Long lasting anti-adrenergic effect of 7-oxo-prostacyclin in the heart: a cycloheximide sensitive increase of phosphodiesterase isoform I and IV activities

Evidence is accumulating that 7-oxo-prostacyclin (7-oxo-PGI₂) induces a delayed indirect anti-adrenergic and cytoprotective effect on the myocardium, the mechanism of which is still unclear. To demonstrate that a single application of 7-oxo-PGI₂ (50 g/kg i.m.) 48 h prior to starting experiments attenuates the isoprenaline inducible inotropic response and accumulation of cAMP, isolated hearts of pretreated animals were perfused in the Langendorff mode with and without isoprenaline (1 to 100 nM). The late anti-adrenergic effect of the drug was manifested by a significant attenuation in the elevation of cAMP levels as well as in contractile force development. This effect was not due to changes in cAMP generation as there were identical ₁-adrenoceptor densities and affinities (as calculated from [³H]-CGP binding studies), G_i and G_s protein patterns (as taken from Western blots) as well as adenylyl cyclase activity measurements in the hearts studied. The anti-adrenergic potency of 7-oxo-PGI₂, however, was found to be related to a significant rise in cyclic nucleotide hydrolysis by phosphodiesterase (PDE). Using the fast-performance liquid chromatographic separation for PDE isoforms, a significant increase in the activity of PDE isoforms I and IV (260±28 vs 110±12 pmol cGMP/min x enzyme fraction and 77±11 vs 34±3 pmol cAMP/min x enzyme fraction, respectively) was found in the solubilized fraction of cardiac membranes in comparison to untreated controls; PDE IV activity was also increased in the cytosolic fraction (106±14 vs 65±6 pmol cAMP/min x enzyme fraction). The hypothesis that the delayed anti-adrenergic effect of 7-oxo-PGI₂ is initiated by an induction and accelerated synthesis of PDE I and IV in the heart is underlined by the fact that cycloheximide suppresses completely both the rise in PDE activities and the anti-adrenergic effects studied. It is suggested that an inducible predominance of cAMP degradation over its generation may be of relevance in processes related to heart protection.     

The influence of the cytosolic oncotic pressure on the permeability of the mitochondrial outer membrane for ADP: implications for the kinetic properties of mitochondrial creatine kinase and for ADP channelling into the intermembrane space

Summary Cytosolic proteins as components of the physiological mitochondrial environment were substituted by dextrans added to media normally used for incubation of isolated mitochondria. Under these conditions the volume of the intermembrane space decreases and the contact sites between the both mitochondrial membranes increase drastically. These morphological changes are accompanied by a reduced permeability of the mitochondrial outer compartment for adenine nucleotides as it was shown by extensive kinetic studies of mitochondrial enzymes (oxidative phosphorylation, mi-creatine kinase, mi-adenylate kinase). The decreased permeability of the mitochondrial outer membrane causes increased rate dependent concentration gradients in the micromolar range for adenine nucleotides between the intermembrane space and the extramitochondrial space. Although all metabolites crossing the outer membrane exhibit the same concentration gradients, considerable compartmentations are detectable for ADP only due to its low extramitochondrial concentration. The consequences of ADP-compartmentation in the mitochondrial intermembrane space for ADP-channelling into the mitochondria are discussed.     

A novel human type I hair keratin gene: evidence for two keratin hHa3 isoforms

We present the nucleotide and amino acid sequence for a novel human type I hair keratin, which could be identified through its high sequence homology and strict carboxyterminal length identity as a human ortholog of the murine hair keratin mHa3. Our hHa3 sequence differs, however, from that of a previously described hHa3 hair keratin (published only as an amino acid sequence; [13]) in 24 amino acid positions, 8 of which occur in the middle of the carboxyterminal domain. PCR of genomic DNA from 25 normal human subjects using a primer pair derived from sequence segments located in the 3-region of our hHa3 clone that encode conserved amino acid sequences in both keratins, resulted in the amplification of two distinct products of 0.38 kbp and 1.0 kbp. DNA sequence analysis of the cloned PCR products allowed identification of the 0.38 kb sequence as that originating from Yuet al. [13] and the 1.0 kb sequence as that being derived from our data. The difference in fragment length was due to unique intron 6 sequences, indicating that these two keratin species are encoded by genes of their own. Moreover, extensive Southern blot analyses with DNA from 25 unrelated individuals of different races using a 3-noncoding sequence from our keratin and the intron 6 sequence of the keratin of Yuet al. [13], as hybridization probes showed that both keratin genes are present as single copy sequences occurring ubiquitously and without gross alterations in the human genome. Collectively, these data demonstrate that the human type I hair keratin described in this paper represents an isoform of the previously described hHa3 keratin. We propose that these hHa3 isoforms be named in chronological order of discovery hHa3-I and hHa3-II.     

