Interferon beta-1b modulates serum sVCAM-1 levels in primary progressive multiple sclerosis

Endothelial activation is a key feature of multiple sclerosis (MS) pathogenesis. It is modulated by interferon beta-1b (IFNB-1b) treatment in relapsing-remitting MS (RRMS) patients. This particular pharmacodynamic effect still has to be proven in primary progressive MS (PPMS). In the current study, serum concentrations of soluble vascular cell adhesion molecule-1 (sVCAM-1) and sE-selectin were analyzed longitudinally in 18 PPMS patients before, during and after 12 months of treatment with IFNB-1b. During drug therapy there was a significant early and sustained increase of sVCAM-1 (overall P < 0.0001). Flu-like symptoms induced by IFNB-1b and also concomitant infections were associated with higher sVCAM-1 levels. Neutralizing antibodies to IFNB-1b were associated with lower sVCAM-1 levels. In conclusion, IFNB-1b modulates the adhesion cascade in patients with PPMS in a similar way it does in RRMS. Nevertheless, a clinical effect of IFNB in PPMS still has to be proven in a randomized controlled clinical trial.

Membrane phospholipid composition affects function of potassium channels from rabbit colon epithelium

We tested the effects of membrane phospholipids on the function of high-conductance, Ca(2+)-activated K(+) channels from the basolateral cell membrane of rabbit distal colon epithelium by reconstituting these channels into planar bilayers consisting of different 1:1 mixtures of phosphatidylethanolamine (PE), phosphatidylcholine (PC), phosphatidylserine (PS), and phosphatidylinositol (PI). At low ambient K(+) concentrations single-channel conductance is higher in PE/PS and PE/PI bilayers than in PE/PC bilayers. At high K(+) concentrations this difference in channel conductance is abolished. Introducing the negatively charged SDS into PE/PC bilayers increases channel conductance, whereas the positively charged dodecyltrimethylammonium has the opposite effect. All these findings are consistent with modulation of channel current by the charge of the lipid membrane surrounding the channel. But the K(+) that permeates the channel senses only a small fraction of the full membrane surface potential of the charged phospholipid bilayers, equivalent to separation of the conduction pathway from the charged phospholipid head groups by 20 A. This distance appears to insulate the channel entrance from the bilayer surface potential, suggesting large dimensions of the channel-forming protein. In addition, in PE/PC and PE/PI bilayers, but not in PE/PS bilayers, the open-state probability of the channel decreases with time ("channel rundown"), indicating that phospholipid properties other than surface charge are required to maintain channel fluctuations.

Insertion of EspD into epithelial target cell membranes by infecting enteropathogenic Escherichia coli

Diffusely adhering Escherichia coli (DAEC) strains have been implicated in epidemiological studies as a cause of diarrhoea in children. However, the molecular interactions of these pathogens with target cells have remained largely obscure. We found that some DAEC strains contain homologues of the locus of enterocyte effacement (LEE) pathogenicity island and secrete EspA, EspB and EspD proteins necessary for the formation of the attaching and effacing (A/E) lesions. To characterize the function of the EspD protein further, we cloned and sequenced the espD genes of two DA-EPEC strains and compared their deduced amino-acid sequences with known EspD sequences. A pattern of two conserved transmembrane regions and one conserved coiled-coil region is predicted in EspD and also in the type III system secreted proteins YopB, PopB, IpaB and SipB of Yersinia, Pseudomonas, Shigella and Salmonella respectively. The EspD protein is inserted into a trypsin-sensitive location in the HeLa cell membrane at sites of bacterial contact, but is not translocated into the cytoplasm. Secretion of EspD increases upon contact with host cells. We propose that the membrane-located EspD protein is part of the translocation apparatus for Esp proteins into the target host cell performing functions similar to YopB in Yersinia.

