Biomedical subjects

W Zhang

Publications and source records attributed to W Zhang.

At least 883 records · Page 49Linked to original sources

PubMed1997

Constitutive signaling by the phototaxis receptor sensory rhodopsin II from disruption of its protonated Schiff base-Asp-73 interhelical salt bridge.

Sensory rhodopsin II (SRII) is a repellent phototaxis receptor in the archaeon Halobacterium salinarum, similar to visual pigments in its seven-helix structure and linkage of retinal to the protein by a protonated Schiff base in helix G. Asp-73 in helix C is shown by spectroscopic analysis to be a counterion to the protonated Schiff base in the unphotolyzed SRII and to be the proton acceptor from the Schiff base during photoconversion to the receptor signaling state. Coexpression of the genes encoding mutated SRII with Asn substituted for Asp-73 (D73N) and the SRII transducer HtrII in H. salinarum cells results in a 3-fold higher swimming reversal frequency accompanied by demethylation of HtrII in the dark, showing that D73N SRII produces repellent signals in its unphotostimulated state. Analogous constitutive signaling has been shown to be produced by the similar neutral residue substitution of the Schiff base counterion and proton acceptor Glu-113 in human rod rhodopsin. The interpretation for both seven-helix receptors is that light activation of the wild-type protein is caused primarily by photoisomerization-induced transfer of the Schiff base proton on helix G to its primary carboxylate counterion on helix C. Therefore receptor activation by helix C-G salt-bridge disruption in the photoactive site is a general mechanism in retinylidene proteins spanning the vast evolutionary distance between archaea and humans.

Amino Acid Sequence↗

PubMed1997

Binding of cationic (+4) alanine- and glycine-containing oligopeptides to double-stranded DNA: thermodynamic analysis of effects of coulombic interactions and alpha-helix induction.

Coulombic interactions and coupled conformational changes make important contributions to stability and specificity of many protein-nucleic acid complexes. As models of these phenomena in simpler systems, we have investigated the binding to mononucleosomal (160 base-pair) calf thymus DNA of a high charge density (compact) 5-residue (+4) oligopeptide (with 4 lysines and 1 tryptophan) and of four lower charge density (extended) 17-residue (+4) oligopeptides (each with 4 lysines, 10-12 alanines, 0-2 glycines, and 1 tryptophan). The fractional helicity (f(h)) of each oligopeptide before and after DNA binding was determined using circular dichroism. At low univalent cation concentration ([M+] = 6.4 mM), binding to DNA increases f(h) significantly for all but one of the extended oligopeptides. Oligopeptide-DNA binding constants (K(obs)) and apparent binding site sizes (n) were quantified using the noncooperative McGhee-von Hippel isotherm to fit tryptophan fluorescence quenching data. For each of the oligopeptides studied, n is found to be approximately equal to four, the number of lysine charges. In the range 6.4 mM < or = [M+] < or = 21.5 mM, power dependences of K(obs) on [M+] (SK(obs) = d log K(obs)/d log[M+]) for all 17-residue (+4) oligopeptides are similar with an average value of -3.7 +/- 0.4, which is indistinguishable (outside uncertainty) from the value obtained here for the compact (+4) oligopeptide and from values reported elsewhere for another compact tetralysine and for spermine (+4). Our results are consistent with the conclusion that the nonspecific binding to DNA of all these tetravalent ligands is driven primarily by coulombic interactions. At any [M+] investigated, values of K(obs) for the four extended (+4) oligopeptides differ by less than an order of magnitude, but all are 1-2 orders of magnitude less than values of K(obs) for two compact (+4) oligopeptides and for spermine. The differences in K(obs) for oligopeptide-DNA complexes, which all have similar n and similar SK(obs) indicate that when an extended oligopeptide binds to DNA it becomes more compact as a result of conformational changes, such as the additional alpha-helix formation detected by circular dichroism.

Alanine↗

PubMed1997

Sequential assignment and secondary structure determination for the Src homology 2 domain of hematopoietic cellular kinase.

