S-100 + lymph node neoplasm

Summary A 16-yr-old white female was affected by continuous fever, pancytopenia with relative increase of T-8 lymphocytes, severe bone marrow hypoplasia, generalized lymphadenomegaly and splenomegaly. A first lymph node biopsy, obtained at the onset of the disease, was involved by a paracortical tumor with some S-100+ lymphocyte-like cells in the neoplastic areas; in the cell suspension, 70–80% of cells were E4 + /E37 + lymphocytes with prevalent expression of the T-8 phenotype (52%). A second lymph node biopsy, obtained five months later, was involved by a diffuse proliferation of S-100 + cells with high mitotic activity; in the cell suspension, the majority of cells were E-/T-11+/ T-3+/T-8+. At the TEM level, the neoplastic cells were characterized by regular or indented nuclei with finely dispersed chromatin and by regular or indented nuclei with finely dispersed chromatin and by irregular cytoplasmic profiles with thick pseudopodia-like projections. The possibility is discussed that this neoplasm may share some similarities with the T- lymphoma being part of a poorly described group of tumors with intermediate features between T cell lymphoma and malignant histiocytosis.Supported by CNR contract N. 83.00724.96, Progetto Finalizzato Controllo della crescita neoplastica     

Studies of human natural killer cells. III. Neutropenia associated with unusual characteristics of antibody-dependent and natural killer cell-mediated cytotoxicity

A 52-year-old Caucasian man with chronic neutropenia and recurrent infections was found to have an increased proportion of peripheral T lymphocytes having Fc receptors for IgG (T(). Although levels of antibody-dependent cell-mediated cytotoxicity (ADCC) and natural killing (NK) by unfractionated lymphocytes were similar to those of a control donor, the frequency of NK cells was markedly increased. Removal of E rosette-forming cells eliminated both NK and ADCC by the patient's peripheral blood, in marked contrast to theenhanced cytotoxicity seen with control lymphocytes. Both normal and patient ADCC and NK functions were removed by depletion of Fc receptor-bearing cells. These depletion experiments proved that all of the patient's killer cells were E rosetteforming T cells, in contrast to the heterogeneous pattern of Null and T killer cells seen in the blood of normal donors. The homogeneity of the T proliferation suggested that ADCC and NK were mediated by the same cell type, albeit acting by different mechanisms. The addition of the patient's serum and lymphocytes to chromiumlabeled normal granulocytes caused a low but significant level of cytotoxicity, indicating that the patient's neutropenia may have been caused by a similar mechanismin vivo. There was no evidence of complement-dependent serum antibody-mediated neutrophil lysis, but one serum sample taken over the course of the patient's disease agglutinated granulocytes from four of five donors tested.     

Das Membranverhalten der interepithelialen Lymphocyten des Darmes

Summary The membrane behaviour of interepithelial lymphocytes and epithelium cells of the digestive tract was investigated by electron microscopy with the aid of ruthenium red staining. Biopsy specimens of nonspecific proctitis, ulcerative colitis, Crohn's disease, Whipple's disease, chronic lymphadenosis with gastrointestinal involvement and various intestinal polyps and carcinomae were examined. The ruthenium red dye was prepared largely according to the method described by Luft (1971 a). Ruthenium red stains the perilymphocytic areas in two different forms: First: the apical perilymphocytic area is usually characterized by homogeneous ruthenium red staining. The lateral boundaries of the epithelial cells above the lymphocytes are strikingly folded. Second: ruthenium red is deposited in the basal perilymphocytic area, predominantly in coarse granules. Epithelium-associated lymphocytes apparently cause local modifications to the character of the interstitium of the lamina epithelialis mucosae. The different affinity of the cell membranes of the lymphocytes for ruthenium red may indicate so-called distortion alterations of the cell membranes.

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Mit Unterstützung der Deutschen Forschungsgemeinschaft.     

