Das Zusammenspiel von Lagena und Utriculus bei der Lageorientierung der Knochenfische

Zusammenfassung Aus früheren Versuchen an Fischen ergab sich, daß die eine Lageorientierung ermöglichenden Organe (Utriculi und Augen) sich in ihrer Wirkung im Zentrum linear überlagern, während die nach einseitiger Utriculusausschaltung bewirkte zusätzliche Drehtendenz von der linearen Superposition in einem bestimmten Bereich stark abweicht.Die Hypothese, daß diese Abweichung durch einen Einfluß der Lagena verursacht ist, wird bestätigt: nach beidseitiger Lagenaausschaltung verschwindet die Abweichung quantitativ.Utriculus- und Lagenaausschaltung in verschiedener Kombination klären die Rolle der Lagena weiter auf; die Hauptergebnisse sind auf S. 567 (1–5) zusammengestellt. Es zeigt sich im ganzen, daß die Lagena zwar Schwererezeptoren besitzt, aber für sich allein keine Lageorientierung ermöglicht. Sie hat eine, in ihrer Größe lageabhängige, tonisierende Wirkung auf das gleichseitige Gleichgewichtszentrum, durch die Aktivitätsunterschiede in beiden Zentren (bei Normallage des Tieres) ausgeglichen werden.Es wird gezeigt, daß diese Mitarbeit am Gleichgewicht biologisch sinnvoll, aber wohl nur eine Nebenleistung der Lagena ist.Im Gegensatz zum Lagenaeffekt bewirken alle Aufregung verursachenden Reize eine multiplikative Steigerung vorhandener Aktivitätsunterschiede im Gleichgewichtszentrum. Auch dieser Effekt erweist sich als eine biologisch sinnvolle Sicherungsmaßnahme.Fische ohne Utriculi und Lagenae besitzen noch eine sehr ungenaue Beziehung zur Erdschwere, die vermutlich durch Propriozeptoren der Schwanzmuskeln vermittelt wird.Als Nebebenbefund ergibt sich, daß Utriculusstatolithenregenerate von oft ganz abstrusen Formen noch eine völlig normale, nur quantitativ schwächere Orientierung zur Erdschwere ermöglichen; daraus wird geschlossen, daß Form und Beschaffenheit des Statolithen für seine Funktion weitgehend belanglos sind.     

Lysis of murine B lymphoma cells by transgenic phagocytes via a human FcγRI×murine MHC class II bispecific antibody

 The class I IgG receptor (FcγRI) on cytotoxic effector cells has been reported to initiate destruction of tumour cells by effector cells in vitro. We are aiming at developing an immunocompetent model to evaluate the cytotoxic capacity of human FcγRI for the rejection of tumour cells in vivo. Therefore, we recently generated a transgenic mouse strain expressing human FcγRI on monocytes, macrophages, and neutrophils. In these mice, the human receptor is up-regulated by granulocyte-colony-stimulating factor (G-CSF) and is able to trigger cellular responses. Subsequently, in the present study the B cell lymphoma IIA1.6 cell line is selected as a tumour target, and a human FcγRI-directed antitumour bispecific antibody (bsAb) is constructed and characterized. Fab′ fragments of mAb 22, which bind hFcγRI at an epitope that is distinct from the ligand binding site, were chemically linked to Fab′ fragments of rat anti-(mMHC class II antigens) mAb M5/114, yielding bsAb 22×M5/114. This bsAb was able to bind simultaneously to hFcγRI and mMHC class II antigens in a dose-dependent fashion. Binding of 22×M5/114 to FcγRI was not inhibited in the presence of human IgG. It is important to note that, MHC-class-II-expressing IIA1.6 lymphoma cells were lysed by whole blood from G-CSF-treated transgenic mice in the presence of bsAb 22×M5/114. No lysis by whole blood from non-transgenic mice or from transgenic animals that had not received G-CSF was observed. These results indicate that human FcγRI is able to mediate lysis of murine IIA1.6 lymphoma cells by transgenic effector cells via bsAb 22×M5/114. A trial with transgenic mice, evaluating the efficacy of these hFcγRI-directed bsAb in combination with G-CSF for treatment of IIA1.6 B cell lymphoma, is currently in progress. Accepted: 14 October 1997     

Evidence for Nitric Oxide Mediated Effects on Islet Hormone Secretory Phospholipase C Signal Transduction Mechanisms

