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H J Kuhn

Publications and source records attributed to H J Kuhn.

At least 19 recordsLinked to original sources
PubMed1997

Ciliogenesis in photoreceptor cells of the tree shrew retina.

Transmission electron microscopy of the retinal cones from several prenatal, young postnatal and adult tree shrews (Tupaia belangeri) reveals that the centrioles, from which the ciliary precursors of the outer segments grow out, are not transported into a pre-existing inner segment, but are positioned under the apical plasma membrane of cone precursor cells all through the inner segment formation. Ciliogenesis starts before or on embryonic day 20 and thus precedes initial formation of the inner segment by 20 days, which is half the gestation period. Thus, the maturation of the outer segment covers a considerably longer period than has been previously described. Published observations from other mammals can be interpreted as conforming with the situation in Tupaia. In other vertebrates, compared to mammals, marked heterochronies do occur. In Tupaia, the centrioles and the cilium are located close to the central longitudinal axis of the photoreceptor precursor cell from the 20-day-old embryo to the 5-day-old juvenile. In this position the microtubule apparatus originating from the centrioles should be most effective in transporting the mitochondria into the inner segment. In the 12-day-old tree shrew, when transport of the mitochondria into the inner segment has been completed, centrioles and cilium have shifted into an eccentric position and the light-collecting megamitochondria have approached the disks of the outer segment. This eccentric position is maintained in all later developmental stages. In certain of the retinal areas of the adult Tupaia, the connecting cilia of neighbouring cones are always positioned on the same side of the inner segments.

Animals↗
PubMed1997

"Lens mitochondria" in the retinal cones of the tree-shrew Tupaia belangeri.

In all mammals, the mitochondria of the cones of the retina are concentrated in the inner segment. Uniquely in tree-shrews (Tupaia, Scandentia, Mammalia), a "megamitochondrion" exhibiting highly specialized systems of densely packed cristae and a very electron dense matrix, is located apically in the inner segment. The ellipsoid is a solid body containing several megamitochondria and, towards its base, a large number of smaller mitochondria. The refractive index of isolated, but not oriented, inner segments of Tupaia belangeri is higher (XA = 1.405) than in any other mammal studied so far. The consistent geometrical pattern of the multilamellar crista-matrix systems, oriented longitudinally towards the outer segment, suggests an additional optical function of the megamitochondria.

Animals↗
PubMed1996

[Evaluation of the oscillometric blood pressure monitors: Dinamap 1846 and HP M-1008B].

Using the PTB simulator, which emits real signals from patients, we examined the precision of the oscillometric blood pressure measurement with the Dinamap 1846 (Critikon) and the HP M-1008B (Hewlett Packard). For this purpose we simultaneously registered invasive arterial pulsewave, cuff pressure and cuff pressure oscillations of 20 patients from our intensive care unit and stored them in the database of the simulator. The invasive reference blood pressure values were determined following the recommendations given by the Association for the Advancement of Medical Instrumentation. The invasive system showed a cut-off frequency of 35 Hz; the damping constant was 0.21. With 49 record signals from patients we carried out 15 simulated measurements each. From a total of 49 bio-signals from patients the Dinamap 1846 was able to process 41 signals and the HP M-1008B 47 signals. The mean error of the oscillometric blood pressure measurement of the systolic, diastolic and mean arterial pressure amounted to -2.50 mmHg, 3.35 mmHg (P < 0.05) and 1.51 mmHg with the Dinamap 1846 and to -8.5 mmHg (P < 0.001), -5.15 mmHg (P < 0.001) and -5.58 mmHg (P < 0.001) for the HP M-1008B. The 95% confidence limit for the systolic, diastolic and the mean arterial pressure amounts to 56 mmHg, 30 mmHg and 35 mmHg for the Dinamap 1846 and 50 mmHg, 38 mmHg and 35 mmHg for the HP M-1008B. The differences between that two instruments could be caused by the different algorithms for the calculation of blood pressure values and different artefact detection and elimination techniques. The results of the performance tests we achieved with the PTB simulator correspond to the results of other clinical examinations. The American Association for the Advancement of Medical Instrumentation recommends a maximum mean error of 5 +/- 8 mmHg. None of the examined instruments lay within these limits. Due to the systematic and stochastic errors, we think that the Dinamap 1846 (Critikon) and the HP M-1008B (Hewlett Packard) do not achieve performance levels that are adequate for measuring critically ill patients.

