Blood–Brain Barrier Permeability to Sodium. Modification by Glucose or Insulin?

In order to explore the pathogenetic mechanism underlying the changes in blood-brain barrier sodium transport in experimental diabetes, the effects of hyperglycemia and of hypoinsulinemia were studied in nondiabetic rats. In untreated diabetes, the neocortical blood-brain barrier permeability for sodium decreased by 20% (5.6 +/- 0.7 versus 7.0 +/- 0.8 X 10(5) ml/g/s) as compared to controls. Intravenous infusion of 50% glucose for 2 h was associated with a decrease in the blood-brain barrier permeability to sodium (5.4 +/- 1.2 X 10(5) ml/g/s), whereas rats treated with an inhibitor of insulin-secretion (SMS 201-995, a somatostatin-analogue) had normal sodium permeability (7.3 +/- 2.0 X 10(5) ml/g/s). Acute insulin treatment of diabetic rats normalized the sodium permeability within a few hours as compared to a separate control group (7.7 +/- 1.1 versus 6.9 +/- 1.4 X 10(5) ml/g/s). To elucidate whether the abnormal blood-brain barrier passage is caused by a metabolic effect of glucose or by the concomitant hyperosmolality, rats were made hyperosmolar by intravenous injection of 50% mannitol. Although not statistically significant, blood-brain barrier sodium permeability increased in hyperosmolar rats as compared to the control rats (8.3 +/- 1.0 and 7.0 +/- 1.9 X 10(5) ml/g/s, respectively). It is concluded that either hyperglycemia per se or a glucose metabolite is responsible for the blood-brain barrier abnormality which occurs in diabetes. Further, we suggest that the specific decrease of sodium permeability could be the result of glucose-mediated inhibition of the Na+K+-ATPase localized at the blood-brain barrier.     

Cellular Stress Causes Accumulation of the Glucose Transporter at the Surface of Cells Independently of their Insulin Sensitivity

The stimulation of glucose transport in response to various types of stress has been studied. There is no relationship between effects of stress-inducing agents on glucose transport and their effects on cellular protein synthesis. Although the effect of stress on glucose transport appears analogous to its stimulation by insulin, cells that are slightly insulin-sensitive in terms of glucose transport (BHK cells) show a similar degree of stimulation as highly insulin-sensitive cells (differentiated 3T3-L1 cells). External labeling of the transporter protein with a photoactivatable derivative of mannose, 2-N-4-(1-azi-2,2,2-trifluoroethyl) benzoyl-1, 3-bis-(D-mannos-4-yloxy)-propylamine, shows that most of the increased glucose transport activity correlates with an increase in the amount of the transporter on the cell surface. Cells subjected to K⁺-depletion, which inhibits endocytosis and results in an accumulation of receptors at the cell surface, show the same increase in glucose transport as cells exposed to stress; stressed cells show no further increase in glucose transport when subjected to K⁺ depletion. These results support the view (Widnell, C.C., Baldwin, S.A., Davies, A., Martin, S., Pasternak, C.A. 1990. FASEB J 4:1634–1637) that cellular stress increases glucose transport by promoting the accumulation of glucose transporter molecules at the cell surface. Received: 20 June 1995/Revised: 29 September 1995     

Protein Tyrosine Kinase-Mediated Potentiation of Currents from Cloned NMDA Receptors

Abstract: Although serine/threonine phosphorylation has been more commonly recognized as a mechanism to modulate the function of ion channels and receptors, tyrosine phosphorylation is under increasing scrutiny. An important subtype of glutamate receptor, the NMDA receptor, is shown to be regulated by insulin via protein tyrosine kinase (PTK). NMDA currents through cloned receptors are potentiated by insulin in a subunit-specific manner. The insulin-mediated potentiation of NMDA current is diminished by inhibitors of PTKs. At least one exogenous cytosolic PTK, pp60^{c- src} , is also able to potentiate NMDA current. Because later application of PTK inhibitors can reverse the seemingly stable insulin-mediated potentiation of NMDA current, it appears that tyrosine residues responsible for potentiation are continually rephosphorylated by some long-term PTK activity that was induced via insulin treatment.     

Ultraviolet-sensitive ooplasmic factors are responsible for the development of an endoderm-specific alkaline phosphatase in the ascidian embryo

The ascidian egg contains muscle and endoderm determinants that play critical roles in the specification of muscle and endoderm cells, respectively. Endoderm cells of the ascidian embryo express alkaline phosphatase (AP) as a tissue-specific enzyme. We obtained egg fragments from the unfertilized eggs of Ciona savignyi by means of centrifugal force. The largest fragment (red fragments) contained the egg nucleus while other small fragments (black, clear and brown fragments) were anucleate. When inseminated, only red fragments developed into partial embryos, which showed only epidermis cell differentiation and, very rarely, AP activity. When red fragments were fused with other fragments, only black fragments promoted AP expression, suggesting that endoderm determinants were concentrated in the black fragments. A lower dose (1500 J/m²) of ultraviolet (UV) light did not eliminate the AP-promoting ability of black fragments, while this dose significantly repressed the ability to promote the expression of the muscle-marker. A higher dose (4500 J/m²) of UV light markedly reduced the AP-promoting activity of black fragments. These results suggest that factors for endodermal AP development are inactivated by UV irradiation, but are more resistant than muscle determinants.     