12-deoxyphorbol-13-O-phenylacetate 20 acetate [an agonist of protein kinase Cβ1 (PKCβ1)] induces DNA synthesis,interleukin-2 (IL-2) production,IL-2 receptor α-chain (CD25) and β-chain (CD122) expression,and translocation of PKCβ isozyme in human peripheral blood lymphocytes: Evidence for a role of PKCβ1 in human T cell activation

To determine a role of protein kinase C (PKC) isozymes in lymphocyte activation, human peripheral blood mononuclear cells were activated with 12-deoxyphorbol-13-O-phenylacetate (dPP; an agonist of both calcium-dependent and calcium-independent PKC isozymes), thymeleatoxin (TX; an activator of calcium-dependent PKC, , and ), and 12-deoxyphorbol-13-O-phenylacetate 20 acetate (dPPA; an activator of PKC1 isozyme) and examined for DNA synthesis, lymphocyte proliferation, interleukin-2 (IL-2) production, expression of IL-2 receptor and chains on CD3+, CD4+, and CD8+ T lymphocytes and CD20+ B lymphocytes, and translocation of PKC isozyme from cytosol to membrane fraction. The results show that dPPA activates lymphocytes by inducing the above changes in a manner analogous to that of dPP, TX, and phorbol myristate acetate. These data suggest that PKC1 is involved in the activation of human peripheral blood T and B lymphocytes.     

Interaction of transforming growth factor β1 with human glomerular epithelial cells in culture: opposite effects on synthesis of matrix proteins and on urokinase plasminogen activator

The effect of transforming growth factor- (TGF-) was analyzed on the synthesis of fibronectin, collagen type IV, and urokinase plasminogen activator in human glomerular epithelial cells in culture. An increase in the abundance of specific mRNA was found for collagen type IV and fibronectin. Fibronectin protein synthesis was also increased in TGF- treated cells; most of the de novo synthesized fibronectin was found as an unsoluble protein associated with extracellular matrix. In the same cells the amount of plasminogen activator mRNA was found leading also to a decreased surface expression of urokinase plasminogen activator. The data support the concept that by upregulating matrix protein synthesis and downregulating the plasminogen activator system, TGF- favors the development of sclerosis.Abbreviations FN Fibronectin - GEC Glomerular epithelial cells - TGF- Transforming growth factor - uPA Urokinase-type plasminogen activator     

Heterogeneity of myofibroblast phenotypic features: an example of fibroblastic cell plasticity

Granulation tissue fibroblasts (myofibroblasts) develop several ultrastructural and biochemical features of smooth muscle (SM) cells, including the presence of microfilament bundles and the expression of -SM actin, the actin isoform present in SM cells and myoepithelial cells and particularly abundant in vascular SM cells. Myofibroblasts have been suggested to play a role in wound contraction and in retractile phenomena observed during fibrotic diseases. When contraction stops and the wound is fully epithelialized, myofibroblasts containing -SM actin disappear, probably as a result of apoptosis, and the scar classically becomes less cellular and composed of typical fibroblasts with well-developed rough endoplasmic reticulum but with no more microfilaments. In contrast, -SM actin expressing myofibroblasts persist in hypertrophic scars and in fibrotic lesions of many organs, including stroma reaction to epithelial tumours, where they are allegedly involved in retractile phenomena as well as in extracellular matrix accumulation. The mechanisms leading to the development of myofibroblastic features remain to be investigated. In vivo and in vitro investigations have shown that -interferon exerts an antifibrotic activity at least in part by decreasing -SM actin expression whereas heparin increases the proportion of -SM actin positive cells. Recently, we have observed that the subcutaneous administration of transforming growth factor-1 to rats results in the formation of a granulation tissue in which -SM actin expressing myofibroblasts are particularly abundant. Other cytokines and growth factors, such as platelet-derived growth factor, basic fibroblast growth factor and tumour necrosis factor-, despite their profibrotic activity, do not induce -SM actin in myofibroblasts. In conclusion, fibroblastic cells are relatively undifferentiated and can assume a particular phenotype according to the physiological needs and/or the microenvironmental stimuli. Further studies on fibroblast adaptation phenomena appear to be useful for the understanding of the mechanisms of development and regression of pathological processes such as wound healing and fibrocontractive diseases.     

Untersuchungen zur Ultrastruktur lympho-epithelialer Thymustumoren unter besonderer Berücksichtigung der sog. „Emperipolesis“