Diffusely adhering Escherichia coli strains induce attaching and effacing phenotypes and secrete homologs of Esp proteins

Recent epidemiological studies indicate that Escherichia coli strains which exhibit the diffuse-adherence phenotype (DAEC strains) represent a potential cause of diarrhea in infants. We investigated the interaction of DAEC strains isolated from diarrhea patients in Brazil and in Germany with epithelial cells in tissue culture. The investigated strains were identified as DAEC strains by (i) their attachment pattern, (ii) presence of genes associated with the Dr family of adhesins, and (iii) lack of genetic markers for other diarrhea-associated E. coli categories. Several clinical DAEC isolates were shown to secrete similar patterns of proteins into tissue culture medium. Protein secretion was found to be regulated by environmental parameters, namely, medium, temperature, pH, and iron concentration. DAEC strains secreting these proteins induced accumulation of actin and tyrosine-phosphorylated proteins at sites of bacterial attachment, leading to the formation of pedestals and/or extended surface structures. These changes were phenotypically similar to the attaching and effacing (A/E) lesions observed with enteropathogenic and some enterohemorrhagic E. coli strains carrying the locus of enterocyte effacement (LEE) pathogenicity island. Proteins homologous to the EspA, EspB, and EspD proteins, necessary for signal transduction events inducing A/E lesions, were identified by sequence analysis and cross-reaction of specific antibodies. However, initially nonadhering strains secreting these proteins induced signal transduction events only after prolonged infection. These results indicate that secretion of the Esp proteins alone is not sufficient for efficient signal transduction. This study further shows that some DAEC strains are likely to contain a homolog(s) of the LEE locus which may contribute to the pathogenic potential of DAEC.

Differential expression of c-fos messenger RNA in the rat spinal cord after mucosal and serosal irritation of the stomach

Expression of the immediate early gene c-fos is considered to be a marker for neuronal activation in the spinal cord in response to afferent input. Since the stomach is continually exposed to injurious chemicals, the present study examined whether application of acid (0.15 M HCl) and formalin (5%) to the gastric mucosa or serosal surface of the stomach stimulates c-fos transcription in the caudal thoracic spinal cord of anaesthetized rats. The spinal cord was removed 15, 45 or 120 min after exposure of the stomach to the noxious chemicals and processed for quantitative in situ hybridization autoradiography of c-fos messenger RNA. Exposure of the gastric mucosa to acid or formalin failed to increase the expression of c-fos messenger RNA in the thoracic spinal cord. Application of acid to the serosal surface of the stomach was also unable to stimulate c-fos transcription, whereas serosal application of formalin led to substantial expression of c-fos messenger RNA in the superficial but also deeper laminae of the spinal dorsal horn when examined 45 min, but not 15 or 120 min, post-stimulation. The highest expression of c-fos messenger RNA was seen when formalin was injected subcutaneously into one hindpaw and c-fos transcription was examined in the lumbar spinal cord. These data indicate that acute exposure of the gastric mucosa to chemical injury does not provide the afferent input which is necessary to cause appreciable c-fos transcription in second order neurons within the spinal cord. Stimulation of the gastric mucosa by acid and formalin was followed, however, by gastric hyperaemia in which spinal afferents releasing vasodilator peptides have been implicated. It is concluded, therefore, that acute stimulation of nociceptive afferents in the stomach causes local homoeostatic reactions but does not necessarily provide afferent input sufficient to recruit spinal nociceptive circuits.

Inhibition of high-conductance, calcium-activated potassium channels of rabbit colon epithelium by magnesium

High-conductance, Ca(2+)-activated K+ channels from the basolateral membrane of rabbit distal colon epithelial cells were reconstituted into planar phospholipid bilayers to examine the effect of Mg2+ on the single-channel properties. Mg2+ decreases channel current and conductance in a concentration-dependent manner from both the cytoplasmic and the extracellular side of the channel. In contrast to other K+ channels, Mg2+ does not cause rectification of current through colonic Ca(2+)-activated K+ channels. In addition, cytoplasmic Mg2+ decreases the reversal potential of the channel. The Mg(2+)-induced decrease in channel conductance is relieved by high K+ concentrations, indicating competitive interaction between K+ and Mg2+. The monovalent organic cation choline also decreases channel conductance and reversal potential, suggesting that the effect is unspecific. The inhibition of channel current by Mg2+ and choline most likely is a result of electrostatic screening of negative charges located superficially in the channel entrance. But in addition to charge, other properties appear to be necessary for channel inhibition, as Na+ and Ba2+ are no (or only weak) inhibitors. Mg2+ and possibly other cations may play a role in the regulation of current through these channels.