Spectral sensitivity of photoreceptors mediating phase-shifts of circadian rhythms in retinally degenerate CBA/J (rd/rd) and normal CBA/N (+/+) mice

Light-dark cycles are the most important time cue for the circadian system to entrain the endogenous circadian clock to the environmental 24 h cycle. Although photic entrainment of circadian rhythms is mediated by the eye in mammals, photoreceptors implicated in circadian photoreception remain unknown. In our previous study, retinally degenerate CBA/J (rd/rd) mice were found to have lower circadian photo-sensitivity for phase-shifting the locomotor activity rhythms than normal CBA/N(+/+) mice. In the present study, the spectral sensitivity for phase-shifting the rhythms was examined in order to characterize the photopigments involved in circadian photoreception of these mice. The spectral sensitivity of CBA/J-rd/rd mice clearly fitted to the Dartnall nomogram for a retinal₁-based pigment with a maximum at 480 nm, while the best fitted nomogram had a maximum at 500 nm in CBA/N- +/+ mice. These results suggest that circadian photopigments involved in CBA/J-rd/rd and CBA/N- +/+ mice may be different.     

Homogenisation and oxygen transfer rates in large agitated and sparged animal cell bioreactors: Some implications for growth and production

Because of concern for cell damage, very low agitation energy inputs have been used in industrial animal cell bioreactors, typical values being two orders of magnitude less than those found in bacterial fermentations. Aeration rates are also very small. As a result, such bioreactors might be both poorly mixed and also unable to provide the higher oxygen up-take rates demanded by more intensive operation. This paper reports experimental studies both of K _L a and of mixing (via pH measurements) in bioreactors up to 8 m³ at Wellcome and of scaled down models of such reactors at Birmingham. Alongside these physical measurements, sensitivity of certain cell lines to continuously controlled dO₂ has been studied and the oxygen up-take rates measured in representative growth conditions. An analysis of characteristic times and mixing theory, together with other recent work showing that more vigorous agitation and aeration can be used especially in the presence of Pluronic F-68, indicates ways of improving their performance. pH gradients offer a special challenge.     

荔枝和龙眼种子发育过程中ABA含量及对外源ABA敏感性的变化

在荔枝和龙眼种子发育过程中,内源ＡＢＡ水平先是上升,至大约７８～８０ＤＰＡ时出现高峰,之后两者ＡＢＡ含量均不断下降。果实成熟时采收的种子,ＡＢＡ含量比高峰时分别下降近６倍。另外,随着种子的发育,种子及其胚轴对外源ＡＢＡ的敏感性（ＳＡＢＡ）亦持续下降。１０－４ｍｏｌ／ＬＡＢＡ可以完全抑制９０ＤＰＡ前的荔枝和龙眼种子的萌发,但对成熟种子１０－２ｍｏｌ／ＬＡＢＡ亦不能抑制其萌发。龙眼种子离体胚轴的ＳＡＢＡ高于荔枝。ＡＢＡ含量与敏感性的这种变化可能是两种顽拗性种子成熟时萌动,进而不耐脱水贮藏的重要原因之一。     

Comparative studies on the dynamics of crosslinked insulin

Molecular dynamics simulations were carried out on an insulin crosslinked between the N-terminal A chain and the C-terminal B chain to form a so-called mini-proinsulin: N -^A1-N -^B29-diaminosuberoyl insulin (DASI). To investigate the influence of crosslinking on the dynamics of the insulin moiety, the bridge was removed from a transient DASI structure and simulation was carried on independently with the then unlinked (ULKI) as well as with the crosslinked species. The effects of crystal packing and quaternary interactions were checked by simulating both types of monomers and dimers known from the hexamer structure. All simulations were compared to previous ones of native insulin. DASI shows general similarity to the native simulations in most parts of the structure. Deviations are visible in the segments to which the bridge is directly connected, i.e. their flexibility is reduced. Upon removal of the bridge the ULKI simulations reapproach those of native insulin. The influence of the bridge spreads over the whole molecule, but all of its main structural features remain intact. The simulations suggest that the displacement of the C-terminal B chain of native insulin, considered important for receptor interaction, is prevented by the bridge, which also partially shields some binding residues. This is in accordance with the poor biological potency of A1-B29-crosslinked insulins.Abbreviations DASI-insulin(DASI) bovineN -^A1-N -^B29-di-aminosuberoyl insulin - ULK-insulin (ULKI) Native beef insulin with the bridge of DASI removed     

Diurnal rhythm of galanin-like immunoreactivity in the paraventricular and suprachiasmatic nuclei and other hypothalamic areas

The peptide galanin (GAL), when injected into the rat hypothalamus, is known to stimulate feeding behavior and affect the secretion of various hormones, including insulin and the adrenal steroid, corticosterone. To determine whether endogenous peptide levels shift in relation to natural rhythms of feeding and circulating hormone levels, rats were sacrificed at different times of the light/dark cycle, and their GAL levels were measured, via radioimmunoassay, in medial hypothalamic dissections and micropunched hypothalamic areas. The results suggest the existence of two distinct diurnal rhythms for hypothalamic GAL. One rhythm, detected exclusively in the area of the SCN, is characterized by bimodal peaks of GAL, threefold higher than basal peptide levels, around the onset of the dark and light periods. The second rhythm shows a single peak of GAL towards the middle of the nocturnal feeding cycle, specifically between the third and sixth hour. This latter rhythm is evident in the dorsal region of the medial hypothalamus, localized specifically to the lateral portion of the PVN. Moreover, it is inversely related to circulating insulin but unrelated to the adrenal steroids, suggesting a possible association between this pancreatic hormone and GAL in the PVN.