Calcium efflux from amphibian sciatic nerve

1983 ◽  
Vol 61 (9) ◽  
pp. 1085-1089 ◽  
Author(s):  
R. E. Snyder ◽  
D. W. O'Brien
Keyword(s):  
Sciatic Nerve ◽  
Xenopus Laevis ◽  
Diffusion Barrier ◽  
Half Life ◽  
Extracellular Space ◽  
Calcium Efflux ◽  
Coefficient Of Diffusion ◽  
Perineurial Sheath

Eight Xenopus laevis were injected intraperitoneally with 45CaCl2 and 16–18 h later an unbranehed section from each sciatic nerve was removed. Efflux measurements of nerve from which the perineurial sheath had been removed could be described by three compartments of approximately eqvial size with half-lifes of 2.37 ± 0.76 (SD), 30.3 ± 17.3, and 196 ± 61 min, the shortest lived compartment representing diffusion from the extracellular space with a coefficient of diffusion of 2.1 ± 0.7 × 10−6 cm2/s. Efflux from nerve in which the perineurium remained intact was characterized by a half-life of 862 ± 399 min resulting from the sheath acting as a diffusion barrier of permeability 3.4 ± 1.6 × 10−7 cm/s. The perineurium was found to bind or sequester a quantity of calcium 1–2 times that contained in an equal volume of plasma.

Calcium content of frog sciatic nerve during chronic hypocalcemia and hypercalcemia

1987 ◽  
Vol 253 (4) ◽  
pp. R655-R660
Author(s):  
K. C. Wadhwani ◽  
H. Levitan ◽  
S. I. Rapoport
Keyword(s):  
Plasma Concentration ◽  
Sciatic Nerve ◽  
Peripheral Nerve ◽  
Plasma Concentrations ◽  
Calcium Regulation ◽  
Calcium Content ◽  
Plasma Calcium ◽  
Ionized Calcium ◽  
Steady State Plasma Concentration ◽  
Perineurial Sheath

We examined the calcium contents of desheathed peripheral nerve, perineurial sheath, and whole sciatic nerve in the frog as a function of the steady-state plasma concentration of ionized calcium. Chronic hypocalcemia was induced by parathyroidectomy and by bathing frogs in a phosphate medium. Chronic hypercalcemia was induced by administering vitamin D3 and by bathing frogs for up to 2 wk in medium containing 50 mM CaCl2. Calcium was measured with a calcium-sensitive electrode and by atomic absorption spectroscopy. The calcium contents (mmol/kg wet wt) in whole nerve, desheathed nerve, and the perineurial sheath varied linearly with slopes of 0.72, 0.71, and 1.72, respectively, with plasma concentration (mM) of ionized calcium, which ranged from 0.3 to 8.0 mM. In the same animals the calcium content in the cerebrum was independent of plasma calcium between 0.5 and 1.5 mM but rose at higher plasma concentrations. Our results indicate that net calcium concentration in the frog peripheral nerve is not regulated during chronic hypocalcemia and hypercalcemia, whereas brain calcium is regulated at plasma calcium concentrations less than 1.5 mM. The lack of calcium regulation in the nerve is attributed to the lack of calcium regulation in the endoneurial compartment.

scholarly journals Brain extracellular space as a diffusion barrier

2011 ◽  
Vol 14 (7) ◽  
pp. 309-325 ◽  
Author(s):  
Charles Nicholson ◽  
Padideh Kamali-Zare ◽  
Lian Tao
Keyword(s):  
Diffusion Barrier ◽  
Extracellular Space ◽  
Brain Extracellular Space

The Decay of Xenopus laevis Mitochondrial rRNA in the Presence of Ethidium Bromide or Actinomycin D

1974 ◽  
Vol 52 (10) ◽  
pp. 911-915
Author(s):  
P. G. Young ◽  
A. M. Zimmerman
Keyword(s):  
Xenopus Laevis ◽  
Ethidium Bromide ◽  
Half Life ◽  
Actinomycin D ◽  
Initial Increase ◽  
Mitochondrial Rna ◽  
Chase Period ◽  
Mitochondrial Rrna ◽  
Cytoplasmic Rna ◽  
Xenopus Laevis Embryos