Morphologic basis of the functional gastric acid barrier

The gastric mucosa possesses a functional barrier that prevents intrusion of luminal acid. The aim of the present study was to elucidate the morphologic basis of this barrier by exploring the effect of acid challenge on the gastric mucosal epithelium, basal lamina, and microvasculature. The stomachs of urethane-anesthetized rats were perfused, for at least 45 minutes, with 0.05 M HCl or 0.15 M HCl in the absence or presence of the mucosal barrier breaker ethanol (15%) and examined by light, scanning, and transmission electron microscopy. Gastric perfusion with 0.05 M HCl alone caused superficial cell injury, the damaged surface cells loosing the surface membrane, whereas the junctional complex and basolateral membrane were preserved. Perfusion of 0.15 M HCl alone led to focal ablation of surface epithelial cells in the interfoveolar regions, and cells in the gastric pits remained grossly normal. Exposure to the barrier breaker ethanol (15%) in the presence of 0.05 M HCl caused extensive ablation of the surface epithelium. There were many focal areas in which the honeycomb structure of the lamina propria was exposed and the basal lamina was removed. Gastric mucosal damage progressed further when the luminal HCl concentration was raised to 0.15 M in the presence of ethanol (15%). In this instance, extensive areas with deep erosions and vast areas of deep-reaching ablation of the epithelium and basal lamina were observed. Ultrastructurally, there was extensive damage to the endothelium of capillaries lying underneath denuded areas of the gastric mucosa, the injured capillaries containing erythrocyte ghosts and thrombocyte aggregates. The data suggest that the integrity of the junctional complex, basolateral membrane, and basal lamina forms the morphologic basis of the functional gastric acid barrier. Once these structures are disrupted or ablated to an appreciable extent, damage forms in the mucosal microvasculature, and injury progresses to deeper layers of the mucosa.

Visceral vasodilatation and somatic vasoconstriction evoked by acid challenge of the rat gastric mucosa: diversity of mechanisms

1. Acid back-diffusion through a disrupted gastric mucosal barrier increases blood flow to the stomach without any change in systemic blood pressure. This study was undertaken to examine the gastric acid-evoked changes in blood flow in a number of visceral and somatic arterial beds and to elucidate the mechanisms which lead to the regionally diverse haemodynamic responses. 2. The gastric mucosa of urethane-anaesthetized rats was challenged with acid by perfusing the stomach with ethanol (15%, to disrupt the gastric mucosal barrier) in 0.15 M HCl. Blood flow was estimated by laser Doppler flowmetry, the hydrogen clearance method or the ultrasonic transit time shift technique. 3. Gastric acid challenge increased blood flow in the gastric mucosa and left gastric artery while blood flow in the femoral artery and skin declined. 4. Afferent nerve stimulation by intragastric administration of capsaicin enhanced blood flow in the left gastric artery but did not diminish blood flow in the femoral artery when compared with the vehicle. 5. The gastric acid-evoked dilatation of the left gastric artery was depressed by acute extrinsic denervation of the stomach, capsaicin-induced ablation of afferent neurones or hexamethonium-induced blockade of autonomic ganglionic transmission. 6. The gastric acid-induced constriction of the femoral artery was attenuated by acute extrinsic denervation of the stomach but left unaltered by capsaicin, hexamethonium, guanethidine, indomethacin, telmisartan (an angiotensin II antagonist), [d(CH2)5(1), Tyr(Me)2, Arg8]-vasopressin (a vasopressin antagonist), bosentan (an endothelin antagonist) and acute ligation of the blood vessels to the adrenal glands. 7. These data show that acid challenge of the gastric mucosa elicits visceral vasodilatation and somatic vasoconstriction via divergent mechanisms. The gastric hyperaemia is brought about by extrinsic vasodilator nerves, whereas the reduction of somatic blood flow seems to be mediated by non-neural, probably humoral, vasoconstrictor messengers that remain to be identified.

Diverse interactions of calcitonin gene related peptide and nitric oxide in the gastric and cutaneous microcirculation

Calcitonin gene related peptide (CGRP) is the major mediator of afferent nerve mediated vasodilatation in the gastric mucosa and skin of the rat. Since receptors for CGRP occur on both the vascular endothelium and smooth muscle, it is conceivable that the vascular actions of CGRP involve multiple mechanisms. The vasodilator effect of rat CGRP-alpha in the rat gastric mucosa is indeed inhibited by blockage of nitric oxide (NO) synthesis, as is the gastric mucosal hyperemia in response to gastric acid challenge, which is mediated by CGRP release from afferent nerve fibres. In contrast, the vasodilator response to rat CGRP-alpha in the rat hind paw and the CGRP-mediated vasodilatation evoked by antidromic stimulation of afferent nerve fibres do not depend on the formation of NO. These data indicate that NO plays regionally different roles in the local vasodilator action of CGRP. NO is a secondary vasorelaxant messenger of CGRP in the gastric, but not in the cutaneous, microcirculation. However, this L-arginine-derived autacoid may have a role in the irritant-induced CGRP release from afferent vasodilator fibres in the skin.

