Biomedical subjects

K Lohmann

Publications and source records attributed to K Lohmann.

At least 19 recordsLinked to original sources

PubMed2001

Overexpression of human cardiac troponin in Escherichia coli: its purification and characterization.

All three subunits of the human cardiac troponin complex (cTn), namely the major isoform of the tropomyosin binding subunit (hcTnT3), the inhibitory subunit (cTnI), and the calcium binding subunit (cTnC), have been coexpressed in Escherichia coli. The cDNAs of each subunit have been cloned into the pSBET vector and transformed into E. coli. The coexpressed subunits assembled within the bacterial cells to form the hcTn complex (hcTnT3.hcTnI.hcTnC). The complex was isolated and purified by three chromatographic steps. Per 6-L cell culture about 10 mg of a highly purified troponin complex showing the expected 1:1:1 molar ratio of hcTnT3:cTnI:cTnC was obtained. Upon phosphorylation by protein kinase A at Ser22 and Ser23 in cTnI, this recombinant troponin complex shows a nearly identical (31)P NMR spectrum to the native one isolated from bovine heart. By measuring the rate of myosin S1 binding to reconstituted thin filaments it was shown that the dependence of the regulation of S1 binding upon calcium concentration and bisphosphorylation was comparable to the native complex.

Amino Acid Sequence↗

PubMed2000

Investigation of a truncated cardiac troponin T that causes familial hypertrophic cardiomyopathy: Ca(2+) regulatory properties of reconstituted thin filaments depend on the ratio of mutant to wild-type protein.

Familial hypertrophic cardiomyopathy (HCM) is caused by mutations in at least 8 contractile protein genes, most commonly beta myosin heavy chain, myosin binding protein C, and cardiac troponin T. Affected individuals are heterozygous for a particular mutation, and most evidence suggests that the mutant protein acts in a dominant-negative fashion. To investigate the functional properties of a truncated troponin T shown to cause HCM, both wild-type and mutant human cardiac troponin T were overexpressed in Escherichia coli, purified, and combined with human cardiac troponins I and C to reconstitute human cardiac troponin. Significant differences were found between the regulatory properties of wild-type and mutant troponin in vitro, as follows. (1) In actin-tropomyosin-activated myosin ATPase assays at pCa 9, wild-type troponin caused 80% inhibition of ATPase, whereas the mutant complex gave negligible inhibition. (2) Similarly, in the in vitro motility assay, mutant troponin failed to decrease both the proportion of actin-tropomyosin filaments motile and the velocity of motile filaments at pCa 9. (3) At pCa 5, the addition of mutant complex caused a greater increase (21.7%) in velocity of actin-tropomyosin filaments than wild-type troponin (12.3%). These data suggest that the truncated troponin T prevents switching off of the thin filament at low Ca(2+). However, the study of thin filaments containing varying ratios of wild-type and mutant troponin T at low Ca(2+) indicated an opposite effect of mutant troponin, causing enhancement of the inhibitory effect of wild-type complex, when it is present in a low ratio (10% to 50%). These multiple effects need to be taken into account to explain the physiological consequences of this mutation in HCM. Further, these findings underscore the importance of studying mixed mutant:wild-type preparations to faithfully model this autosomal-dominant disease.

Actins↗

PubMed1999

Characterization of the cardiac holotroponin complex reconstituted from native cardiac troponin T and recombinant I and C.