The effect of ethidium bromide and actinomycin D on prelabelled mitochondrial RNA was studied in Xenopus laevis embryos. Mitochondrial rRNA was found to decay with a half-life of 2–2.5 h following an initial lag of < 2 h. There was an initial increase in incorporation into mitochondrial rRNA in the presence of actinomycin D but not in the presence of ethidium bromide. Radioactivity in mitochondrial 4 S RNA rises and then is relatively stable for the duration of the chase period. Cytoplasmic rRNA and 4 S RNA are stable under the chase conditions used, and, in the presence of ethidium bromide, cytoplasmic RNA continues to be synthesized.

Stability of RNA in developing Xenopus embryos and identification of a destabilizing sequence in TFIIIA messenger RNA

Development ◽  
1988 ◽  
Vol 102 (4) ◽  
pp. 837-852 ◽  
Author(s):  
R. Harland ◽  
L. Misher
Keyword(s):  
Xenopus Laevis ◽  
Half Life ◽  
Messenger Rna ◽  
Untranslated Region ◽  
Circular Rna ◽  
Midblastula Transition ◽  
Rna Transcripts ◽  
Xenopus Embryos ◽  
A Site

Synthetic capped RNA transcripts injected into fertilized eggs of Xenopus laevis have a half-life of 3–4 h. Addition of a long (approximately 200 nucleotide) poly(A) tail increases the half-life to 6–8 h which approaches the half-life of natural polyadenylated globin RNA injected into embryos. Since exonucleolytic action alone could account for the degradation of RNA, we tested whether circular RNA is stable after injection and find that circles are exceptionally stable (half-life greater than 40 h). After the midblastula transition, polyadenylated chloramphenicol transferase (CAT) mRNAs transcribed from injected plasmids have a half-life of 2.5 h. Insertion of a 1000 nucleotide 3′ untranslated region from the Xhox-36 gene into the transcripts does not affect the half-life. In contrast to the finding that internal sequences do not affect stability, we find that sequences from the TFIIIA message reduce the half-life of CAT mRNA from 2.5 h to less than 30 min. We conclude that most RNAs are degraded exonucleolytically from the 3′ end, but specialized internal sequences can greatly destabilize the RNA, possibly by acting as a site for an endonuclease.

Studies on amphibian yolk. VII. Serum phosphoprotein synthesis by vitellogenic females and estrogen-treated males of Xenopus laevis

1968 ◽  
Vol 46 (8) ◽  
pp. 953-959 ◽  
Author(s):  
R. A. Wallace ◽  
D. W. Jared
Keyword(s):  
Single Dose ◽  
Xenopus Laevis ◽  
Chorionic Gonadotropin ◽  
Human Chorionic Gonadotropin ◽  
Half Life ◽  
Yolk Proteins ◽  
Estradiol 17Β

Female toads given 1000 units of human chorionic gonadotropin ovulated within 24 h and began to synthesize a phosphoprotein which appeared, but did not accumulate, in the serum (physiological half-life, 2 days). The period of synthesis lasted about 30 days, after which mature oocytes were once again observed in the ovary. Male toads given a single dose of 0.1–1.0 mg estradiol-17β also immediately began to synthesize a phosphoprotein. The rate of maximum synthesis and the length of time for the maximum to be reached were directly proportional to the amount of estrogen administered. The serum phosphoprotein in male toads, however, had a physiological half-life of approximately 40 days. Ovariectomized females produced a serum phosphoprotein with a physiological half-life similar to that of males. We therefore concluded that under normal conditions the circulating phosphoprotein produced by the liver of the female as a response to estrogen is accumulated by the vitellogenic ovary. The serum phosphoprotein is apparently a lipophosphoprotein complex from which at least one of the yolk proteins, phosvitin, may be derived.

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