Adult↗
PubMed1996

Morphogenesis of megamitochondria in the retinal cone inner segments of Tupaia belangeri (Scandentia).

The morphogenesis of the megamitochondria in the retinal cones of prenatal, young postnatal and adult tree shrews (Tupaia belangeri) was studied by transmission electron microscopy and three-dimensional reconstruction techniques. The initial assembly of the supranuclear cone mitochondria and their subsequent migration towards the developing inner segment conform to the morphogenetic pattern known from other mammals. Within the first postnatal week, however, a marked increase in both the number of the cristae and the matrix density occurs in the inner segment mitochondria of Tupaia. These mitochondria then grow, initially exhibiting a basal-to-apical size-gradient. In the 17-day-old Tupaia, this gradient is superseded by a radial size-gradient that, in addition to the single apical megamitochondrion, is characteristically found in the adult Tupaia. The number of megamitochondria remains almost constant from day 12 of postnatal ontogenesis to the adult stage. Each megamitochondrion consists of an apically located body from which several long processes project towards the base of the inner segment. In the older stages, the number of small mitochondria that most probably have budded off from the megamitochondrial processes clearly increases. We consider that megamitochondria in the cone inner segments of Tupaia arise by the growth of a single mitochondrion and not by the fusion of smaller mitochondria.

Animals↗
PubMed1996

The role of microtubules and microtubule-organising centres during the migration of mitochondria.

The translocation of mitochondria towards the primitive inner segment of the cones in the tree shrew Tupaia belangeri was investigated by transmission electron microscopy. Throughout ontogeny the migrating mitochondria were codistributed with cytoplasmic microtubules which were preserved after the application of conventional preparation techniques for transmission electron microscopy. Both the basal body of the connecting cilium and the second centriole located in the vicinity of the basal body were demonstrated to act as microtubule-organising centres (MTOCs) from which axonemal and cytoplasmic microtubules originated. The megamitochondria in the inner segment of the retinal cones of Tupaia are unique among mammals with respect to their extraordinary size and to their ordered distribution characterised by longitudinal and radial size-gradients within developing and mature cone inner segments. Thus the consistent finding of microtubules and MTOCs in the structurally polarised cones represents an extreme example of the capacity of cells to regulate the transport and distribution of organelles.

Animals↗
PubMed1994

Embryological development of the arterial system of the forelimb in Tupaia.

BACKGROUND: The arterial system of the upper extremities in man shows drastic developmental changes and many individual variations related to interspecific variations in primates. The ontogenetic development in Tupaia was examined from the viewpoint of comparative embryology. METHODS: Histological specimens of 39 embryos were observed and reconstructed in three dimensions using a computer program. Four adult animals were dissected and examined with angiography to ascertain the end stage of development. RESULTS: At the proximal end of the upper arm the deep brachial artery appears first as a concomitant vessel with the radial nerve. It becomes reduced in size and is succeeded by the posterior circumflex humeral artery, which is accompanied initially by the axillary nerve and finally by the radial nerve. The main arterial passageway to the fingers consists of the brachial and interosseous arteries during early development. The superficial brachial artery and median artery are formed later, and their connection becomes the main route of blood supply for the finger arteries up to the adult stage. The ulnar artery is formed at the end of arterial development to form the ulnar end of the superficial palmar arch. The superficial antebrachial arteries are also recognized. CONCLUSIONS: All the arterial elements of the forelimb in Tupaia are observed in a variety of primates, including man, and the characteristics of Tupaia are thought to represent the primitive conditions of the common ancestor of tree shrews and primates.

Angiography↗
PubMed1994

The vomeronasal organ of the New World monkey Saguinus fuscicollis (Callitrichidae). A light and transmission electron microscopic study.

