

Stretch activation of the Aplysia S-channel.

The S-channel, a receptor-mediated K+ channel of Aplysia sensory neurons which functions in neuromodulation, bears a strong resemblance to the ubiquitous stretch-activated channels of snail neurons. Snail neuron stretch channels are stretch sensitive only in the patch, not at the macroscopic level, a situation which leaves open the question of their physiological role. If S-channels resemble snail stretch channels because both belong to the same general class of channels, the S-channel, too, should display stretch sensitivity in the patch. We show, using single-channel recording, that the S-channel can be activated by stretch. Furthermore, we show that Aplysia neurons in general have stretch-activated K+ channels. We suggest that the stretch-sensitive K+ channels of molluscan neurons and other preparations (e.g., Drosophila muscle, snail heart) are S-like channels, i.e., receptor-mediated channels which adventitiously exhibit mechanosensitivity in the patch.

Abdomen↗
PubMed1992

Growing root, tuber and nut crops hydroponically for CELSS.

Among the crops selected by the National Aeronautics and Space Administration for growth in controlled ecological life support systems are four that have subsurface edible parts -- potatoes, sweet potatoes, sugar beets and peanuts. These crops have been produced in open and closed (recirculating), solid media and liquid, hydroponic systems. Fluorescent , fluorescent plus incandescent and high pressure sodium plus metal halide lamps have proven to be effective light sources. Continuous light with 16 degrees C and 28/22 degrees C (day/night) temperatures have produced highest yields for potato and sweet potato, respectively. Dry weight yields of up to 4685, 2541, 1151 and 207 g m-2 for for potatoes, sweet potatoes, sugar beets and peanuts, respectively, have been produced in controlled environment hydroponic systems.

Arachis↗
PubMed1992

Channels activated by stretch in neurons of a helix snail.

Single-channel recordings from central neurons of the helix snail, Cepaea nemoralis, revealed two types of channels that could be activated by stretch (i.e., by the membrane deformation produced when suction is applied to the patch pipette). One, a K+ channel (58 pS in physiological solution), was evident in excised and cell-attached patches. Its conductance in symmetrical [K+] solutions indicated a channel of high K+ permeability (PK = 3.4 x 10(-13) cm/s). Though osmoregulation has been suggested as a function for such channels, comparisons among molluscs indicate osmotic milieu does not govern their expression; Cepaea is terrestrial, and stretch-activated K+ channels similar to those described here occur in aquatic and marine molluscs. The second type of channel, observed only in excised patches, was Cl- permeant; it had a large conductance (130 pS) and was inactive prior to patch excision. Membrane tension may not be the physiological activator of either the K+ or Cl- channel; the channels are designated as stretch-activated channels on the basis of their experimental behaviour during single-channel recording.

Animals↗
PubMed1991

Failure to elicit neuronal macroscopic mechanosensitive currents anticipated by single-channel studies.

Mechanosensitive channels can be observed in most cell types during single-channel recording and have been implicated in many cellular processes. Potassium-selective single-channel currents, both stretch-activated and stretch-inactivated, can be observed in growth cones and cell bodies of Lymnaea stagnalis neurons. Equivalent macroscopic mechanosensitive currents could not, however, be elicited while applying various mechanical stimuli. This discrepancy suggests that single-channel mechanosensitivity is an artifact of patch recording.

Animals↗
PubMed1989

Stretch-inactivated ion channels coexist with stretch-activated ion channels.

Stretch-activated ion channels of animal, plant, bacterial, and fungal cells are implicated in mechanotransduction and osmoregulation. A new class of channel has now been described that is stretch-inactivated. These channels occur in neurons, where they coexist with stretch-activated channels. Both channels are potassium selective. The differing stretch sensitivities of the two channels minimize potassium conductance over an intermediate range of tension, with the consequence that, over this same range, voltage-gated calcium channels are most readily opened. Thus, by setting the relation between membrane tension and transmembrane calcium fluxes, stretch-sensitive potassium channels may participate in the control of calcium-dependent motility in differentiating, regenerating, or migrating neurons.