Octopamine-like immunoreactive neurones in locust genital abdominal ganglia

Using a well characterized anti-serum, the distribution of octopamine-like immunoreactive neurones is described in the locust seventh abdominal (A7) and terminal ganglia (TG), which are associated with genital organs. Apart from 4 paired ventral somata occasionally observed in the TG, all labelled cells could be identified as efferent dorsal- and ventral unpaired median (DUM/VUM) neurones by virtue of the characteristic large size and position of their somata, projections of their primary neurites in DUM-cell tracts, and bifurcating axons which arise from dorsal T-junctions and enter peripheral nerves. For the examined ganglia our data indicate that the whole population of efferent DUM and VUM-cells, defined here as progeny of the segment specific unpaired median neuroblast with peripheral axons, are octopaminergic, and that equal numbers of these cells occur in both sexes: 8 in A7 and 11 in TG. Sex-specific differences are probably restricted to the axonal projections of 5 octopamine-like immunoreactive DUM-somata in A7, and 5 in TG, which in females project into their segment specific sternal nerves, but in males into the genital nerve of the TG. Numerous intersegmentally projecting octopamine-like immunoreactive fibres traverse both ganglia. The majority probably stem from previously described octopamine-like immunoreactive neurones in the thoracic and suboesophageal ganglia.     

Astrocytes alter their polarity in organotypic slice cultures of rat visual cortex

The ultrastructure of astrocytes in an organotypic slice culture of the rat visual cortex was investigated using ultrathin sections and freeze-fracture replicas. After a culture period of 9–15 days, a glial scaffold formed that separated the bulk of the slice neuropil from the medium and the underlying plasma clot. However, the glial cells and processes did not build a dense barrier but allowed the outgrowth of neurites. A basal lamina covering the medium-oriented surface of the astrocytes was not found. In freeze-fracture replicas, orthogonal arrays of particles (OAP) were characteristic components of astrocytic membranes. The OAP density in membranes bordering the medium was 35±13 OAP/m², corresponding to 2.5% of this membrane area; the OAP density in membranes within the slice neuropil was 22±12 OAP/², corresponding to 1.4% of this membrane area. Although the difference was significant, it was greatly reduced when comparing OAP densities in endfoot and non-endfoot membranes in vivo. Another mode of polarity was recognized in astrocytes of the organotypic slice culture. In membranes of astrocytes bordering upon the medium, the density of non-OAP intramembranous particles (IMP) was clearly higher (1130±136 IMP/ m²) than in membranes of astrocytes in the center of the slice (700±172 IMP/m²). This pronounced IMP-related polarity was observed neither in vivo nor in cultured astrocytes. The present study suggests, together with data from the literature, that the distribution of astrocytic OAP across the cell surface is influenced by the existence of a basal lamina and neuronal activity, and that astrocytes possess a more remarkable plasticity of membrane structure than previously suspected.     

Chorionic gonadotropin-like proteins in the obplacental giant cells of the rabbit

Diabetes mellitus was induced in 40 male C57BL6 mice by injection of a low dose of streptozocin (45 mg/kg body weight) on 5 consecutive days. Twenty four of the mice were immunosuppressed by administration of 1.5 mg FK506/kg body weight daily for 10, 15, 18 and 24 days. Administration of FK506 almost completely inhibited the streptozocin-induced islet damage, and consequently glycaemia remained normal. In FK506-treated animals any inflammatory infiltrate was very sparse and was limited to the vascular pole of the islets. Immunocytochemical results demonstrated that infiltrating cells were Ia-immunoreactive, but were not activated. Ultrastructural observations confirmed the absence of B cell necrosis and degranulation in FK506-treated mice; the few infiltrating elements encountered did not contain phagocytic vesicles or show other signs of activation.     

A novel, “hidden” penicillin-induced death of staphylococci at high drug concentration,occurring earlier than murosome-mediated killing processes

In log-phase cells of staphylococci, cultivated under high, non-lytic concentrations of penicillin G, there occurred a novel killing process hitherto hidden behind seemingly bacteriostatic effects. Two events are essential for the apprearance of this hidden death: (i) the failure of the dividing cell to deposit enough fibrillar cross-wall material to be welded together, and (ii) a premature ripping up of incomplete cross walls along their splitting system. Hidden death started as early as 10–15 min after drug addition, already during the first division cycle. It was the consequence of a loss of cytoplasmic constituents which erupted through peripheral slit-like openings in the incomplete cross walls. The loss resulted either in more or less empty cells or in cell shrinkage. These destructions could be prevented by raising the external osmotic pressure. In contrast, the conventional non-hidden death occurred only much later and exclusively during the second division cycle and mainly in those dividing cells, whose nascent cross walls of the first division plane had been welded together. These welding processes at nascent cross walls, resulting in tough connecting bridges between presumptive individual cells, were considered as a morphogenetic tool which protects the cells, so that they can resist the otherwise fatal penicillin-induced damages for at least an additional generation time (morphogenetic resistance system). Such welded cells, in the virtual absence of underlying cross-wall material, lost cytoplasm and were killed via ejection through pore-like wall openings or via explosions in the second division plane and after liberation of their murosomes, as it was the case in the presence of low, lytic concentrations of penicillin. Bacteriolysis did not cause any of the hitherto known penicillin-induced killing processes.Dedicated to Prof. Dr. Georg Henneberg on the occasion of his 85th birthday