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Biomedical subjects

R Christen

Publications and source records attributed to R Christen.

87 records · Page 5Linked to original sources
PubMed1983

Interactions between sperm and sea urchin egg jelly.

The addition of egg jelly to sea urchin sperm induces multiple changes in morphology and behavior. When jelly is added to sperm diluted in seawater, the acrosome reaction is triggered, the mitochondrion rounds up, the internal pH is transiently alkalinized and then reacidified, and respiration becomes uncoupled and rapidly decreases. Sperm also become unable to fertilize eggs within a few minutes after jelly addition. In order to explore in more detail the effect of egg jelly on sperm, we have studied the response to jelly in the presence of inhibitors of the acrosome reaction. When jelly is added to sperm under conditions which are inhibitory for the acrosome reaction, an alkalinization takes place without the subsequent reacidification, the mitochondria remain coupled, and respiration and intracellular ATP levels remain high. Sperm viability is prolonged by some of these conditions, but not others. The addition of jelly to sperm in the absence of calcium elicits an internal alkalinization but no other rapid change in sperm physiology. The capacity of egg jelly to alter sperm physiology even when the overall acrosome reaction is inhibited indicates that some of the physiological changes either are early events in the triggering pathway that happen before the inhibitory step or are unrelated to the acrosomal reaction itself. The reacidification of the internal pH, the uncoupling and decrease of the respiration, and the decrease of the ATP levels might be linked together by the large influx of calcium that occurs after the acrosome reaction.

Acrosome↗
PubMed1983

Acidic vesicles and the uptake of amines by sea urchin eggs.

The radioactive amine [14C]methylamine is accumulated to a great extent by eggs, with kinetics that are dependent upon temperature (Q10 = 5) and sensitive to metabolic inhibitors. Efflux of [14C]methylamine from eggs (preloaded with tracer concentrations) is increased immediately after fertilization or NH4Cl activation. Fluorescent amines (9-aminoacridine (9AA) and acridine orange (AO)) are concentrated in small intracellular compartments, presumably vesicles. The possible role of these vesicles in the accumulation of amines by sea urchin eggs and the activation of the metabolism that ensues is discussed.

Acridine Orange↗
PubMed1983

31P-NMR analysis of sea urchin sperm activation. Reversible formation of high energy phosphate compounds by changes in intracellular pH.

31P-NMR has been used to estimate the internal pH (pHi) of sperm from the sea urchin Strongylocentrotus purpuratus. The values for pHi obtained from the chemical shift of inorganic phosphate agree well with those obtained from amine accumulation. At low pHi, when sperm are quiescent (immotile and non-respiring), they accumulate phosphocreatine (PCr), but have a low level of inorganic phosphate (Pi). Conversely, when the pHi is elevated, sperm respiration and motility are activated, PCr is decreased and Pi is increased. This change is reversible upon decrease of the pHi, whereupon respiration and motility are arrested, Pi disappears and PCr increases. We conclude that the overall balance of energy metabolism, and thus the phosphate potential, of sea urchin sperm are under the control of the pHi.

Adenosine Triphosphate↗
PubMed1982

Elevation of the intracellular pH activates respiration and motility of sperm of the sea urchin, Strongylocentrotus purpuratus.

The internal pH (pHi) of sperm of the sea urchin, Strongylocentrotus purpuratus, was estimated by measuring the accumulation of the weak bases [14C]methylamine, [14C]diethylamine, or 9-aminoacridine under conditions where cellular respiration was activated or inhibited. When 9-aminoacridine fluorescence measurements are corrected for binding to intracellular components, the pHi estimates agree quantitatively with those obtained from [14C]amine distributions. The pHi of sperm decreased when the intracellular [K+] was elevated above the physiological value of 10 mM, or when the external pH was substantially decreased below the physiological 8.0, or when Na+ was absent from the seawater. At the decreased pHi values, sperm respiration and motility were inhibited; conversely, both respiration and motility increased when the pHi was elevated. Increased respiration occurred whether the pHi was increased by altering the external pH, [K+] or [Na+], or by the addition of NH4Cl to the medium. In all cases, the activation of respiration and motility were linked, suggesting a unitary control mechanism, some possibilities for which are presented.

Animals↗
PubMed1981

Membrane potential depolarization and increased intracellular pH accompany the acrosome reaction of sea urchin sperm.

The intracellular pH and membrane potential in sperm of the sea urchin Strongylocentrotus purpuratus were investigated by using fluorescent and radiolabeled probes. The weak bases [14C]methylamine, [14C]diethylamine, and 9-aminoacridine were concentrated within sperm 5-fold or greater. The weak acid [14C]dimethyloxazolidine-2,4-dione (DMO) was excluded from sperm. These data suggested that the apparent intracellular pH is acidic with respect to seawater (pH 8.0). Induction of the acrosome reaction caused efflux of the amines and uptake of DMO, consistent with an increase in apparent intracellular pH of 0.1-0.2 pH unit. The presence of an internally negative membrane potential was indicated by estimating the distribution of [3H]tetraphenylphosphonium (Ph4P+) and [14C]SCN-. From SCN- exclusion we estimated a value of about -30 mV for the nonmitochondrial membrane potential, whereas from Ph4P+ accumulation an apparent potential of -90 to -150 mV was demonstrated. The membrane potentials obtained with Ph4P+ and SCN- were dependent upon the external K+ concentration, with increasing K+ leading to depolarization. Induction of the acrosome reaction led to efflux of Ph4P+ and uptake of SCN- for an approximate depolarization of about 30 mV, primarily due to the collapse of the plasma membrane potential.