Cardiac troponin I (cTnI), the inhibitory subunit of cardiac troponin (cTn), is phosphorylated by the cAMP-dependent protein kinase A at two adjacently located serine residues within the heart-specific N-terminal elongation. Four different phosphorylation states can be formed. To investigate each monophosphorylated form cTnI mutants, in which each of the two serine residues is replaced by an alanine, were generated. These mutants, as well as the wild-type cardiac troponin I (cTnI-WT) have been expressed in Escherichia coli, purified and characterized by isoelectric focusing, MS and CD-spectroscopy. Monophosphorylation induces conformational changes within cTnI that are different from those induced by bisphosphorylation. Functionality was assessed by measuring the calcium dependence of myosin S1 binding to thin filaments containing reconstituted native, wild-type and mutant cTn complexes. In all cases a functional holotroponin complex was obtained. Upon bisphosphorylation of cTnI-WT the pCa curve was shifted to the right to the same extent as that observed with bisphosphosphorylated native cTnI. However, the absolute values for the midpoints were higher when recombinant cTn subunits were used for reconstitution. Reconstitution itself changed the calcium affinity of cTnC: pCa50-values were higher than those obtained with the native cardiac holotroponin complex. Apparently only bisphosphorylation of cTnI influences the calcium sensitivity of the thin filament, thus monophosphorylation has a function different from that of bisphosphorylation; this function has not yet been identified.

Animals↗

PubMed1999

Pressure-dependent renin release: effects of sodium intake and changes of total body sodium.

The impact of sodium intake and changes in total body sodium (TBS) for the setting of pressure-dependent renin release (PDRR) was studied in freely moving dogs. An aortic cuff allowed servo control of renal perfusion pressure (RPP) at preset values. Protocols were 1) high sodium intake (HSI), 2) low sodium intake (LSI), 3) TBS moderately increased (+3.1 mmol Na/kg body wt) by 20% reduction of RPP for 2-4 days, 4) large increase of TBS (+8.2) by combining protocol 3 with aldosterone infusion, and 5) TBS reduced (-3.1) by peritoneal dialyses. Twenty-four-hour time courses of arterial plasma renin activity (PRA) revealed that LSI increased PRA for the first 10 h only; afterward PRA did not differ between LSI and HSI. Reduced TBS increased PRA constantly, and the large increase of TBS constantly reduced PRA. PDRR stimulus-response curves (assessed 20 h after last sodium intake) revealed an exponential relationship in each protocol. PDRR was not changed by different sodium intake. Conversely, reduced TBS increased PDRR markedly, whereas the large increase of TBS suppressed it. Thus an inverse relationship between TBS and PRA, i.e., a TBS-dependent renin release, was found. This relationship was enhanced by decreasing RPP. This interplay between TBS-dependent renin release and PDRR allows the organism a differentiated reaction to changes in TBS and arterial pressure.

Animals↗

PubMed1999

Nerve transplantation: a father's final gift.

Offering the option of organ and tissue donation to grieving families may seem stressful, but asking the question may provide a positive means to extend care to the bereaved family and help others in return. Many donor families have said donation was an opportunity to make some sense out of a senseless situation and to relieve some of the grief they experienced. This article presents a case that started with such a discussion by ICU nurses in one of our donor hospitals, and ended with successful organ and tissue recovery and transplantation. As "routine" as this may sound, it was anything but routine--it made history.

Adult↗

PubMed1998

A new method for reliable and efficient reconstruction of 3-dimensional images from autoradiographs of brain sections.

Valuable information on metabolism and function of distinct brain regions can be extracted from autoradiographs of 2D brain sections, e.g. after labelling with the non-metabolisable sugar derivate [14C]-2-fluoro-deoxyglucose (2-FDG). For a more complete comprehension of the data and for a comparison with information obtained by modern functional imaging techniques it is essential to have a reliable and efficient method for the 3D reconstruction of autoradiographs of serial sections. This paper describes a new method for the alignment of 2D 2-FDG images, that combines two established algorithms, i.e. principal axes alignment followed by consistent matrix transformation. The power and efficiency of this new 2-step method is compared to those of various previously described procedures.

Algorithms↗

PubMed1998

BrainView: a computer program for reconstruction and interactive visualization of 3D data sets.

A computer program, BrainView, is presented which has been developed to reconstruct, visualize, and evaluate three dimensional (3D) biological and medical imaging data, such as images from histological sections, confocal microscopy, or magnetic resonance tomography. The program allows the simultaneous display of three orthogonal sectional planes, i.e. the horizontal, frontal, and sagittal planes, of reconstructed data and to move interactively through the brain to optimally assess the 3D data set. Furthermore, any arbitrary sectioning plane through a data set can be visualized. Implemented warping algorithms allow the geometric normalization of data sets of different animals, modalities or developmental stages as a preprocessing for the comparative evaluation of the data. For a quantitative analysis, data sets can be segmented based on equal grey levels and the corresponding equidensities were calculated. The program works on Apple-Macintosh computers and has a user-friendly graphical interface. The BrainView program is discussed in comparison to related programs.