The vomeronasal organ (VNO) of the New World monkey Saguinus fuscicollis (Callitrichidae) is located at the base of the most distal portion of the nasal septum opening into the nasal portion of the ductus nasopalatinus which also communicates with the oral cavity. The lumen of the VNO is limited medially and laterally by a neuroepithelium which is devoid of intraepithelially located blood vessels and composed of receptor, supporting and basal cells. Ultrastructural analysis of the VNO of Saguinus fuscicollis reveals morphological features which lead one to postulate the functional capacity of this organ in these primates. A possible mechanism through which scent marks may be incorporated into the VNO is discussed.

Animals↗
PubMed1994

Postpartum erythrophagocytosis, iron storage and iron secretion in the endometrium of the tree shrew (Tupaia) during pregnancy.

Tree shrews (Tupaia belangeri) develop a bidiscoid endotheliochorial placenta. In addition, histiotrophe secreted by uterine glands is absorbed by the paraplacental trophoblast. Histiotrophe which is rich in iron is necessary for erythropoiesis in the young embryo. This report is part of a study of the accumulation and metabolism of iron in the endometrium of precisely dated pregnant Tupaia belangeri by application of electron spectroscopy and histochemistry. In the endometrium of tree shrews which had been pregnant at least once, iron-laden granules were present in macrophages and secreting cells of uterine glands. Iron accumulated in the endometrium shortly after parturition, when macrophages phagocytosed erythrocytes at small haematomas 0.2-0.5 mm in diameter. These haematomas arose during parturition after bleeding into the uterine stroma when the placental discs were detached. At 24 h after parturition the following structural consequences of the erythrolysosomal breakdown of phagocytosed erythrocytes could be observed: free cytosolic siderin granules, membrane-bound siderosomes, telolysosomes (some of which contained myelin figures or lipid droplets) and mixed telolysosomes (containing membranous stacks and siderin granules). During the lysosomal degradation of phagocytosed erythrocytes, iron was transferred from haemoglobin into a different macromolecular compound. Electron energy loss spectra detected from inside siderosomes indicated an iron-oxygen compound, and high-power bright field electron micrographs of siderosomes demonstrated the ultrastructural pattern characteristic of ferritin. At about d 12 of a new pregnancy, macrophages containing siderosomes closely approached the bases of secreting cells of endometrial glands. This strongly suggests that iron is transferred from the macrophages to the glandular cells. Within the glandular cells, iron-rich histiotrophe was synthesised and released into the glandular lumen. Within the uterine cavity this histiotrophe was absorbed by the omphalopleure. We suggest that among eutherians, postpartum erythrophagocytosis, the transfer of iron from macrophages to uterine glands, and the paraplacental uptake of iron, represent an ancestral mechanism of iron supply to the embryo.

Animals↗
PubMed1992

Effect of Ca2+ on weak cross-bridge interaction with actin in the presence of adenosine 5'-[gamma-thio]triphosphate).

In the presence of the nucleotide analog adenosine 5'-[gamma-thio]triphosphate (ATP[gamma S]), effects of Ca2+ on stiffness and equatorial x-ray diffraction patterns of single skinned fibers of the rabbit psoas muscle were studied. It is shown that cross-bridges in the presence of ATP[gamma S] have properties of the weak-binding states of the ATP hydrolysis cycle. Raising the Ca2+ concentration up to pCa 4.5 has little effect on actin affinity of cross-bridges in the presence of ATP[gamma S]. However, the rate constants for cross-bridge dissociation and reassociation from and to actin are reduced by about 2 orders of magnitude. In addition, nucleotide affinity of the cross-bridge is much smaller at high Ca2+ concentrations. Implications for interpretation of fiber stiffness recorded during isotonic shortening and the rising phase of a tetanus are discussed.

Actins↗
PubMed1990

Stretch-induced increase in the Ca2+ sensitivity of myofibrillar ATPase activity in skinned fibres from pig ventricles.