Acrosome↗
PubMed1980

Changes in permeability of sea urchin egg membrane to urea after fertilization or activation.

1. Fertilization or artificial activation of the sea urchin egg, are known to increase the plasma membrane permeability to ions and small metabolites. We have examined the permeability properties of the egg membrane to urea. 2. Urea influx is not saturable and is slightly dependent on temperature. It is inhibited by phloretin. 3. Fertilization leads to a biphasic increase in urea flux kinetics. The first acceleration lasts about 10 min. The second acceleration is maintained at least up to the first cleavage. 4. The ionophore A 23187 mimics exactly fertilization. 5. Weak bases such as procaine lead to a gradual acceleration in urea flux kinetics. The response depends on the dose of procaine added. 6. The inhibitor of oxydative phosphorylation 2,4-DNP fails to block the accelerations triggered by fertilization or activation by A 23187. 7. We discuss the results in light of the early and late events of egg activation.

Animals↗
PubMed1980

Preferred listening levels for bands of speech in relation to hearing aid selection.

The Most Comfortable Loudness Level (MCL) was measured for 24 normal-hearing subjects, using narrow bands of speech having centre frequencies of 0.25, 0.5, 1.2 and 4kHz. MCL's were equivalent for octave band and one-third octave band stimuli. The sensation levels (SL) for various frequencies closely matched the SL of the 60 phon equal loudness contour for pure tones. It was concluded, for levels around MCL, sounds which are equally comfortable are equally loud and that equal loudness contours for pure tones are also applicable to narrow bands of speech. Some implications for hearing aid selection are discussed. However, this investigation was primarily a preliminary to other studies more directly related to hearing aid selection issues.

Adolescent↗
PubMed1979

Chloride permeability of sea urchin eggs.

We have examined the content and permeability of chloride in sea urchin eggs. After fertilization there is a large increase in the permeability to chloride. We discuss the mechanism underlying this permeability change and the generalized increase in ion permeability observed after fertilization.

Animals↗
PubMedDate not supplied

Phylogenetic relationships of human-pathogenic Cladosporium (Xylohypha) species inferred from partial LS rRNA sequences.

The controversy about the appropriate taxonomic placement of agents of subcutaneous and systemic mycoses in either Cladosporium or Xylohypha, both genera characterized by conidia being produced in dry, acropetal chains, was addressed with partial sequencing of LS ribosomal RNA. Observation of catenate anamorphs in species of Capronia (Ascomycotina, Herpotrichiellaceae), a genus which also has anamorphs in Exophiala, suggested the possibility of a close interrelationship of all human-associated taxa. To test this hypothesis, partial sequences of 43 strains of Cladosporium/Xylohypha were analysed. Human-pathogenic and saprophytic Cladosporium species were found to be phylogenetically distinct from each other and, on the basis of known teleomorph relationships, were considered to be anamorphs of Herpotrichiellaceae and Mycosphaerellaceae, respectively. They should therefore be classified in different anamorph-genera; Cladosporium being restricted to plant-associated species. A relatively large proportion of the Herpotrichiellaceae is presumed to be animal-associated. The black yeast genus Exophiala was also confirmed to be of herpotrichiellaceous relationship. The genus Xylohypha is unrelated.

Base Sequence↗
PubMedDate not supplied

Characterization of unusual alkaliphilic gram-positive bacteria isolated from degraded brown alga thalluses.

Two orange-pigmented Gram-positive, aerobic bacteria were isolated from enrichment culture during degradation of brown alga Fucus evanescens thalluses. In this work, atomic force microscopy (AFM) has been used to study the cell morphology. The non-contact mode imaging revealed unusual irregular coccoid shape of cells, possessing a single flagellum. Bacteria produced carotenoid pigments, were chemo-organotrophic, alkaliphilic and halo-tolerant growing well on nutrient media containing up to 15% NaCl. Growth temperature ranged from 5 to 45 degrees C. The DNA base compositions were 48 mol% G + C and the level of DNA similarity of two strains was conspecific (98%). A comparative phylogenetic analysis of 16S rRNA gene sequences revealed that the strain KMM 3738 tightly clustered with recently described Planococcus maritimus (99.9% 16S rRNA gene sequence similarity). DNA-DNA hybridisation experiments revealed that DNA from the KMM 3738 showed 12-15% and 16-35% of genetic relatedness with the DNA of type strains of the genera Planomicrobium and Planococcus, respectively, and 87% with DNA from Planococcus maritimus, indicating that new isolates belong to the later species.

Bacterial Typing Techniques↗