Animals↗

PubMed1998

A model for the function of the bisphosphorylated heart-specific troponin-I N-terminus.

Bisphosphorylation of two adjacently located serine residues in the heart-specific N-terminus of the cTnl subunit reduces calcium affinity of the cTnC subunit. An interaction of the phosphorylation region of cTnI with acidic residues of another cTn subunit has been proposed formerly based on 31P nuclear magnetic resonance (NMR) data. A possible candidate is cTnC. Thus, an interaction model of cTnC with the bisphosphorylated cTnI N-terminus has been built using a homology model of hcTnC based on the crystal structure of tusTnC and the structure of the phosphorylation region of cTnI determined by 2D NMR. By computational search, five cluster of acidic residues of cTnC might interact with the cTnI phosphorylation region. Three sites could be excluded by 31P-NMR experiments. The two remaining sites are located in the N-terminal helix of cTnC and between calcium binding sites III and IV. Reorientation of the arginine and phosphoserine sidechains within the phosphorylation region as proposed by refined docking could explain the formerly measured changes in pKaapp values. Thus, local pKa changes might lead to the reduction of calcium affinity observed upon cTnI bisphosphorylation.

Amino Acid Sequence↗

PubMed1996

Changes of blood pressure, sodium excretion and sodium balance due to variations of the renin-angiotensin-aldosterone system.

UNLABELLED: Studies were performed in partly free moving Beagle dogs, kept under standardized environmental and dietetic conditions (food intake: once daily at 8:30 a.m., 5.5 mmol Na/kg body weight per 24 h). The dogs were chronically instrumented with an inflatable cuff around the aorta above the renal arteries, two aortic catheters above and below the cuff, and a bladder catheter. Three protocols were performed in 7 dogs each: (i) CONTROL: urine collection in 20-min intervals and measurement of Na excretion, continuous registration of mean arterial blood pressure (MABP) and heart rate for 4 consecutive days. (ii) As (i), but additional servocontrolled reduction of the renal perfusion pressure (rRPP) to stimulate renin secretion and the formation of angiotensin II and aldosterone. (iii) As (ii), but additional constant infusion of the angiotensin converting enzyme inhibitor Captopril. Despite rRPP Na is only transiently retained (pressure escape). MABP level is elevated, as long as total-body Na is augmented. In protocol iii no Na retention occurs, indicating that rRPP per se causes no Na retention. MABP level remained unchanged. Independent of the preset MABP level similar diurnal variation in MABP are present in all protocols. During control days major amounts of Na are excreted postprandially. Up to 5:00 p.m. 65% of the daily Na intake is excreted. After disturbance of Na control (protocols ii and iii) the Na excretion is shifted to the evening and night. Probably due to this shift Na retention can be prevented. Furthermore, these results demonstrate that rRPP-induced increases of total body Na and MABP are solely mediated by the activation of the renin-angiotensin-aldosterone system.

Animals↗

PubMed1996

Transvaginal ultrasonography of pelvic masses: evaluation of B-mode technique and Doppler ultrasonography.

OBJECTIVE: The purpose of this study was to evaluate pelvic masses by B-mode and Doppler ultrasonography for identification of ovarian malignancies. STUDY DESIGN: A previously described scoring system for pelvic masses was applied in 310 women, and the lesions were classified into four groups according to the ultrasonographic structure. Pulsatility index values of vessels within the tumor and the contralateral ovary and of both uterine arteries were determined. RESULTS: A total of 259 masses were benign and 51 were malignant. The scoring system and classification into morphologic groups revealed similar sensitivity, specificity, and positive and negative predictive values. Intratumoral and opposite ovarian blood flow and ipsilateral and contralateral uterine blood flow did not differ in benign and malignant masses except in cases of benign lesions in postmenopausal women. In malignant lesions a lower pulsatility index (0.94 +/- 0.4) was measured than in benign lesions (1.06 +/- 0.4, p < 0.05), although a remarkable overlap was found. CONCLUSION: The results suggest that further refinement of assessment of pelvic masses with Doppler ultrasonography is needed.