Summary The ultrastructure of eleven thymomas with lymphocytic predominance, one epitheloid cell thymoma and two normal human thymuses is described with special reference to Emperipolesis. All patients have had myasthenia gravis.The normal human thymus consists of three parts: outer cortex, inner cortex, and medulla. The outer cortex contains mainly lymphoblasts and Metcalf's macrophages within the so-called Clark-packet's. The inner cortex consists mainly lymphocytes and interdigitating reticulum cells, and the medulla of epithelial cells, lymphocytes and Hassall's corpuscles.In all cases of lympho-epithelial thymoma and in normal human thymuses there are enormous interdigitations between epithelial (tumor) cells, lymphocytes and macrophages. The epitheloid cell thymomas also show findings which suggest an epithelial cell interaction. We have not found intact lymphocytes inside the cytoplasm of normal and/or tumor epithelial cells, macrophages or interdigitating reticulum cells.The intracellular existence of intact lymphocytes has been termed Emperipolesis by Humble, Jayne, and Pulvertaft, meaning internal wandering. These investigations indicate that Emperipolesis is not an adequate term for cellular interaction in normal human thymuses and thymomas. A false impression of intraepithelial location of thymic lymphocytes is created by two-dimensional sections of complex thymic structure. These ultrastructural studies revealed damage to lymphocytes only in macrophages with lymphocytolysis within these cells and accumulation of numerous heterophagic vacuoles containing fragments of lymphocytic debris within them.

FrÄulein C. Schürmann danke ich für die gute technische Assistenz, Herrn Priv.-Doz. Dr. med. R. W. Ch. Janzen, Neurologische Klinik der UniversitÄt Hamburg, für die klinischen Daten der Myasthenie-Patienten     

On the regulation of the expressed L-type calcium channel by cAMP-dependent phosphorylation

The Ca²⁺ channel subunits _1C-a and _1C-b were stably expressed in Chinese hamster ovary (CHO) and human embryonic kidney (HEK) 293 cells. The peak Ba²⁺ current (I _Ba) of these cells was not affected significantly by internal dialysis with 0.1 mM cAMP-dependent protein kinase inhibitor peptide (mPKI), 25 M cAMP-dependent protein kinase catalytic subunit (PKA), or a combination of 25 M PKA and 1 M okadaic acid. The activity of the _1C-b channel subunit expressed stably in HEK 293 cells was depressed by 1 M H 89 and was not increased by superfusion with 5 M forskolin plus 20 M isobutylmethylxanthine (IBMX). The _1C-a·₂·₂/ complex was transiently expressed in HEK 293 cells; it was inhibited by internal dialysis of the cells with 1 M H 89, but was not affected by internal dialysis with mPKI, PKA or microcystin. Internal dialysis of cells expressing the _1C-a·₂·₂/ channel with 10 M PKA did not induce facilitation after a 150-ms prepulse to +50 mV. The Ca²⁺ current (I _Ca) of cardiac myocytes increased threefold during internal dialysis with 5 M PKA or 25 M microcystin and during external superfusion with 0.1 M isoproterenol or 5 M forskolin plus 50 M IBMX. These results indicate that the L-type Ca²⁺ channel expressed is not modulated by cAMP-dependent phosphorylation to the same extent as in native cardiac myocytes.     

Neutralization of Transforming Growth Factor β1 Augments Hepatitis C Virus-Specific Cytotoxic T Lymphocyte Induction in Vitro

In hepatitis C virus (HCV) infection, TGF-1 is upregulated in the liver and may be involved in the pathogenesis of chronic liver disease. TGF-1 is also produced by activated T cells and acts as a potent immunosuppressor. The aim of this study was to investigate the roles of TGF-1 in HCV-specific cytotoxic T lymphocyte (CTL) induction and enhance their killer activity by TGF-1 modulation. We generated anti-HCV CTL from peripheral blood mononuclear cells from HLA-A2 patients under stimulation with the HCV-core peptide having the HLA-A2.1 binding motif. The lytic activities of CTL or precursor frequency (CTLpf) generated with or without anti-TGF-p antibody were compared. To optimize the IL-2 dose for CTL induction, low (50 U/ml) and high (500 U/ml) doses were tested and the lytic activities were compared. TGF-1 amounts in the supernatants were assessed by enzyme-linked immunosorbent assay and by their growth inhibitory effect on mink lung epithelial cells. CTL activity was enhanced by anti-TGF- antibody in a dose-dependent manner but CTLpf did not significantly change. A high dose of IL-2 reduced the activity to 45% of that observed with a low dose, whereas TGF-1 increased as the dose of IL-2 increased. Exogenous IL-10 reversed the inhibitory effect of a high dose of IL-2 on the killing activity by reducing TGF-1 mRNA expression in T cells and its production. These results demonstrated that endogenous TGF-1 is an autocrine suppressor in CTL induction in vitro. Therefore, the blockade of endogenous TGF-1 could enhance the killing potential of anti-HCV CTL.     