The hematopoietic cellular kinase (Hck) is a member of the Src family of non-receptor protein-tyrosine kinases and participates in signal transduction events regulating the growth, differentiation and function of phagocytes. The secondary structure of the SH2 domain for Hck was determined for a 13C/15N-enriched sample using multi-dimensional NMR spectroscopy. The secondary structure for the domain was determined from chemical shift indices [1H alpha, 13C alpha and 13C'], sequential NOEs [d(alphaN)(i, i+1) and d(NN)(i, i+1)], and 3J(alphaN) scalar coupling constants. The Hck SH2 domain consists of two alpha-helices and seven beta-strands. Complementary strands of beta-sheets were identified from long-range NOEs using a novel 3D, 13C/15N-edited HMQC-NOESY-(HCACO)NH experiment that correlated 1H alpha resonances between beta-strands. The secondary structure for Hck SH2 is similar to that predicted from the sequence alignment of the Src-family protein tyrosine kinases.

Amino Acid Sequence↗

PubMed1997

5-HT inhibits calcium current and synaptic transmission from sensory neurons in lamprey.

In the lamprey spinal cord, 5-hydroxytryptamine (5-HT) immunoreactivity (ir) is present in the ventromedial plexus originating from intraspinal neurons, ventrolateral column arising from the brainstem, and dorsal column. The latter 5-HT system originates from small dorsal root ganglion neurons. Combined Lucifer yellow intracellular labeling of the intraspinal sensory neurons, dorsal cells, and 5-HT immunohistochemistry showed close appositions between 5-HT-ir fibers and dorsal cell axons. Application of 5-HT depressed monosynaptic EPSPs evoked in giant interneurons by stimulation of single dorsal cells, dorsal roots, or dorsal column without any detectable change in the input resistance of postsynaptic neurons. Furthermore, the amplitude of AMPA-evoked depolarizations in giant interneurons was unaffected by 5-HT. The lack of postsynaptic effects of 5-HT indicates that the decrease of the amplitude of sensory monosynaptic EPSPs by 5-HT is mediated by presynaptic mechanisms. The inhibition of monosynaptic EPSPs by 5-HT was not counteracted by an antagonist of 5-HT1A receptors. 5-HT also reduced the amplitude of the calcium current recorded in isolated dorsal cells and slowed down its kinetics. The inhibition of calcium channels could represent the mechanism mediating the depression of synaptic transmission at the axonal level. These results show that activation of 5-HT receptors on dorsal cell axons as well as on other sensory neurons mediates inhibition of sensory synaptic transmission to giant interneurons. In intact animals, 5-HT could be released from small 5-HT neurons in dorsal root ganglia, which thus may underlie direct sensory-sensory interactions.

8-Hydroxy-2-(di-n-propylamino)tetralin↗

PubMed1997

Decreased IGF-I gene expression during the apoptosis of Purkinje cells in pcd mice.

Insulin-like growth factor I (IGF-I) plays a potential functional role in cerebellar development in the rat, as indicated by its spatio-temporally coordinated expression with the IGF-I receptor (IGFR-I), IGF binding protein (IGFBP) 2 and 5 during the postnatal critical growth period. Although IGF-I promotes the survival of cultured cerebellar neurons, its role during cerebellar development in vivo is unclear. Growth factor deprivation has been shown to trigger apoptosis, the developmental cell death which, if abnormal, may lead to various pathological states. To understand the involvement of IGF-I in Purkinje cell survival, we examined mRNA expression of IGF-I, IGFR-I, IGFBP 2 and 5 in the Purkinje cell degeneration (pcd) mice. During pcd cerebellar development, Purkinje cells rapidly degenerate leading to their almost complete depletion by adult life. IGF system mRNA expression was studied during Purkinje cell death in the pcd mutants (pcd/pcd) at postnatal day (D) 11, 17, 24 and adult. At D11 and D17, no significant difference of the IGF-I system mRNA expression was observed between the normal and pcd/pcd cerebellum. At D24, a significant decrease of IGF-I mRNA was found in the apoptotic Purkinje cells in the pcd/pcd cerebellum, which was accompanied by a severe astrogliosis and activation of astrocytic IGF-I expression. In the adult pcd/pcd cerebellum, with few Purkinje cells remaining, many granule cells underwent apoptosis. In conclusion, decreased IGF-I mRNA expression was correlated with Purkinje cell apoptosis in pcd cerebellum. Whether the decrease of IGF-I mRNA expression is the cause or result of the Purkinje cell degeneration needs to be further elucidated.