Adnexal Diseases↗

PubMed1996

Orientation and open-sea navigation in sea turtles

Loggerhead sea turtle hatchlings (Caretta caretta L.) emerge from underground nests, scramble to the sea and begin a transoceanic migration by swimming away from their natal beach and into the open ocean. Evidence suggests that hatchlings sequentially use three different sets of cues to maintain orientation during their initial migration offshore. While on the beach, hatchlings find the ocean by crawling towards the lower, brighter seaward horizon and away from the dark, elevated silhouettes of vegetation and dunes. Upon entering the ocean, turtles initially orient seawards by swimming into waves, which can be detected as orbital movements from under water. Laboratory experiments have demonstrated that turtles can transfer a course initiated on the basis of waves or visual cues to a course mediated by a magnetic compass. Thus, by setting a magnetic course on the basis of nearshore cues that indicate the seaward direction, hatchlings may continue on offshore headings after entering deep water beyond sight of land. Sea turtles may use the earth's magnetic field not only as a cue for compass orientation but also as a source of world-wide positional information. Recent experiments have demonstrated that loggerheads can detect subtle differences in magnetic field inclination and intensity, two geomagnetic features that vary across the surface of the earth. Because most nesting beaches and oceanic regions are marked by a unique combination of these features, these findings raise the possibility that adult sea turtles navigate using a bicoordinate magnetic map.

Journal Article↗

PubMed1996

[Multiple chemical sensitivity disorder in patients with neurotoxic illnesses].

The data of 466 subjects suffering from neurologic disorders which are suggested to be caused by neurotoxic agents in their environment retrospectively was evaluated and documented. Among these cases there were 151 subjects with symptoms of Multiple Chemical Sensitivity Disorder (MCSD). The relationship between the neurological health impairments and neurotoxic agents in the environment of these patients was characterised using five different categories (probable = A, possible = B, uncertain = C, unclarified = D, not probable = E). From the 466 patients 320 subjects (69%) could be assigned to the categories A and B, respectively. Within theses 320 cases with chronic neurotoxic health impairments 136 subjects (79 females and 57 males) showed signs of MCSD. Age and gender of cases as well as duration and character of exposure to neurotoxic substances retrospectively were assessed from the explicit files of the patients, which had been made anonymous for this purpose. Frequency of characteristic symptoms of neurotoxicity were analysed. Results are given for patients with neurotoxic health impairments with MCSD (n = 136) and without MCSD (n = 184). Neurotoxic substances which were used as indoor wood preservatives (mainly Pentachlorophenol and/or Lindane) were found to be the causative agents in 63% of the cases with neurotoxic health impairments and MCSD. Other important neurotoxic substances to which the patients were mainly exposed were organic solvents (25%), formaldehyde (15%), dental materials (15%), pyrethroides (13%), and other biocides (19%) (multiple exposures were possible). The time of exposure was calculated as being > or = 10 years for 55% of the patients with MCSD and for 50% of the group with neurotoxic health impairments but without MCSD. Out of the 184 cases with neurotoxic health impairments but without MCSD there were 22%, and out of the 136 cases with MCSD there were 39% who showed all symptoms of chronic fatigue syndrome. 53% of the cases with MCSD had an allergic disposition compared to only 20% of the cases without MCSD. This work is not a controlled epidemiological study but a retrospective documentation and evaluation of data related to environmental medicine. With the present documentation in this purely descriptive manner the proof of a causal relationship was not possible or intended. But because corresponding epidemiological studies are lacking, this documentation can give important information on characteristic features of Multiple Chemical Sensitivity Disorder and chronic neurotoxic health impairments. Such information is essential for planning and carrying out epidemiological studies urgently needed in this field.