Effect of recombinant human interferon γ against human cytomegalovirus

Summary Escherichia coli-derived human interferon- (rIFN-) inhibited the replication of human cytomegalovirus (HCMV) synergistically when combined with IFN-. The induction of HCMV DNA polymerase was inhibited in rIFN--treated cells. It is suggested that the induction of 2–5 A synthetase does not play an important role in the anti-HCMV actions of IFNs.With 2 Figures     

Effects of verapamil on excitation-contraction coupling in single crab muscle fibers

Summary The effects of verapamil and its optical isomers on the electrical and mechanical characteristics of single muscle fibers ofCallinectes danae were studied. Verapamil (10–20 g/ml) blocked the procaine-and TEA-induced spikes; the blockade was preceded by reduction in the rate of rise of the up-stroke and increase in the duration of the action potentials. Inhibition of Ba-spikes required higher concentrations of verapamil (>50 g/ml). These concentrations reduced the amplitude of the normally occurring graded electrogenic membrane responses and reduced the rate of development of the current-induced tensions. With lower concentrations (10–30 g/ml) verapamil enhanced the negative afterpotentials and the peak amplitude of the local contractions elicited by depolarizing current pulses, while the graded membrane responses were not markedly modified. Verapamil (1–100 g/ml) did not affect the resting membrane potential but increased the effective membrane resistance. Determination of the cable characteristics by DC pulses indicated that verapamil (1–10 g/ml) shortens the membrane length constant, increases the specific resistivity of the sarcoplasm and, in most cases, increases the membrane time constant. Verapamil (10 g/ml) induced tension in these crab fibers. The contractions were potentiated in Na-deficient media, by increase in [Ca]₀, and by membrane depolarization; Ca-free salines depressed, and procaine abolished these contractions. The results suggest that verapamil affects both Ca and K conductances and interferes with the Ca-sequestering mechanisms of these fibers. The (–)-isomer of verapamil was more effective than the (+)-isomer with respect to tension development, prolongation and subsequent blockade of procainespikes and enhancement of current-induced after-potentials and contractions.This work was supported in part with grants from CNP_q (TC-16.897) and from CEPG-UFRJ     

Development of calretinin-immunoreactive unipolar brush-like cells and an afferent pathway to the embryonic and early postnatal mouse cerebellum

In the developing mouse hindbrain, immunoreactivity for calretinin, a calcium-binding protein, was first observed at embryonic day 10, and was localized to neuronal cell bodies in the reticular formation. By embryonic day 12, fibers emanated rostrally from the calretinin-immunoreactive neurons, extended dorsally and then caudally in the uncinate fasciculus to reach the developing cerebellar plate. These fibers crossed the cerebellar midline and were distributed to the contralateral side of the cerebellum. The number and intensity of staining of cell bodies in the reticular formation was reduced in postnatal mice. After postnatal day 1, it was no longer possible to discern the calretinin-immunoreactive fiber bundle in the brainstem, although fibers were still visible at the level of the uncinate fasciculus and in the cerebellum. We also observed intensely calretinin-immunoreactive, smaller cells in the cerebellum (embryonic day 14) and dorsal cochlear nuclei (embryonic day 18), most of which we believe are destined to become the unipolar brush, (also known as pale or monodendritic) cells observed in the adult mammalian brain. An immature form of these cells exists in the developing mouse cerebellum. Thus, using calretinin antiserum as a marker, an afferent neuronal system was described which projects to the cerebellar primordium. It is suggested that the calretinin-containing hook bundle is an afferent projection which provides a feed-forward neuronal system to the cerebellum which, in turn, projects afferent fibers to the calretinin-containing and other cells of the reticular formation.     

S-100 protein-positive Langerhans cells in various human lung cancers,especially in peripheral adenocarcinomas

Summary The appearance of S-100 protein-positive Langerhans cells was studied in 90 cases of various lung cancers by an immunohistochemical method. S-100 protein-positive dendritic cells were frequently observed in many adenocarcinomas, especially in those subclassified as bronchiolar cell or type II alveolar cell type. However, no S-100 protein-positive cells were found in goblet cell type adenocarcinoma. In some cases of squamous cell carcinoma and large cell carcinoma, these dendritic cells were also observed though they were fewer in number. In all cases of small cell carcinoma, however, S-100 protein-positive dendritic cells were rare. Electron microscopic study of two adenocarcinomas clearly demonstrated many Birbeck granules in the cytoplasm of S-100 protein-positive dendritic cells and confirmed that S-100 protein-positive cells in lung cancer were identical with Langerhans cells.     