Animals↗

PubMed1997

Solution NMR study of the structural basis of the Bohr effect in the monomeric hemoglobins from Chironomus thummi thummi.

The larva of the midge Chironomus thummi thummi possesses two monomeric hemoglobins. HbIII and HbIV, with extensive sequence homology, which exhibit marked but differential Bohr effects (pH influence on ligand affinity). These Hbs serve as ideal models for allosteric control of ligand affinity via tertiary-only structural changes. The cyanomet derivatives of these two Hbs have been shown to possess essentially indistinguishable heme cavity structures in solution at low pH (Zhang et al., 1996) that are also very similar to that of the low pH form of HbIII in the crystal (Steigemann & Weber, 1979). 2D 1H NMR has been utilized to elucidate the solution heme cavity structure of the alkaline form of the cyanomet derivatives of HbIII and HbIV to identify the Bohr proton binding site and characterize the nature of the structural changes that accompany the allosteric transition. Significant structural changes with pH have been identified in two regions of the heme cavity, near the axial His and at the junction of pyrroles B and C. The Bohr proton site is identified as His94, which at low pH makes a salt bridge to the terminal Met136. The rupture of this salt bridge at high pH leads to the expulsion of the Met136 side chain next to the His F8 ring where it serves as a spacer between the heme and F-helix, and leads to a cascade of side chain reorientations in the densely packed hydrophobic interior involving five Phe (65, 66, 128, 129, 133), Val132, and Ile69, all on the E- and H-helices. The terminal member of the cascade, Phe65, which acts as a spacer between the E- and F-helices at low pH, is rotated toward the heme plane. The conversion of the low pH, low-affinity "tense" to the high pH, high-affinity "relaxed" state is primarily due to the removal of the Met136 and Phe65 spacers. A central residue in transmitting the Bohr effect from His94 to Phe65 is residue 132. In HbIV, Val132 provides a cavity in the hydrophobic core to readily accommodate the initial step in rotating the Phe129 side chain. In HbIII, the Ile132 provides tight packing to all neighboring side chains and hence would inhibit the rotation of the Phe129 side chain. It is proposed that the lone internal residue difference between HbIII (Ile132) and HbIV (Val132) is the primary basis for the different amplitudes of their Bohr effect.

Allosteric Regulation↗

PubMed1997

Solution of 1H NMR structure of the heme cavity in the oxygen-avid myoglobin from the trematode Paramphistomum epiclitum.

A two-dimensional 1H NMR study has been carried out on the heme cavity of the extreme oxygen-avid and autoxidation-resistant oxy-myoglobin complex from the trematode Paramphistomum epiclitum, and the residues were identified which potentially provide hydrogen bond stabilization for the bound oxygen. Complete assignment of the heme core resonances allows the identification of 10 key heme pocket residues, 4 Phe, 4 Tyr, and 2 upfield ring current aliphatic side chains. Based solely on the conserved myoglobin folding topology that places the E helix-heme crossover and the completely conserved Phe(CD1)-heme contact at opposing meso positions, the heme orientation in the cavity and the E helix alignment were unambiguously established that place Tyr66 at position E7. Moreover, all eight aromatic and the two aliphatic side chains were shown to occupy the positions in the heme cavity predicted by amino acid sequence alignment with globins of known tertiary structure. The dipolar contacts for the Tyr32(B10) and Tyr66(E7) rings indicate that both residues are oriented into the heme cavity, which is unprecedented in globins. The ring hydroxyl protons for both Tyr are close to each other and in a position to provide hydrogen bonds to the coordinated oxygen, as supported by strong retardation of their exchange rate with bulk solvent. A more crowded and compact structure increases the dynamic stability of the distal pocket and may contribute to the autoxidation resistance of this myoglobin.