Sensory nerves, nitric oxide and NANC vasodilatation

Primary afferent neurons, originating from the dorsal root ganglia, provide a perivascular network of fibres around the arterial system throughout the body. When stimulated, these fibres cause a nonadrenergic noncholinergic (NANC) vasodilatation by release of calcitonin gene-related peptide (CGRP). This peptide is a potent vasodilator and, in this action, cooperates with nitric oxide (NO) in a tissue-specific manner. The hyperaemic effect of intravascularly injected rat CGRP-alpha in the rat gastric mucosa is reduced by blockade of the NO synthesis, which indicates that CGRP dilates the gastric microvascular bed via NO-dependent and -independent mechanisms. This is also true for endogenous CGRP, as the gastric mucosal hyperaemia, which is caused by gastric acid challenge and involves CGRP, is likewise blocked by inhibition of the NO synthesis. The CGRP/NO-mediated vasodilatation is an important element of a neural emergency system that strengthens the resistance of the gastric mucosa in the face of pending acid injury. In the rat skin, CGRP participates in neurogenic inflammatory processes but the cutaneous vasodilator action of exogenous CGRP and the CGRP-mediated vasodilatation, evoked by antidromic stimulation of afferent nerve fibres, do not depend on the formation of NO. This L-arginine-derived autacoid, however, plays a role in the release of CGRP from afferent nerve fibres in the skin since it contributes to the CGRP-mediated vasodilator responses to chemical irritation or immunological challenge via interleukin-1 beta. These data indicate that the type of interaction between CGRP and NO in causing a NANC vasodilatation varies with the vascular bed under study. Depending on the tissue, NO may facilitate the release of CGRP from afferent nerve fibres or be a secondary vasorelaxant messenger of the peptide.

Vascular bed-dependent roles of the peptide CGRP and nitric oxide in acid-evoked hyperaemia of the rat stomach

1. Acid back-diffusion through a disrupted gastric mucosal barrier is known to increase gastric mucosal blood flow via a neural mechanism. The present study examined how the acid-evoked change in the gastric microcirculation compares with blood flow changes in the left gastric artery, one of the major arteries supplying the stomach, and whether the dilator mediators in the left gastric artery are identical to those in the gastric mucosa. 2. The experiments were performed on rats anaesthetized with urethane. Blood flow in the left gastric artery was measured by the ultrasonic transit time shift technique, and blood flow in the gastric mucosa was assessed by the hydrogen gas clearance method. 3. Gastric acid back-diffusion evoked by perfusion of the stomach with 15% ethanol in 0.15 M HCl increased blood flow in the left gastric artery by a factor of 4.7, which was significantly larger than the 2.9-fold increase in blood flow through the gastric mucosa. Blood pressure and heart rate were not altered appreciably. 4. The acid-evoked hyperaemia in the left gastric artery was left unaltered by atropine and the substance P receptor antagonist RP-67580. 5. The calcitonin gene-related peptide (CGRP) antagonist CGRP (8-37) had no effect on gastric blood flow but prevented the dilator action of CGRP and inhibited the acid-evoked hyperaemia in the gastric mucosa to a larger degree than the hyperaemia in the left gastric artery. 6. Blockade of nitric oxide synthesis by N omega-nitro-L-arginine methyl ester (L-NAME) caused constriction of the left gastric artery and the gastric mucosal microvessels. The acid-evoked vasodilatation in the gastric mucosa was blocked by L-NAME, whereas the dilator response in the left gastric artery was not significantly depressed. 7. The data show that the gastric hyperaemic response to acid back-diffusion results from dilatation of mucosal microvessels and extramural arteries. The dilator mechanisms, however, differ between the two vascular beds. CGRP and nitric oxide are important vasodilator mediators in the gastric mucosa but are of less relevance in the left gastric artery.