Dengue fever virus and Japanese encephalitis virus synthetic peptides,with motifs to fit HLA class I haplotypes prevalent in human populations in endemic regions,can be used for application to skin Langerhans cells to prime antiviral CD8+ cytotoxic T cells (CTLs)—A novel approach to the protection of humans

Flaviviruses were reported to induce CD8⁺ cytotoxic T cells in infected individuals, indicating that nonapeptides, proteolytic cleavage products of the viral precursor protein, enter the endoplasmic reticulum in infected cells and interact with HLA class I molecules. The assembled HLA class I molecules are transported to the plasma membrane and prime CD8⁺ T cells. Current knowledge of the interaction of viral peptides with HLA molecules is reviewed. Based on this review, an idea is presented to use synthetic flavivirus peptides with an amino acid motif to fit with the HLA class I peptide binding group of HLA haplotypes prevalent in a given population in an endemic area. These synthetic viral peptides may be introduced into the human skin using a lotion containing the peptides (Peplotion) together with substances capable of enhancing the penetration of these peptides into the skin to reach Langerhans cells. The peptide-treated Langerhans cells, professional antigen-presenting cells, may bind the synthetic viral peptides by their HLA class I peptide-binding grooves. Antigens carrying Langerhans cells are able to migrate and induce the cellular immune response in the lymph nodes. This approach to the priming of antiviral CD8⁺ cytotoxic T cells may provide cellular immune protection from flavivirus infection without inducing the humoral immune response, which can lead to the shock syndrome in Dengue fever patients. To be able to develop anti-Dengue virus synthetic peptides for populations with different HLA class I haplotypes, it is necessary to develop computational studies to design HLA class I Dengue virus synthetic peptides with motifs to fit the HLA haplotypes of the population living in an endemic region for Dengue fever. Experiments to study Dengue virus and Japanese encephalitis peptides vaccines and their effectiveness in protection against Dengue fever and Japanese encephalitis are needed. The development of human antiviral vaccines for application of viral peptides in a lotion to human skin (Peplotion) may be useful and affordable for populations of developing countries.     

Inhibition of L-type calcium channels by internal GTP [γS] in mouse pancreatic β cells

Pretreatment of pancreatic cells with pertussis toxin resulted in a 30% increase in peak whole-cell Ca²⁺ currents recorded in the absence of exogenous intracellular guanine nucleotides. Intracellular application of 90 M GTP[S], by liberation from a caged precursor, resulted in 40% reduction of the peak Ca²⁺ current irrespective of whether the current was carried by Ca²⁺ or Ba²⁺. Effects on the delayed outward K⁺ current were small and restricted to a transient Ca²⁺-dependent K⁺ current component. Inhibition by GTP[S] of the Ca²⁺ current was not mimicked by standard GTP and could not be prevented either by pretreatment with pertussis toxin or by inclusion of GDP[S] or cyclic AMP in the intracellular medium. The inhibitory effect of GTP[S] could be counteracted by a prepulse to a large depolarizing voltage. A similar effect of a depolarizing prepulse was observed in control cells with no exogenous guanine nucleotides. These observations indicate that inhibition of cell Ca²⁺ current by G protein activation results from direct interaction with the channel and does not involve second-messenger systems. Our findings also suggest that the cell Ca²⁺ current is subject to resting inhibition by G proteins.     

Studies of intestinal lymphoid tissue

Summary Peroral jejunal mucosae from 32 patients with untreated DH were quantitated by computerized image-analysis in terms of surface (villous) and crypt epithelial volumes and their corresponding lymphoid infiltrates, together with lamina propria volumes, neutrophils, mast cells and basophils. Three distinctive patterns of mucosal abnormality were identified: (a) the infiltrative lesion in which normal villus epithelium was infiltrated by small, non-mitotic lymphocytes: (b) the hyperplastic type, in which crypt hyperplasia and hypertrophy together with lymphoid infiltration of crypt epithelium was additional to the infiltrative lesion, and in which lamina propria was swollen and contained modest neutrophilic and basophilic infiltration: and (c) the destructive lesion, identical to the classic celiac sprue appearances with effacement of villi, crypt hypertrophy and more intensive polymorph infiltration of lamina propria. These progressive lesions parallel those seen in experimental graft-versus-host reactions, so that the entire spectrum of changes described here in DH appear consistent with a cell-mediated mucosal response to gluten. The extent of mucosal abnormality was unrelated to individual HLA status.Supported by the Medical Research Council, England     

Parietal neurons encoding spatial locations in craniotopic coordinates

The receptive fields of visual neurons are known to be retinotopically arranged, and in awake animals they move with gaze, maintaining the same retinotopic location regardless of eye position. Here, we report the existence in the monkey parietal cortex of cells (called real-position cells) whose receptive field does not systematically move with gaze. These cells respond to the visual stimulation of the same spatial location regardless of eye position and therefore directly encode visual space in craniotopic instead of retinotopic coordinates.     