Amino Acid Sequence↗

PubMed1997

Inhibition of the growth of WI-38 fibroblasts by benzyloxycarbonyl-Leu-Leu-Tyr diazomethyl ketone: evidence that cleavage of p53 by a calpain-like protease is necessary for G1 to S-phase transition.

The effect of a calpain-selective cell permeant inhibitor, benzyloxycarbonyl Leu-Leu-Tyr diazomethylketone (ZLLY-CHN2), on the serum-stimulated growth of WI-38 human fibroblasts has been investigated. Only cell permeant protease inhibitors with activity against calpains prevented progression into S-phase. Protein blotting experiments indicated that p53 immunoreactivity increased in late G1 cells treated with ZLLY-CHN2. The content of p21Waf1/Cip1 CDK inhibitor also increased, providing a mechanism for the observed failure to enter S-phase. Further studies indicated that p53 could be degraded by a ZLLY-CHN2-sensitive protease immediately prior to S-phase, but that proteolysis did not occur after this critical time point. Chelation of extracellular Ca2+ by addition of EGTA inhibited the p53 degradation. Consistent with proteolysis of p53 in late G1 phase, mu-calpain immunoreactivity transiently accumulated in cell nuclei at this time. ZLLY-CHN2 did not appear to increase p53 mRNA in WI-38 cells. Purified mu-calpain required only 1 to 3 microM Ca2+ to proteolyze p53 in WI-38 cell lysates. These results indicate that ZLLY-CHN2 inhibits progression of WI-38 cells into S-phase by inactivating a calpain-like protease that is responsible for proteolysis of constitutively expressed p53 in late G1.

Calcium↗

PubMed1997

Involvement of endogenous orphanin FQ in electroacupuncture-induced analgesia.

Recent studies suggest that the novel opioid peptide orphanin FQ (OFQ) is involved in pain modulation. We found that intracerebroventricular (i.c.v.) administration of OFQ in the rat produced a dose-dependent antagonism of the analgesia induced by 100 Hz electroacupuncture (EA) stimulation as measured in the radiant heat tail-flick assay. Antisense oligonucleotides injected i.c.v. potentiated EA analgesia, presumably by interfering with the expression of the OFQ receptor in brain. These results suggest that endogenous OFQ exerts a tonic antagonistic effect on EA-induced analgesia. No such antagonism was observed when OFQ was injected intrathecally (i.t.). Rather, it appears that spinal OFQ produced a marked analgesic effect and enhanced EA-induced analgesia. These findings are consistent with the experimental results obtained in rats where morphine-induced analgesia is antagonized by i.c.v. OFQ and potentiated by i.t. OFQ.

Analgesia↗

PubMed1997

Intraoperative ultrasound-guided transhepatic lithotomy. A new alternative surgical procedure for the management of residual hepatic stones.