The increase in force development in the heart with increase in end-diastolic pressure (Frank-Starling mechanism) has been ascribed to an increase in contractile responsiveness of the myofibrils to calcium. We now show that this calcium sensitization is also associated with an increase in calcium responsiveness of the myofibrillar ATPase. Thus, at submaximal Ca activation (pCa 6.0), the ATPase activity of skinned fibres from pig right ventricles is increased from 57.9 +/- 4.4% to 70.6 +/- 4.4% of the maximal Ca2+ activation of ATPase by stretching (by 15% lo). At maximal Ca2+ activation, ATPase was barely altered by stretching. The relationship between ATPase activity of skinned trabecula of pig right ventricle and ATPase-Ca2+ concentrations is shifted (by 0.1 pCa unit) to higher pCa values after a stretch-induced increase of the sarcomere length from 2.1 microns to 2.4 microns. The relationship between force and pCa was affected in a similar way by extension. This increased calcium sensitivity is, however, not associated with an alteration in the relationship between ATPase activity and force development (tension cost). In accordance with Brenner's hypothesis, we propose therefore that stretch activation of ATPase is associated with an increase in the apparent rate constant of crossbridge attachment rather than with a decrease in the apparent rate constant of crossbridge detachment.

Adenosine Triphosphatases↗
PubMed1988

The early development of the epicardium in Tupaia belangeri.

Development of the epicardium was studied in embryos of Tupaia belangeri from the 13th to 15th day of ontogeny. The greater part of the epithelium of the epicardium does not differentiate locally from the myoepicardium (cardiac splanchnopleure, splanchnic mesoderm), but rather from the coelomic epithelium of the septum transversum. The myoepicardium of the future atria and ventricles differentiates into myocardial cells only. On ontogenetic day 13, bulbar protrusions (the "villi" of Kurkiewicz 1909) are formed on the surface of the septum transversum and extend into the pericardial cavity, primarily between the sinoatrial and the ventricular regions of the embryonic heart. These protrusions are covered by flattened interdigitating cells, and they are filled with intercellular fluid of the mesenchyme of the septum transversum. Many mitoses are found among the cells. From these protrusions free vesicles are formed which are discharged into the pericardial cavity. The vesicles attach to the surface of the myoepicardium, i.e. to the developing myocardial cells. The vesicles open, and their cells spread out onto the surface of the heart to form the primary epicardium. This process begins on the dorsal surface of the heart, close to the protrusions of the septum transversum, there are, however, further isolated patches of primary epicardium in other regions of the surface of the heart. After the epicardial cells have settled onto the myocardium, mitoses become rare among them. On day 15, most of the myocardium is coated by the primary epicardium and the protrusions on the septum transversum disappear. A "bare" myocardium, as found on ontogenetic days 12 and 13 in Tupaia, might be a primitive (plesiomorphic) condition among chordates. In adult Branchiostoma, the coelomic epithelium which coats the contractile blood vessels had been found to differentiate into muscle cells that remain uncoated on the side facing the coelomic cavity (Franz 1933; Joseph 1914, 1928).

Animals↗
PubMed1988

The dependence of isometric tension, isometric ATPase activity, and shortening velocity of limulus muscle on the MgATP concentration.

The dependence of the isometric tension, the velocity of unloaded shortening, and the steady-state rate of MgATP hydrolysis on the MgATP concentration (range 0.01-5 mM MgATP) was studied in Ca-activated skinned Limulus muscle fibers. With increasing MgATP concentration the isometric tension increased to a peak at approximately 0.1 mM, and slightly decreased in the range up to 5 mM MgATP. The velocity of unloaded shortening depended on the MgATP concentration roughly according to the Michaelis-Menten law of saturation kinetics with a Michaelis-Menten constant Kv = 95 microM and a maximum shortening velocity of 0.07 muscle lengths s-1; the detachment rate of the cross-bridges during unloaded shortening was 24 s-1. The rate of MgATP splitting also depended hyperbolically on the MgATP concentration with a Michaelis-Menten constant Ka = 129 microM and a maximum turnover frequency of 0.5-1 s-1. The results are discussed in terms of a cross-bridge model based on a biochemical scheme of ATP hydrolysis by actin and myosin in solution.

Adenosine Triphosphatases↗
PubMed1987

The early development of the heart of Tupaia belangeri, with reference to other mammals.