Zur cytologischen Ultrastruktur des Schleimhautstroma bei Enteropathien,insbesondere bei der idiopathischen Steatorrhoe

Zusammenfassung Es wird an Hand von Dünndarmbiopsien über mesenchymale Zellreaktionen bei Enteropathien, insbesondere bei der idiopathischen Steatorrhoe berichtet. Das Biopsiematerial eines unausgewählten Krankengutes wurde lupen- und lichtmikroskopisch sowie elektronenoptisch untersucht. Lediglich in der Gruppe der idiopathischen Steatorrhoe (coeliac sprue) fanden sich konstante Veränderungen. Die übrigen primären oder sekundären enteropathischen Affektionen sind histomorphologisch uncharakteristisch und inkonstant. Eine diagnostische Abgrenzung der einzelnen Krankheitsbilder ist von morphologischer Seite nicht möglich.Für die idiopathische Steatorrhoe sind eine subtotale Zottenatrophie (flat mucosa), eine signifikante Erhöhung interepithelial gelegener Lymphocyten (15,7% auf 1000 Epithelzellen bei Normwerten zwischen 7,0 und 7,5%) und eine massierte, vorweiegend plasmacelluläre und lymphocytäre Stromainfiltration kennzeichnend. Die Plasmazellen zeigen die morphologischen Kriterien der Stimulation, ein Teil der Lymphocyten die einer initialen Transformation. Auf Grund dieser Befunde wird eine mögliche immunologische Komponente im Ablauf der idiopathischen Steatorrhoe diskutiert. Auch die engen lymphoepithelialen Beziehungen könnten auf Immunphänomene hinweisen. Es muß offen bleiben, ob es sich bei den interepithelialen Lymphocyten um immunkompetente, immunologisch aktive oder um sog. Memory-Zellen handelt.

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On the cytological ultrastructure of the muscosal stroma of intestinal enteropathy, especially of idiopathic steatorrhoea

Summary This investigation was designed to study the reactions of mesenchymal cells in enteropathy by means of jejunal biopsies. The biopsy material was intentionally obtained from unselected patients and was studied with magnifying lens, light and electron microscopy. Uniform lesions were found only in coeliac disease. Other primary or secondary enteropathic diseases were associated with non-characteristic and variable histomorphological changes not allowing a definite classification.In idiopathic steatorrhoe the typical findings are: flat mucosa, a significant increase of lymphocytes in interepithelial spaces (15.7% in 1000 epithelial cells as compared to 7.0 to 7.5% normally), and an intense infiltration of the stroma by plasma cells and lymphocytes. Flat mucosa can be considered as a quantitatively specific sign in idiopathic steatorrhoe compared with findings in enteropathic disease of other etiology. Morphologically the plasma cells appear to be activated. Some of the lymphocytes seem to be in a state of initial transformation. Because of these findings the close contact of lymphocytes and epithelial cells suggest immunological factors determining the course of idiopathic steatorrhoe.Morphologically it can not be decided, however, if the interepithelially arranged lymphocytes are immunologically competent or active or if they have to be considered as a memorycell-type.

     

Activation of atrial muscarinic K+ channels by low concentrations ofβγ subunits of rat brain G protein

Effects of G protein subunits from rat brain on cardiac K⁺ channel was examined in single atrial cells of guinea-pig, using patch clamp techniques. We found that 10 pM concentration of rat brain subunits preparation could activate the atrial muscarine receptor-gated K⁺ channel (I_K.ACh). Neither the detergent, CHAPS, used to suspend nor the boiled preparation activated I_K.ACh. Furthermore, preincubation of subunits preparation in Mg²⁺-free solution, which easily inactivated -GTP-S, did not affect -activation of I_K.ACh. We concluded, therefore, that subunits themselves can activate I_K.ACh.Supported by the grants from the Ministry of Education, Culture and Science of Japan and from the Calcium Signal Workshop on Cardiovascular Systems