BACKGROUND: The high incidence of residual stones has been a major problem in the treatment of hepatolithiasis. Although various imaging techniques have been used to locate the stones, and many different postoperative procedures have been used as remedial modalities to remove the residual calculi, results have been far from satisfactory. OBJECTIVES: To remove obstinate hepatic stones and reduce the incidence of residual calculi. DESIGN: Prospective clinical trial. SETTING: Medical university-affiliated hospital. PATIENTS AND METHODS: Ten patients who had residual intrahepatic stones after conventional operative procedures underwent intraoperative ultrasound (IOUS)-guided transhepatic lithotomy between July 1988 and July 1995. This surgical technique includes accurately locating stones with IOUS, choosing a surgical approach path under the guidance of IOUS while avoiding critical blood vessels and uninvolved biliary tracts, dividing hepatic parenchyma to the involved biliary ducts, and removing the obstinate calculi using the real-time image of IOUS, which is able to monitor the movement of the lithotomy instruments without interruption. MAIN OUTCOME MEASURES: Clinical practical value of IOUS-guided transhepatic lithotomy in the treatment of residual hepatic stones. RESULTS: Complete removal of the stones was achieved in all 10 patients. There were no severe complications or mortality at a median follow-up of 39 months. CONCLUSIONS: IOUS-guided transhepatic lithotomy can greatly decrease the incidence of residual hepatic stones. It is accurate and safe. As a new surgical procedure, IOUS-guided transhepatic lithotomy should be an alternative modality in the management of hepatolithiasis, although the long-term benefits still need to be observed.

Adult↗

PubMed1997

Lack of effect of long-term fluoride ingestion on blood chemistry and frequency of sister chromatid exchange in human lymphocytes.

Two studies were conducted to assess the potential for adverse physiologic and genotoxic effects of long-term fluoride ingestion in adults residing in three communities with varying water fluoride levels (0.2 ppm, 1.0 ppm, and 4.0 ppm). All were long-time (> or = 30 years) residents of their respective communities. Plasma and urine samples were collected for fluoride analyses. Additional plasma was collected to determine blood chemistry, and plasma lymphocytes were examined to determine the frequency of sister chromatid exchange. Significant differences in urine (P = 0.001) and plasma (P = 0.0001) fluoride levels were found in the three communities. Seven of the blood parameters were statistically different among the communities, although all were within the defined normal range of the pathology laboratory. Sister chromatid exchange frequency was statistically higher in the 4.0 ppm fluoride community as compared to the other communities. Because of the higher SCE frequency in the 4.0 ppm fluoride community, a second study was performed to determine if the increased frequency was potentially related to the fluoride level of the communal water supply. Of the 58 adults recruited; 30 had used city water and 28 had used well water (< or = 0.3 ppm fluoride) as their principal water source for 30 years. Data analyses showed that the sister chromatid exchange frequency did not differ between the groups, indicating that the increased sister chromatid exchange frequency was not related to the fluoride level of the communal water. The investigation provided evidence that the long-term ingestion of water containing 4.0 ppm fluoride did not have any clinically important physiologic or genotoxic effects in healthy adults.

Adult↗

PubMed1997

Capillary electrophoretic separation of tricyclic antidepressants using charged carboxymethyl-beta-cyclodextrin as a buffer additive.

Charged carboxymethyl-beta-cyclodextrin was successful in the capillary electrophoretic separation of a series of tricyclic antidepressants. The cyclodextrin alone was successful in the separation of carbamazepine, protriptyline, desipramine, clomipramine, and opipramol using a 3-(trimethoxysilyl)propyl methacrylate capillary coating to reduce the electroosmotic flow. The ideal buffer pH was found to be in the range of 6-7 and the ideal cyclodextrin concentration to be 10 mM. All nine antidepressants were resolved using the charged cyclodextrin in the micellar electrokinetic chromatography (MEKC) mode with sodium dodecyl sulfate as the surfactant. Neither the cyclodextrin nor the surfactant alone were successful in resolving the whole series of compounds under investigation but a combination of both produced the separation. Separations were performed on a linear polyacrylamide coated capillary. The ideal pH of the buffer was in the range of 5-7.

Antidepressive Agents, Tricyclic↗

PubMed1997

Estimation of water extraction fractions in rat brain using magnetic resonance measurement of perfusion with arterial spin labeling.