Neurogenic chloride secretion induced by scorpion venom and veratrine in rabbit colon

In earlier reconstitution experiments the venom of the scorpion Leiurus quinquestriatus, LQV, was shown to block Ca(2+)-activated high-conductance K+ channels from the basolateral cell membrane of rabbit colonocytes (Turnheim K, Costantin J, Chan S, Schultz SG (1989) J Membrane Biol 112:247-254). These LQV-sensitive K+ channels do not seem to be involved in active Na+ transport across rabbit colon, as absorptive Na+ fluxes were not significantly affected by serosal addition of LQV to isolated epithelia of rabbit descending colon. While Na+ absorption was not changed, LQV and veratrine caused electrogenic Cl- secretion in this tissue by a neural (tetrodotoxin sensitive) mechanism. The secretory effect of LQV was partly inhibited by atropine, suggesting the involvement of m-cholinoceptors, and by a VIP-antagonist. In contrast to the neurogenic secretion in the small intestine of guinea pig, rat and cat, 5-hydroxytryptamine (5-HT) does not seem to be involved in neurogenic secretion in rabbit colon, as 1) several 5-HT receptor antagonists did not inhibit the LQV effect with the exception of high concentrations of tropisetron, 2) exogenous 5-HT had no secretory effect, and 3) there was no significant release of 5-HT from the tissue during neurogenic secretion. The inhibitory effect of tropisetron on intestinal Cl- secretion seems to be unrelated to its property as a 5-HT3 receptor antagonist.

Yeast mitochondria lacking the two import receptors Mas20p and Mas70p can efficiently and specifically import precursor proteins

Mas20p and Mas70p are integral proteins of the yeast mitochondrial outer membrane that appear to function as receptors for precursor proteins imported from the cytosol. Loss of either receptor alone does not block import or kill the cells, but deletion of Mas20p causes loss of respiration (Ramage, L., Junne, T., Hahne, K., Lithgow, T., and Schatz, G. (1993) EMBO J. 12, 4115-4123). Here we show that this respiratory deficiency is only temporary; given time to adapt, virtually all cells lacking MAS20p regain respiration without regaining MAS20p. The respiratory defect can also be suppressed (at a frequency of about 10(-6)) by a dominant mutation of a single nuclear gene. The suppressed cells, unlike the unsuppressed ones, tolerate disruption of the MAS70 gene. The resulting double disruptants lack both Mas20p and Mas70p, yet are viable and able to respire. Protein import into mitochondria isolated from these cells is efficient, specific, and highly sensitive to protease treatment. We propose that at least one additional mitochondrial surface protein can function as a protein import receptor and that the activity of this component is up-regulated by a stress response or by an extragenic suppressor.

Protein import into mitochondria: the requirement for external ATP is precursor-specific whereas intramitochondrial ATP is universally needed for translocation into the matrix

ATP is needed for the import of precursor proteins into mitochondria. However, the role of ATP and its site of action have been unclear. We have now investigated the ATP requirements for protein import into the mitochondrial matrix. These experiments employed an in vitro system that allowed ATP levels to be manipulated both inside and outside the mitochondrial inner membrane. Our results indicate that there are two distinct ATP requirements for mitochondrial protein import. ATP in the matrix is always needed for complete import of precursor proteins into this compartment, even when the precursors are presented to mitochondria in an unfolded conformation. In contrast, the requirement for external ATP is precursor-specific; depletion of external ATP strongly inhibits import of some precursors but has little or no effect with other precursors. A requirement for external ATP can often be overcome by denaturing the precursor with urea. We suggest that external ATP promotes the release of precursors from cytosolic chaperones, whereas matrix ATP drives protein translocation across the inner membrane.

Import of cytochrome b2 to the mitochondrial intermembrane space: the tightly folded heme-binding domain makes import dependent upon matrix ATP

Cytochrome b2 is synthesized as a precursor in the cytoplasm and imported to the intermembrane space of yeast mitochondria. We show here that the precursor contains a tightly folded heme-binding domain and that translocation of this domain across the outer membrane requires ATP. Surprisingly, it is ATP in the mitochondrial matrix rather than external ATP that drives import of the heme-binding domain. When the folded structure of the heme-binding domain is disrupted by mutation or by urea denaturation, import and correct processing take place in ATP-depleted mitochondria. These results indicate that (1) cytochrome b2 reaches the intermembrane space without completely crossing the inner membrane, and (2) some precursors fold outside the mitochondria but remain translocation-competent, and import of these precursors in vitro does not require ATP-dependent cytosolic chaperone proteins.

