Plasma protein haptoglobin modulates renal iron loading

Haptoglobin is the plasma protein with the highest binding affinity for hemoglobin. The strength of hemoglobin binding and the existence of a specific receptor for the haptoglobin-hemoglobin complex in the monocyte/macrophage system clearly suggest that haptoglobin may have a crucial role in heme-iron recovery. We used haptoglobin-null mice to evaluate the impact of haptoglobin gene inactivation on iron metabolism. Haptoglobin deficiency led to increased deposition of hemoglobin in proximal tubules of the kidney instead of the liver and the spleen as occurred in wild-type mice. This difference in organ distribution of hemoglobin in haptoglobin-deficient mice resulted in abnormal iron deposits in proximal tubules during aging. Moreover, iron also accumulated in proximal tubules after renal ischemia-reperfusion injury or after an acute plasma heme-protein overload caused by muscle injury, without affecting morphological and functional parameters of renal damage. These data demonstrate that haptoglobin crucially prevents glomerular filtration of hemoglobin and, consequently, renal iron loading during aging and following acute plasma heme-protein overload.     

Regulation and possible physiological role of the Ca2-dependent K+ channel of cortical collecting ducts of the rat

In the luminal membrane of rat cortical collecting duct (CCD) a big Ca²⁺-dependent and a small Ca²⁺-independent K⁺ channel have been described. Whereas the latter most likely is responsible for the K⁺ secretion in this nephron segment, the function of the large-conductance K⁺ channel is unknown. The regulation of this channel and its possible physiological role were examined with the conventional cell-free and the cell-attached nystatin patch-clamp techniques. Patch-clamp recordings were obtained from the luminal membrane of isolated perfused CCD segments and from freshly isolated CCD cells. Intracellular calcium was measured using the calcium-sensitive dye fura-2. The large-conductance K⁺ channel was strongly voltage- and calcium-dependent. At 3 mol/l cytosolic Ca²⁺ activity it was half-maximally activated. At 1 mmol/l it was neither regulated by cytosolic pH nor by ATP. At 1 mol/l Ca²⁺ activity the open probability (P _o) of this channel was pH-dependent. At pH 7.0 P _o was decreased to 4±2% (n=9) and at pH 8.5 it was increased to 425±52% (n=9) of the control. At this low Ca²⁺ activity the P _o of the channel was reduced by 1 mmol/l ATP to 8±4% (n=6). Cell swelling activated the large-conductance K⁺ channel (n=14) and hyperpolarized the membrane potential of the cells by 9±1 mV (n=23). Intracellular Ca²⁺ activity increased after hypotonic stress. This increase depended on the extracellular Ca²⁺ activity. A possible physiological function of the large-conductance K⁺ channel in rat CCD cells may be the reduction of the intracellular K⁺ concentration after cell swelling. Once this channel is activated by increases in the cytosolic Ca²⁺ activity it can be regulated by changes in cellular pH and ATP.Supported by DFG Schl 277/2-3     

Die Veränderung der corticalen Gleichspannung bei kompletter und inkompletter Ischämie des Gehirns

Zusammenfassung Die corticale Gleichspannung wurde an isolierten Hundeköpfen von der Konvexität des Gehirns (Gyrus lateralis) gegen Nase (Knochenoberfläche des os frontale) bei kompletter und inkompletter Gehirnischämie gemessen.Während kompletter Gehirnischämie verschiebt sich die Gleichspannung nach einer initialen Positivierung, die 1,5–2,75 min nach Ischämiebeginn ein Maximum von 1,5–2 mV erreicht, in negativer Richtung. Diese Negativierung erreicht 3–8 min nach Ischämiebeginn einen steady state von im Mittel 6,5 mV. Nach Ende der kompletten Gehirnischämie kommt es nach einer kurzfristigen Positivierung zu einer länger dauernden Negativierung.Bei inkompletter Gehirnischämie kommt es zu einer Negativierung der Gleichspannung, wenn der Blutdruck auf 80–40 mm Hg abgefallen ist. Es wird vermutet, daß die Negativierung bei der für das Gehirn kritischen Blutdruckhöhe beginnt.Auszugsweise vorgetragen auf der 31. Tagung der Deutschen Physiologischen Gesellschaft Würzburg 1966 [Pflügers Arch. ges. Physiol. 289, R 5 (1966)].     