The model used for calculating perfusion by MRI techniques that use endogenous water as a tracer assumes that arterial water is a freely diffusible tracer. Evidence shows that this assumption is not valid in the brain at high blood flow rates, at which movement of water into and out of the microvasculature becomes limited by diffusion across the blood-brain barrier. In this work, the arterial spin-labeling technique is used to show that fraction of arterial water that is dependent on blood flow rate remains in the vasculature and does not exchange with brain tissue water. By using perfusion measurements without and with magnetization transfer (MT) effects, one can distinguish arterial label that exchanges into tissue because blood has much smaller MT than brain tissue. Using this technique, the extraction fraction for water is measured in the rat brain at various cerebral blood flow rates. At high flow rates (approximately 5 ml/g/min), the extraction fraction for water is found to be about 45% in rat brain. Disruption of the blood-brain barrier with D-mannitol caused an increase in the extraction fraction for water. It was possible to form an image related to the extraction fraction for water. The ability to estimate the amount of vascular water exchanging with tissue water by MRI may represent a noninvasive approach to detect the integrity of the blood-brain barrier.

Animals↗

PubMed1997

Diabetes-induced apoptosis in rat kidney.

Oxidative stress has been suggested to play a crucial role in the pathogenesis of diabetic complications including nephropathy. However, the exact mechanism of diabetic nephropathy is still not clearly understood. Since oxidative stress in known to be a major component in the induction of apoptosis, we investigated the occurrence of apoptosis in diabetic rat kidney. The status of oxidative stress was determined as thiobarbituric acid reactive substances (TBARS). The TBARS in the control and diabetic rat kidney were 2.00 +/- 0.963 and 3.83 +/- 0.715 mumol/mg protein, respectively (P < 0.05). Apoptosis was determined by evaluating the DNA fragmentation using an enzyme-linked immunoassay and in situ end labeling. DNA fragmentation increased approximately fourfold in diabetic rat kidney compared to the normal kidney (P < 0.05). Apoptag in situ labeling displayed negligible apoptosis in nondiabetic kidney while significant areas of apoptosis were observed in diabetic kidney. Our results suggest that increased oxidative stress in diabetic kidney could induce apoptosis, which may contribute to the development of diabetic nephropathy.

Animals↗

PubMed1997

Regulation of ion transport by P2u purinoceptors and alpha 2A adrenoceptors in HT29 cells.

X-ray microanalysis was applied to investigate ion transport mediated by P2U purinoceptors and alpha 2A adrenoceptors as well as their interaction in the regulation of the intracellular elemental concentration in HT29 cells. In response to ATP, HT29 cells showed a decrease of intracellular Cl, Na and an increase in Ca. A similar result was observed with UTP, but UTP appeared to be more potent than ATP. On the other hand, UK14,304, an alpha 2 receptor agonist, was found to be capable of reversing the action of both UTP and ATP on ion secretion, and caused a clear increase in intracellular Na and Cl. Moreover, treatment of cells with UK14,304 before exposure to UTP did not induce a decrease in Cl and Na, suggesting that UK14,304 blocks the action of UTP. The secretory effect of UTP was also blocked by NPPB, a chloride channel blocker, and alloxan. Chelation of extracellular Ca with EGTA abolished ion response to UTP. These results suggest that since inhibition of the intracellular cAMP system and chelation of Ca2+ can block the nucleotide-induced chloride secretion, the ATP and UTP-induced chloride secretion can be mediated via both cAMP-dependent and Ca(2+)-dependent pathways.

HT29 Cells↗

PubMed1997

The C1q-binding cell membrane proteins cC1q-R and gC1q-R are released from activated cells: subcellular distribution and immunochemical characterization.