Nitric oxide-dependent and -independent hyperaemia due to calcitonin gene-related peptide in the rat stomach

1. Calcitonin gene-related peptide (CGRP) potently enhances mucosal blood flow in the rat stomach. The aim of this study was to examine whether CGRP also dilates extramural arteries supplying the stomach and whether the vasodilator action of CGRP involves nitric oxide (NO). 2. Rat CGRP-alpha (0.03-1 nmol kg-1, i.v.) produced a dose-dependent increase in blood flow through the left gastric artery (LGA) as determined by an ultrasonic transit time technique in urethane-anaesthetized rats. Blockade of NO synthesis by NG-nitro-L-arginine methyl ester (L-NAME, 20 and 60 mumol kg-1, i.v.) significantly reduced basal blood flow (BF) in the LGA and attenuated the hyperaemic activity of CGRP by a factor of 2.8-4. D-NAME tended to enhance basal BF in the LGA but had no influence on the dilator activity of CGRP. The ability of vasoactive intestinal polypeptide to increase left gastric arterial blood flow remained unaltered by L-NAME. 3. L-NAME (20 and 60 mumol kg-1, i.v.) evoked a prompt and sustained rise of mean arterial blood pressure (MAP) and caused a slight decrease in the hypotensive activity of CGRP. In contrast, D-NAME induced a delayed and moderate increase in MAP and did not influence the hypotensive activity of CGRP. 4. Rat CGRP-alpha dilated the isolated perfused bed of the rat LGA precontracted with methoxamine and was 3 times more potent in this respect than rat CGRP-beta. The dilator action of rat CGRP-alpha in this preparation was not affected by L-NAME or D-NAME (40 microM). 5. L-NAME (60 micromol kg-1, i.v.) reduced gastric mucosal blood flow as assessed by laser Doppler flowmetry and diminished the hyperaemic activity of rat CGRP-alpha in the gastric mucosa by a factor of 4.5, whereas D-NAME was without effect.6. These data show that CGRP is a potent dilator of mucosal and extramural resistance vessels in the rat stomach. Its dilator action involves both NO-dependent and NO-independent mechanisms.

[Acute and long-term results of coronary Excimer laser angioplasty]

Laser and catheter technology have been considerably improved within the first 2 years of the clinical use of coronary excimer laser angioplasty. Furthermore, patient selection has changed due to increasing operator experience. We report on the acute- and long-term results achieved in 163 patients in three subgroups with different system parameters and catheter technology. In the initial series 1 (N:60) a prototype catheter with a diameter of 1.4 mm was used. In series 2 and 3, we employed improved transmission devices with 1.3, 1.5 or 1.8 mm. In series 3 the pulsewidth was increased from 60 ns to 115 ns. The target vessel was the LAD in 68%, the LCX in 10%, and the RCA in 21%. According to the AHA/ACC Lesion classification there were 13% type A, 26% type B1, 55% type B2, and 5% type C lesions. Stand-alone laser angioplasty was performed in 23/60 (38%), 24/40 (60%), and 34/64 (53%) in series 1, 2, and 3, respectively. Additional balloon angioplasty was necessary in 32, 11, and 21 interventions. Failure of laser angioplasty occurred in five patients of series 1 and 2, and nine patients of series 3. Frequently observed complications included coronary spasm in 18 to 32%, dissections in 16% to 33%, and vessel closure in 18 to 27%. Myocardial infarction occurred in three patients in the first and one patient of the second and third series. There was one in-hospital death in series 1 and 2.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of ATP in the intramitochondrial sorting of cytochrome c1 and the adenine nucleotide translocator

Import of precursor proteins across the mitochondrial inner membrane requires ATP in the matrix. However, some precursors can still cross the outer membrane in ATP-depleted mitochondria. Here we show that the adenine nucleotide translocator is imported normally into the inner membrane after the matrix has been depleted of ATP. This result supports the earlier suggestion that the translocator inserts into the inner membrane without passing through the matrix. Depletion of matrix ATP also has no detectable effect on the import and maturation of cytochrome c1, which is targeted to the intermembrane space. It thus seems probable that cytochrome c1 does not completely cross the inner membrane during its import pathway.