Dorsal tegmentum kindling in rats.

Electrical stimulations were applied daily for 40 days to the dorsal tegmentum in 9 rats through chronically implanted bipolar electrodes. The intensity of current (2 s trains of 50 Hz, 1 ms monophasic square waves) necessary to trigger a full tonic seizure was determined and applied for all further stimulations. Initial stimulations induced a tonic seizure with a low voltage fast electrocorticographic activity. After repeated stimulations, high amplitude spike and wave discharges developed over the cortex, their duration exceeding 50 s at the 40th stimulation. Simultaneously, the tonic seizures evolved into tonic-clonic fits with bilateral myoclonias following the tonic phase. These EEG and behavioral modifications persisted for 30 days after the last stimulus. These results demonstrate that kindling may be obtained from brainstem structures.     

A recombinant vaccinia virus expressing hepatitis B virus middle surface protein Restricted expression of HBV antigens in human diploid cells

Summary Several vaccinia virus recombinants inducing the synthesis of the middle surface (M) protein of hepatitis B virus (HBV) were constructed. One of them, denoted vl37, was examined in some detail. The virus replicated nearly to the same extent in various cell lines, viz. human embryo diploid fibroblast LEP and MRC-5 cells, rabbit embryo fibroblast REF cells, TK^– rat RAT-2 cells, and green monkey CV-1 cells. However, the production of M protein was found considerably lower in the human LEP and MRC-5 than in the other cells examined. In addition, the kinetics of M formation were different in these two cell systems, LEP cells lagging significantly behind CV-1 cells. The low-level production of M protein in LEP cells was not increased by repeated vl37 passages in LEP cells, nor by a passage in a laboratory worker accidentally infected with the vl37 virus, nor by shortening the leader sequence preceding the translation initiation codon. The greater part of the M antigen was found to be cell associated, more so in the cells of human than monkey origin. From the major HBV S antigen (HBsAg) isolated from the plasma of chronically infected subjects, the antigen released by cell destruction differed by binding to polymerized human albumin. This property was utilized in ELISA to detect anti-preS2 antibody. Rabbits inoculated intradermally with the vl37 virus developed antibodies reactive in this assay as well as with a synthetic peptide corresponding in the amino acids 14–34 of the NH₂terminus of the HBsAg preS2 region.     

Effects of diadenosine polyphosphates,ATP and angiotensin II on membrane voltage and membrane conductances of rat mesangial cells