The development of the heart of Tupaia belangeri from the first endothelial-lined lumina to the cardiac loop is described in 20 embryos with 2 to 14 somites, from ontogenetic days 11 and 12. Bilateral endocardial tubes transporting blood are found in the 8-somite embryo; in the middle cardiac plate, angioblasts and angiocysts are located between them. In the 9-somite embryo, formation of the cardiac loop has started, the endocardial tubes approach each other closely, most of the angiocysts have been incorporated by the expanding endocardial tubes, and fusion of the endocardial lumina has started in the cono-truncal area. Apparently, much of the endocardial cardiac loop found in the 9-somite embryo has been produced by the disproportionate lengthening of a segment of the endocardial tubes, which is very short in the 8-somite embryo. In the 13-somite embryo the endocardial tubes have largely fused, but tube-like strands of endothelia, remnants of the original endothelial walls separating them, form a "palisade" and mark the original boundary between them. Myoepicardial differentiations of the splanchnopleure begin separately on both sides of the embryo and gradually spread craniad until they coalesce in the midline, in front of the anterior intestinal portal. The caudal portions of the endocardial tubes with initial myoepicardial and cardiac jelly differentiations do not contribute to the definitive heart. The anterior intestinal portal is very broad in Tupaia. Contradictions in the literature as to the bilaterality of cardiac primordia of eutherian mammals are discussed. The hypothesis is developed that bilateral endocardial tubes and bilateral myoepicardial differentiations of the splanchnopleure develop in species with a large yolk-sac, relatively late closure of the foregut, and a broad anterior intestinal portal (e.g., Tupaia, ferret, and cat, etc.). This is probably the primitive condition in eutherian mammals. In species with a small yolk-sac and/or reversal of germ layers (man, rodents), the foregut and anterior intestinal portal are formed earlier, the heart primordium reaches its median position ventral to the foregut in the angiocyst-stage, and the first endocardial lumina appear close to the midline. In these species, the primordium of the endocardium seems to be plexiform and without clear evidence for bilaterality.

Animals↗
PubMed1986

[Clarification of basic factors of the morphology of the skull, especially ontogenesis of the skull of Cavia aperea f. porcellus L].

Skull morphology cannot be understood without consideration of its ontogenetic morphogenesis. Meaningful comparisons of vertebrate crania must include these developmental processes. The criteria and methods for descriptions and comparisons were originally established by Ernst Gaupp and others around the beginning of this century. Nevertheless, the complete course of cranial morphogenesis from the first precartilaginous blastemata to the adult cranium has never been described in any vertebrate species, so far. Dierbach (1985a, b) intended to contribute to the knowledge of morphogenesis of the cranium of Cavia. His paper is based on a deficient reconstruction of the cranium of an embryo of 36 mm crown-rump-length. As the description follows Zimmerman's (1976) description of an 55 mm CRL-stage, the characteristics of the 36 mm stage are missed. New findings are not reported. The paper does not include reconstruction of the process of morphogenesis of the cranium or of any of its structures. A new morphological interpretation of the Foramen infraorbitale of Cavia is not substantiated. Literature is cited unreliably. For comparisons with other species or for the reconstruction of cranial morphogenesis of Cavia on the basis of the results of several previous authors Dierbach's papers cannot be used, because of many inconsistencies in terminology and definitions. Frick (1954) and Zeller (1983), both cited by Dierbach, partially differ in their respective interpretation of the morphogenesis of the Fenestra rotunda of mammals. Dierbach's discussion does not proceed beyond Voit (1909). Morphology of the Ala temporalis is discussed controversially in recent papers. Dierbach remains at the state of knowledge of Gaupp (1902). Authors such as Broom (1908), Fuchs (1915), and Gregory (1913) already have shown that the palatoquadrate participates in the formation of the Ala temporalis of mammals. The alisphenoid can be recognized in fig. 3 of Dierbach (1985 a). However, it is not mentioned in the caption or in the text. Therefore, the problem of the secondary lateral wall of the braincase of mammals in the orbitotemporal region of the skull cannot be discussed by Dierbach. No problems of cranial morphology are raised or discussed.

Animals↗
PubMed1985

The effect of MgATP on forming and breaking actin-myosin linkages in contracted skinned insect flight muscle fibres.