Putting energy into mitochondrial protein import

The import of proteins into mitochondria occurs in several steps. At least three of these steps require ATP and involve molecular chaperones. This energy requirement has served as a useful tool for elucidating the import pathways into the four mitochondrial compartments.

Protein import into the yeast mitochondrial matrix. A new translocation intermediate between the two mitochondrial membranes

Import of authentic or artificial precursor proteins into the matrix of isolated yeast mitochondria can proceed via a translocation intermediate that is lodged between the two mitochondrial membranes. The intermediate accumulates when import is arrested by depleting mitochondria of ATP. Generation of the intermediate requires a potential across the inner membrane. The intermediate is membrane-bound, partly or completely processed (depending on the precursor), and chased into the matrix by added ATP. This chase does not require a potential across the inner membrane. The properties of this intermediate support the proposal (Hwang, S., Jascur, J., Vestweber, D., Pon, L., and Schatz, G. (1989) J. Cell Biol. 109, 487-493) that import into the matrix involves two distinct translocation systems in the outer and the inner mitochondrial membrane that are not permanently coupled to each other. Only translocation across the inner membrane requires ATP in the matrix.

Protein import into mitochondria: two systems acting in tandem?

Mitochondria can import proteins from the cytoplasm at sites where the two mitochondrial membranes are closely apposed. However, each of these membranes contains a distinct protein translocation channel. Recent evidence suggests that the two types of channel are not permanently coupled, but may dissociate in a reversible manner. This reversible interaction is probably essential for intramitochondrial sorting proteins.

Erythrocyte deformability in patients on left ventricular assist systems

Preliminary hemorheologic studies using clinical filtration techniques on blood cell suspensions have suggested that changes in erythrocyte (RBC) deformability occur during left ventricular assist system (LVAS) support. In the biophysics literature, it is generally accepted that the elastic properties of the RBC membrane complex affect the microcirculatory deformability of the whole cell (cytoplasmic pathologies excepted). This paper compares single cell measurements of the surface shear elastic modulus, mu, of the RBC membrane complex (determined using micropipette aspiration) to available clinical filtration pressure data during Novacor LVAS support, over 33 and 126 days in four patients.

Propagation phenomena of nonlinear film guided waves in a configuration with material losses: a numerical analysis

The propagation of TE-polarized nonlinear guided waves excited at different points of the nonlinear dispersion curve has been examined along a thin film bounded by two identical self-focusing media with linear absorption. The evolution of the fields indicates that the stable branches of the nonlinear dispersion curve can be passed through when the total energy flow decreases because of absorption. The evolution of nonstationary waves initially excited at unstable branches of the dispersion curve shows significant dependence on the magnitude of the absorption.

Propagation phenomena of nonlinear film-guided waves: a numerical analysis

The propagation of TE guided waves excited at different points of their dispersion curve has been numerically traced down a thin film bounded by two identical self-focusing media. Several types of nonstationary field evolution have been investigated and identified as transitions between or oscillations around different branches of the dispersion curve.

Isolation of a cAMP receptor protein from yeast mitochondria (Mr 45000) and comparison with mitochondrial RNA polymerase (Mr 45000)

We have isolated a cAMP-binding protein from highly purified yeast mitochondria by affinity chromatography. It is a lipophilic protein of molecular mass 45 000 Da, which is tightly membrane-bound and localized on the outer surface of the inner membrane. It can be solubilized in active form under mild conditions. The cAMP receptor resembles mitochondrial RNA polymerase prepared as described by Levens et al. [(1981) J. Biol. Chem. 256, 1474] in a surprisingly large number of properties including molecular mass. Comparison of the two proteins revealed that the polypeptide previously considered as RNA polymerase is, in fact, a mitochondrial cAMP receptor protein.