Diadenosine polyphosphates have been shown to influence renal perfusion pressure. As mesangial cells may contribute to these effects we investigated the effects of diadenosine triphosphate (Ap₃A), diadenosine tetraphosphate (Ap₄A), diadenosine pentaphosphate (Ap₅A) and diadenosine hexaphosphate (Ap₆A) on membrane voltage (V _m) and membrane conductance (g _m) in mesangial cells (MC) of normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats in primary and long-term culture. We applied the patch-clamp technique in the fast-whole-cell configuration to measure V _m and g _m. To compare the effects of diadenosine polyphosphates with hitherto known agonists we also tested adenosine 5-triphosphate (ATP) and angiotensin II (Ang II). As there was no significant difference in the V _m values in MC of WKY (–42±1 mV, n=70) and SHR rats (–45±2 mV, n=99) as well as in the agonist-induced changes of V _m, all data were pooled. The V _m of all the cells was –44±1 mV (n=169) and g _m was 15.9±1.8 nS (n=141). Ion-exchange experiments showed the presence of a K⁺ and a non-selective cation conductance in resting MC whereas a Cl^– conductance or a Na⁺selective conductance could not be observed. Ap₃A, Ap₄A, Ap₅A, AP₆A and ATP each at a concentration of 5 mol/l, led to a significant depolarization of V _m by 5±2 mV (n=14), 7±1 mV (n=25), 3±1 mV (n=23), 2±1 mV (n=16), and 14±2 mV (n=23), respectively. For Ap₄A, the most potent diadenosine polyphosphate, we determined the half-maximally effective concentration (EC ₅₀) as 6 mol/l (n=5–25), for ATP as 2 mol/l (n=9–37), and for Ang II as 8 nmol/l (n=6–18). Ap₄A 100 mol/l increased g _m significantly by 55±20% (n=16), 100 mol/l ATP by 135±60% (n=18). The diadenosine polyphosphates examined were able to depolarize V _m (Ang II >ATP> Ap₄A>Ap₃A>Ap₅A>Ap₆A) by activation of a Cl^– conductance and a non-selective cation conductance, as do ATP or Ang II.     

Are the metabolic characteristics of congenital intraspinal lipoma cells identical to,or different from normal adipocytes?

Congenital intraspinal lipomas are frequently responsible for progressive neurological deficits caused by distortion or compression of the nervous system. Since fat metabolism in these lesions has not been previously studied, the aim of this study was to determine whether intraspinal lipoma cells behave like lipomas or like normal adipocytes. In 11 patients, intraspinal lipoma cells were compared with normal adipocytes isolated from adjacent subcutaneous adipose tissue for the following parameters: lipoprotein lipase (LPL), lipogenesis from U¹⁴C glucose, ß-receptor number, adenylate cyclase activity, cyclic AMP production, and lipolysis in response to ß- and ₂-adrenergic agonists. No significant difference between these two cell populations was found, suggesting that intraspinal lipomas are not lipomatous tumors, but hamartomatous lesions capable of growth and regression along with the changes in the rest of the fatty pool. This emphasizes the danger of an abnormal weight gain, as well as the possible usefulness of an hypocaloric diet in patients who worsen in spite of previous surgery.Research supported by INSERM (CRL 824005 and CRE 854010) and the D.G.R.     

Association of antiviral prophylaxis and rituximab use with posttransplant lymphoproliferative disorders (PTLDs): A nationwide cohort study

Posttransplant lymphoproliferative disorder (PTLD) is a serious complication of solid organ transplantation (SOT). Most PTLD cases are associated with Epstein–Barr virus (EBV) infection. The role of antiviral prophylaxis or rituximab therapy for prevention of PTLD in SOT recipients is controversial. In a nationwide cohort, we assessed the incidence, presentation, and outcome of histologically proven PTLD. We included 4765 patients with a follow-up duration of 23 807 person-years (py). Fifty-seven PTLD cases were identified; 39 (68%) were EBV positive (EBV+ PTLD). Incidence rates for EBV+ PTLD at 1, 2, and 3 years posttransplant were 3.51, 2.24, and 1.75/1000 py and 0.44, 0.25, and 0.29/1000 py for EBV− PTLD. We did not find an effect of antiviral prophylaxis on early and late EBV+ PTLD occurrence (early EBV+ PTLD: SHR 0.535 [95% CI 0.199–1.436], p = .264; late EBV+ PTLD: SHR 2.213, [95% CI 0.751–6.521], p = .150). However, none of the patients (0/191) who received a rituximab-containing induction treatment experienced PTLD, but 57 of 4574 patients without rituximab induction developed PTLD. In an adjusted restricted mean survival time model, PTLD-free survival was significantly longer (0.104 years [95% CI 0.077–0.131]) in patients receiving rituximab as induction treatment. This study provides novel data on the association of rituximab induction and reduced risk for PTLD.