We have investigated the putative role of nitric oxide (NO) as a modular of islet hormone release, when stimulated by the muscarinic receptor agonist–phospholipase C activator, carbachol, with special regard to whether the IP₃-Ca²⁺ or the diacylglycerol-protein kinase C messenger systems might be involved. It was observed that the NO synthase (NOS) inhibitor N^G-nitro-L-arginine methylester (L-NAME) markedly potentiated insulin release and modestly inhibited glucagon release induced by carbachol. Similarly, insulin release induced by the phorbol ester TPA (protein kinase C activator) was markedly potentiated. Glucagon release, however, was unaffected. Dynamic perifusion experiments with ⁴⁵C²⁺-loaded islets revealed that the inhibitory action of L-NAME on carbachol-stimulated NO-production was reflected in a rapid and sustained increase in insulin secretion above carbachol controls, whereas the ⁴⁵Ca²⁺-efflux pattern was similar in both groups with the exception of a slight elevation of ⁴⁵C²⁺ in the L-NAME-carbachol group during the latter part of the perifusion. No difference in either insulin release or ⁴⁵Ca²⁺-efflux pattern between the carbachol group and L-NAME-carbachol group was seen in another series of experiments with identical design but performed in the absence of extracellular Ca²⁺ . However, it should be noted that in the absence of extracellular Ca²⁺ both ⁴⁵Ca²⁺-efflux and, especially, insulin release were greatly reduced in comparison with experiments in normal Ca²⁺. Further, in the presence of diazoxide, a potent K⁺ _ATP-channel opener, plus a depolarizing concentration of K⁺ the NOS-inhibitor L-NAME still markedly potentiated carbachol-induced insulin release and inhibited glucagon release. The enantiomer D-NAME, which is devoid of NOS-inhibitory properties, did not affect carbachol-induced hormone release. TPA-induced hormone release in depolarized islets was not affected by either L-NAME or D-NAME. The pharmacological intracellular NO donor hydroxylamine dose-dependently inhibited insulin release stimulated by TPA. Furthermore, a series of perifusion experiments revealed that hydroxylamine greatly inhibited carbachol-induced insulin release without affecting the ⁴⁵Ca²⁺-efflux pattern. In summary, our results suggest that the inhibitory effect of NO on carbachol-induced insulin release is not to any significant extent exerted on the IP₃-Ca²⁺ messenger system but rather through S-nitrosylation of critical thiol-residues in protein kinase C and/or other secretion-regulatory thiol groups. In contrast, the stimulating action of NO on carbachol-induced glucagon release was, at least partially, connected to the IP₃-Ca²⁺ messenger system. The main effects of NO on both insulin and glucagon release induced by carbachol were apparently exerted independently of membrane depolarization events.     

Regulation of adenylate cyclase in electropermeabilized Dictyostelium discoideum cells.

In Dictyostelium discoideum cells the enzyme adenylate cyclase is functionally coupled to cell surface receptors for cAMP. Coupling is known to involve one or more G-proteins. Receptor-mediated activation of adenylate cyclase is subject to adaptation. In this study we employ an electropermeabilized cell system to investigate regulation of D. discoideum adenylate cyclase. Conditions for selective permeabilization of the plasma membrane have been described by C.D. Schoen, J. C. Arents, T. Bruin, and R. Van Driel (1989, Exp. Cell Res. 181, 51-62). Only small pores are created in the membrane, allowing exchange of exclusively low molecular weight substances like nucleotides, and preventing the loss of macromolecules. Under these conditions functional protein-protein interactions are likely to remain intact. Adenylate cyclase in permeabilized cells was activated by the cAMP receptor agonist 2'-deoxy cAMP and by the nonhydrolyzable GTP-analogue GTP gamma S, which activates G-proteins. The time course of the adenylate cyclase reaction in permeabilized cells was similar to that of intact cells. Maximal adenylate cyclase activity was observed if cAMP receptor agonist or GTP-analogue was added just before cell permeabilization. If these activators were added after permeabilization adenylate cyclase was stimulated in a suboptimal way. The sensitivity of adenylate cyclase activity for receptor occupation was found to decay more rapidly than that for G-protein activation. Importantly, the adenylate cyclase reaction in permeabilized cells was subject to an adaptation-like process that was characterized by a time course similar to adaptation in vivo. In vitro adaptation was not affected by cAMP receptor agonists or by G-protein activation. Evidently electropermeabilized cells constitute an excellent system for investigating the positive and negative regulation of D. discoideum adenylate cyclase.     

PATTERN OF PHENOTYPIC VIABILITY AND FECUNDITY SELECTION IN A NATURAL POPULATION OF IMPATIENS PALLIDA

Estimates of viability and fecundity selection of 13 phenotypic characters for 1,536 individuals of Impatiens pallida growing in 24 locations within a single natural population were compared. Directional viability selection of cotyledon area, day of initial leaf production, number of leaves, and stem length was detected throughout this population. Directional fecundity selection of cotyledon area, day of initial flower production, number of leaves present on day of initial flower production, stem length on day of initial flower production, number of leaves, and stem length was also detected. Phenotypic selection of these characters was strong in some cases, and the strength of selection was significantly heterogeneous among locations. For several of the characters, directional phenotypic selection within the population was significantly positive in some locations and significantly negative in others separated by only a few meters. Fecundity selection was stronger than viability selection for some characters, implying that fecundity selection was at least as important as viability selection within this population. Soil moisture levels and light intensities played a larger role than soil nutrient levels in determining the patterns of both viability and fecundity selection, and differences in directional viability selection were more strongly related to environmental variation than were differences in fecundity selection. The pattern of phenotypic selection could not be reliably inferred from the patterns of mortality and reproduction alone.     

Benzolactam growth hormone secretagogues: Replacement of the C-3 amide bond in L-692,429

The synthesis and structure-activity relationships of various C-3 amide bond modifications in the novel nonpeptidyl growth hormone secretagogue L-692,429 are described. Several C-3 amide surrogates were prepared and the urea moiety was found to exhibit growth hormone releasing activity similar to that observed with L-692,429.