At neutral pH, fully Ca2+ -activated glycerinated dorsal longitudinal fibre bundles from Lethocerus indicus contract under isometric conditions and respond to release by deactivation, i.e. quick release causes a delayed tension fall. At slightly alkaline pH, the release-induced deactivation becomes a transient phenomenon, i.e. a delayed tension fall is followed by a slow tension recovery. This enabled us to study the effect of MgATP concentration on the phases of deactivation and slow recovery. Reduction of the MgATP concentration slows down the tension response to a quick length change and increases the time constants of the delayed deactivation phase and of the slow recovery phase. The rate constants depend on the ATP concentration according to the Michaelis-Menten law yielding apparent dissociation constants (Km) of 2 mM and 0.09 mM and maximal rate constants of 700 s-1 and 20 s-1 for the deactivation phase (crossbridge detachment) and slow recovery phase (crossbridge reattachment) respectively. The rate of MgATP hydrolysis is also hyperbolically related to the MgATP concentration (Km = 0.14 mM, maximal MgATP turnover rate 1.2 s-1. It is concluded that the effect of MgATP on the deactivation phase, in which crossbridges dissociate strain dependent from the actin, is controlled by at least two mechanisms: (1) fast equilibrium transitions within attached crossbridge states which augment MgATP dissociation from crossbridges with discharged elastic elements; and (2) a crossbridge strain-dependent isomerization of the ternary actin-myosin-MgATP complex which determines crossbridge detachment from the actin.

Actins↗
PubMed1984

Tension transients in skinned muscle fibres of insect flight muscle and mammalian cardiac muscle: effect of substrate concentration and treatment with myosin light chain kinase.

Glycerinated single fibres from the dorsal longitudinal muscle of Lethocerus maximus were isometrically contracted in MgATP-salines (10 microM Ca2+; 1.5 mM Mg2+; pH 6.7; 22 degrees C and 20 mM PEP; 100 U/ml pyruvate kinase). The ratio of ATPase activity to tension decreased by a factor of 2 after reducing the ATP-concentration from 15 to 0.5 mM. At all ATP-concentrations (0.5-15 mM), the fibres showed tension adjustments in response to small step changes in length characteristic to an actively contracting muscle: i) an elastic phase which did not depend on ATP-concentration ii) a quick phase of stress relaxation with at least two exponential components; iii) a phase of delayed tension generation. An increase in size of the length step and/or a decrease of ATP-concentration slowed the quick phase and the delayed phase. Similar results have been obtained with skinned cardiac muscle (pig right ventricle). To see, how the isolated contractile system is affected by an increase in the light chain phosphorylation, tension transients were studied in skinned right ventricular muscle fibres before and after incubation with ATP gamma S (2 mM), pure myosin light chain kinase (9 micrograms/ml), Calmodulin (1 microM) and Ca2+ (0.8 microM). While isometric tension development elicited by 20 microM Ca2+ in the ATP salt solution was barely affected in presence of the enzyme, the ATPase activity was decreased by about 25% of the control. There was also a marked decrease (about 50%) in the contraction velocity as determined by the recovery of tension following a quick release. Quick stretches cause an immediate increase in tension followed by a rapid fall and a subsequent rise in tension. The velocity of this tension rise decreased by approximately 30% after incubation with myosin light chain kinase.

Adenosine Triphosphate↗
PubMed1982

Decrease in stiffness during shortening in calcium activated skinned muscle fibers.

Single fibers from frog sartorius or semitendinosus muscle were mechanically skinned and activated in ATP salt solution containing 10 micro M Ca2+ (7 degrees C). After development of an isometric contraction, fibers were released at constant speed (0.03-2.4 s-1). During ramp shortening, stiffness was determined from the slope of the tension-length diagram obtained during superimposed quick stretches. Both force and stiffness decreased, as the ramp shortening proceeded and approached a steady value after about 60 ms. An increase in speed of shortening caused a decrease in fiber tension and stiffness and an increase in the ratio of stiffness to tension, suggesting a decrease in both the number of attached crossbridges and in the average force per crossbridge.

Animals↗