Experiences using chloramine-T and 1, 3, 4, 6-tetrachloro-3 alpha, 6 alpha-diphenylglycoluril (Iodogen) for radioiodination of materials for radioimmunoassay

A comparison of labelling compounds with chloramine-T and with 1, 3, 4, 6-tetrachloro-3 alpha, 6 alpha-diphenylglycoluril (Iodogen) has been carried out. For human transferrin, human calcitonin, 1-84 bovine parathyrin, fibrinopeptide-A, human thyrotropin and F-CB3, a cyanogen bromide cleavage peptide of human fibrinogen, the quality of tracer produced by the Iodogen method was better. For rat lutropin, human growth hormone and human prolactin, labelling with Iodogen produced a tracer of unsatisfactory quality. For a further 13 peptides, the results from both methods were comparable. Optimal reaction times using Iodogen were of the magnitude of two to three times longer than when using chloramine-T. Reduction of the volume of radioactive waste by up to 90% could be achieved when the Iodogen method was coupled with a short cation-exchange column to separate unreacted iodide from the labelled compound. Data is presented on the quality of tracer, expressed in terms of elution profiles and radioimmunoassay standard curves. A novel "combi-method" of labelling proteins without tyrosine or histidine moieties is presented where N-succinimidyl-3-(4-hydroxyphenyl)-propionate is labelled at pH 7.5 using Iodogen to give "Bolton-Hunter" reagent, which is then transferred to a vessel containing the peptide to be labelled at ph 8.6.

Preliminary results on the use of an antiserum to human parathyrin in a homologous radioimmunoassay

A new antiserum (Ab Giselle) raised in sheep against extracted human parathyrin was evaluated and compared with an established antiserum (Ab S-478 VI) under several test conditions. The assay system contained an extracted 1--84 human parathyrin standard and a 1--84 bovine parathyrin tracer. The total assay time was 24 h and the main assay characteristics as follows: B0/T 0.28 +/- 0.02 and 50% intercept 553 +/- 47 U . 1(-1). The corresponding data for Ab S-478 VI were: B0/T 0.23 +/- 0.02 and 50% intercept 890 +/- 142 U . 1(-1). The normal range in 152 normocalcaemic volunteers (age range 16--67 years) was 10.6--423 U . 1(-1) (where 1 vial MRC reference preparation 75/549 for human parathyrin = 25 U), compared with 0--300 U . 1(-1) for Ab S-478 VI. With the new antiserum, differentiation between hypoparathyroid patients and those with normal function was often possible, and differentiation between normal and elevated levels, as in hyperparathyrinaemia, was very good. Correlation between Ab Giselle and Ab S-478 VI in 80 normal volunteers was positive (r = 0.450, p = 0.01) although the regression line showed that the antisera had different specificities (data for the regression line y = a + bx, a = 0.13, b = 0.55). Under the assay conditions, the association constant for Ab Giselle was 0.41 +/- 10(14) l . mol-1 in contrast to Ab S-478 VI which had a Ka for 0.53 x 10(10) l . mol-1 under identical conditions. Assays using Ab Giselle could be performed at room temperature, whereas those using Ab S-478 VI performed best at 0 degrees C. Preliminary results suggest that Ab Giselle is better for the routine assay of human parathyrin in serum than Ab S-478 VI, especially in the case of hypoparathyroid patients.

A critical appraisal of a further three new commercial digoxin radioimmunoassay kits with reference to cross-reacting substances

A further 3 digoxin radioimmunoassay (RIA) kits have been evaluated for performance and cross-reaction with digitoxin, spironolactone, canrenone and furosemide (Lasix-Hoechst). Effects of serum protein concentrations have also been tested. The kits tested were from the following manufacturers: A) Diagnostic Products Corporation Digoxin RIA Kit. B) Byk-Mallinckrodt SPAC Digoxin Kit. C) Boehringer-Mannheim Digoxin RIA Kit. All kits used a 125I-labelled tracer. Kit A used a conventional liquid phase system using double-antibody separation for bound and free drug, Kits B and C used a solid-phase antibody coated tube method. All kits showed a lower cross-reaction to digitoxin than quoted by the manufacturer. Cross-reaction to spironolactone (Aldactone--Boehringer-Mannheim) was less than 1.50 nmol/l at a serum concentration of 125 mg/l Aldactone in all 3 kits. The cross-reaction to canrenone was somewhat higher, 5.2 nmol/l "digoxin" being measured in one kit at a serum canrenone concentration of 125 mg/l. There was no cross-reaction with furosemide in any kit, even at a serum concentration of 5 g/l. The coated-tube assays were affected by serum albumin and globulin concentration changes, one kit showing a difference of over 50% binding in the range 1--20% albumin. The double-antibody kit did not show dependence on the concentration of these proteins. All kits measured digoxin with good reproducibility in the range 0.40--10.0 nmol/l.