Two types of widely coexpressed cell surface C1q-binding proteins (C1q-R): a 60-kDa calreticulin-homolog which binds to the collagen-like "stalk" of C1q and a 33-kDa protein with affinity for the globular "heads" of the molecule, have been described. In this report, we show that the two molecules are also secreted by Raji cells and peripheral blood lymphocytes and can be isolated in soluble form from serum-free culture supernatant by HPLC purification using a Mono-Q column. The two purified soluble proteins had immunochemical and physical characteristics similar to their membrane counterparts in that both bound to intact C1q and to their respective C1q ligands, cC1q and gC1q. In addition, N-terminal amino acid sequence analyses of the soluble cC1q-R and gC1q-R were found to be identical to the reported sequences of the respective membrane-isolated proteins. Ligand blot analyses using biotinylated membrane or soluble cC1q-R and gC1q-R showed that both bind to the denatured and nondenatured A-chain and moderately to the C-chain of C1q. Moreover, like their membrane counterparts, the soluble proteins were found to inhibit serum C1q hemolytic activity. Although cC1q-R was released when both peripheral blood lymphocytes and Raji cells were incubated in phosphate-buffered saline for 1 hr under tissue culture conditions, gC1q-R was releasable only from Raji cells, suggesting that perhaps activation or transformation leading to immortalization is required for gC1q-R release. Subcellular fractionation of Raji cells and analyses by enzyme-linked immunosorbent assay and Western blotting showed that the two molecules are present in the cytosolic fractions as well as on the membrane. The data suggest that soluble forms of both C1q-binding molecules are released from cells and that these molecules may play important roles in vivo as regulators of complement activation.

Amino Acid Sequence↗

PubMed1997

Enhanced permeability of freeze-dried liposomal bilayers upon rehydration.

Until now, studies on the protection of liposomes against freeze-drying damage have mainly focused on the bilayer integrity during the freezing or drying step of this process. Here, we investigated the bilayer permeability of freeze-dried, lyoprotected liposomes to a nonbilayer interacting compound after rehydration, by monitoring the leak-in kinetics of externally added carboxyfluorescein (CF). The results showed that freeze-drying and rehydration of DPPC:DPPG 10:1 liposomes with sucrose in- and outside the vesicles caused a temporary increase in the bilayer permeability for CF, which leveled off after approximately 20 h. The amount of CF/mol phospholipid which leaked into the vesicles increased with vesicle size (range 0.1-1 micro m) / lamellarity. Reduction of the number of bilayers in 1-1 micro m) vesicles enhanced the permeability to CF after freeze-drying and rehydration. The presence of CHOL decreased CF leak-in rates into 1 micro m MLVs consisting of DPPC:DPPG 10:1, but not into 0.1-micro m unilamellar vesicles. In the absence of sucrose similar leak-in profiles as a function of time were found after rehydration, suggesting that repacking processes of the bilayer were responsible for the enhanced permeability after freeze-drying and dehydration both with and without sucrose. The effect of size and lamellarity on the CF leak-in correlated with the retention of encapsulated CF after freeze-drying and rehydration, but no correlation was found with the effect of lipid composition. Both small (0.1 micro m) lyoprotected liposomes made of DPPC:DPPG 10:1 and DPPC:DPPG:CHOL 10:1:4 were highly permeable during the rehydration step itself. The results indicate that, despite the presence of the lyoprotectant, "repacking" of the bilayer components takes place both during and after rehydration. This eventually leads to regaining of its barrier function.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1997

Influence of distal nerve segment volume on nerve regeneration in silicone tubes.

The influence of a volume of a distal nerve segment upon nerve regeneration in an 8-mm gap created within a silicone tube was examined. The rats were randomly divided into four groups. Each group had 5 mm, 1 mm, or a half volume of 1-mm nerve segment (a nerve piece of 1 mm transected longitudinally) inserted into the distal end of a silicone tube of 11 mm. The empty group without a nerve segment was used as control. Diameters of regenerated cylindrical structure between the nerve ends in the silicone tube were measured under an operation microscope and myelinated axon diameter, myelinated axon density, myelin sheath width, and ratio of myelinated axon area to total cross sectional area were measured using the transverse sections at the midpoint of the silicone tube at 6 weeks after surgery. Although there was a significant difference in all of those parameters between the control group and any of the remaining three groups, no significant difference was found between any pair of these three groups. The results of this study indicated that the degree of nerve regeneration does not correlate with the volume of a distal nerve segment and even a very small piece can play an important role in supporting regenerating nerve beyond a definitive gap.

Animals↗