Animals↗
PubMed1989

Utilization of sweet potatoes in controlled ecological life support systems (CELSS).

A number of studies have selected the sweet potato as a potentially important crop for CELSS. Most hydroponic studies of sweet potatoes have been short term (<80 days). Full term (90 to 150 days) studies of sweet potatoes in hydroponic systems were needed to understand the physiology of storage root enlargement and to evaluate sweet potato production potential for CELSS. Early and late maturing sweet potato varieties were crown in hydroponic systems of different types--static with periodic replacement, flowing with and without recirculation, aggregate, and non-aggregate. In a flowing system with recirculation designed at Tuskegee University using the nutrient film technique (NFT), storage root yields as high as 1790 g were produced with an edible growth rate of up to 66 g m-2 d-1 and a harvest index as high as 89% under greenhouse conditions. Preliminary experiments indicated high yields can be obtained in controlled environmental chambers. Significant cultivar differences were found in all systems studied. Nutritive composition of storage roots and foliage were similar to field-grown plants. The results indicate great potential for sweet potato in CELSS.

Biomass↗
PubMed1989

Activation by curare of acetylcholine receptor channels in a murine skeletal muscle cell line.

Curare action on nicotinic acetylcholine receptors has a number of facets, of which the best known is competitive antagonism. Here we describe the weak agonist action of 10(-5) M curare on the murine skeletal muscle cell line, G8. Although curare induces no depolarization in G8 cells, single-channel recordings reveal short-lived curare-induced currents. A feature of these brief events is the multiplicity of conductance levels (of the four levels with conductances of 48, 37, 14, and 6 pS, none had a lifetime greater than 1.5 ms). Most well-resolved events (about 17% of which are to a subconductance) last less than 0.5 ms, with activation occurring predominantly as isolated events rather than in bursts. Agonism is not, however, a high probability action for curare: calculations based on the frequency of events at half-saturating conditions suggest that curare-induced channel openings occur during less than 1% of acetylcholine receptor-curare binding episodes. The outcome is (a) an agonist action too feeble to perturb the membrane voltage and (b) a powerful competitive antagonist action.

Animals↗
PubMed1989

Stretch-activated ion channels in growth cones of snail neurons.

Using single-channel recording, we show that neurons contain ion channels sensitive to membrane tension. Neurons isolated from the snail, Lymnaea stagnalis, actively rearborized in culture yielding cell bodies and growth cones suitable for patch clamping. All neurons contained, in both their soma and growth cones (at a density of approximately 1-2 micron-2), stretch-activated channels highly selective for K+. The presence of this mechanosensitive channel in the motile region of the neuron, a region characterized by insertion of new membrane--the growth cone--is of particular interest. Under physiological conditions, the channel was permeable to K+, but not to Na+ or Cl-. Its conductance to K+ under these conditions was approximately 44 pS. Channel activation was steeply dependent on membrane tension, showing thresholds at between -50 to -100 mm Hg (suction was applied through the recording pipette). Kinetic analysis indicated that the stretch-dependent increase in the channel's open probability was related to a long closed state rather than to one of the open states. Given the importance of Ca2+ in the regulation of growth cone motility, we speculate that this stretch-activated K+ channel could play a role in neurite elongation by a tension-dependent modulation of membrane voltage which in turn would act on voltage-gated Ca2+ channels.

Animals↗
PubMed1986

Cloning and expression of the bacteriophage T3 RNA polymerase gene.

The gene that encodes the RNA polymerase of bacteriophage T3 (gene 1) has been cloned into a pBR322 derivative under the control of an inducible lacUV5 promoter. Large quantities of the protein are synthesized after induction of cells that carry this plasmid. RNA polymerase purified from these overproducing cells selectively initiates transcription from T3 promoter sequences as demonstrated by transcription of a dual promoter plasmid that carries both T3 and T7 promoters. Cells that carry the T3 RNA polymerase gene can complement amber mutants of T3 that are defective in gene 1 but not gene 1 amber mutants of T7, and vice versa; this experiment demonstrates the specificity of these enzymes in vivo.

Base Sequence↗