Adolescent↗

PubMed1995

Magnetic orientation of spiny lobsters in the ocean: experiments with undersea coil systems

The western Atlantic spiny lobster Panulirus argus undergoes an annual migration and is also capable of homing to specific dens in its coral reef environment. Relatively little is known, however, about the orientation cues that lobsters use to guide their movements. To determine whether lobsters can orient to the earth's magnetic field, divers monitored the orientation of lobsters tethered inside magnetic coil systems submerged offshore in the Florida Keys, USA. Each coil could be used to reverse either the horizontal or vertical component of the earth's field. Tethered lobsters walking inside the coils often established and maintained consistent courses towards specific directions. After a lobster had established a course, it was exposed to one of three conditions: (1) a reversal of the horizontal component of the earth's field; (2) a reversal of the vertical component of the earth's field; or (3) no change in the ambient field (controls). Lobsters subjected to the horizontal field reversal deviated significantly from their initial courses. In contrast, control lobsters and those subjected to the reversed vertical field did not. These results demonstrate that spiny lobsters possess a magnetic compass sense. Because inverting the vertical component of the earth's field had no effect on orientation, the results suggest that the lobster compass is based on field polarity and thus differs from the inclination compasses of birds and sea turtles. The magnetic compass of lobsters may function in homing behavior, in guiding the autumn migration or in both.

Journal Article↗

PubMed1995

Evidence for hydrodynamic orientation by spiny lobsters in a patch reef environment

Western Atlantic spiny lobsters (Panulirus argus) are superb underwater navigators. Spiny lobsters perform dramatic seasonal offshore migrations and have also been shown to locate and home to specific den sites within the elaborate coral reef environment in which they live. How these animals perform such complex orientation tasks is not known. The study reported here was designed to explore the sensory mechanisms that spiny lobsters use to orient in and around a familiar patch reef environment. Our results show that, in the absence of visual cues, lobsters displaced a short (50 m) distance off the reef do not initially (i.e. within 20 min) travel towards their dens or return to the patch reef where their dens are located. Instead, the headings lobsters follow are significantly correlated to the direction of local hydrodynamic cues and, specifically, to the direction of approaching wave surge. Results from ultrasonic tracking experiments over longer periods (24 h) suggest that displaced lobsters are able to relocate the reef where they were captured, even without visual cues. These results suggest that hydrodynamic cues may provide useful and immediate directional information to lobsters within the local environment of the home reef.

Journal Article↗

PubMed1995

Perception of ocean wave direction by sea turtles

At the beginning of their offshore migration, hatchling sea turtles enter the ocean at night and establish a course away from land by swimming directly into oceanic waves. How turtles can detect wave direction while swimming under water in darkness, however, has not been explained. Objects in a water column beneath the surface of the ocean describe a circular movement as waves pass above. In principle, swimming turtles might, therefore, detect wave direction by monitoring the sequence of accelerations they experience under water. To determine whether loggerhead (Caretta caretta L.) and green turtle (Chelonia mydas L.) hatchlings can detect wave direction in this way, we constructed a wave motion simulator to reproduce in air the circular movements that occur beneath small ocean waves. Hatchlings suspended in air and subjected to movements that simulated waves approaching from their right sides attempted to turn right, whereas movements that simulated waves from the left elicited left-turning behavior. Movements simulating waves from directly in front of the turtles elicited little turning in either direction. The results demonstrate that hatchling sea turtles can determine the propagation direction of ocean waves by monitoring the circular movements that occur as waves pass above. Although sea turtles are the first animals shown to be capable of detecting wave direction in this way, such an orientation mechanism may be widespread among other transoceanic migrants such as fish and cetaceans.

Journal Article↗

PubMed1994

ACQUISITION OF MAGNETIC DIRECTIONAL PREFERENCE IN HATCHLING LOGGERHEAD SEA TURTLES

During their natal migration, hatchling loggerhead sea turtles (Caretta caretta L.) establish courses towards the open ocean and maintain them after swimming beyond sight of land. Laboratory experiments have demonstrated that swimming hatchlings can orient using the earth's magnetic field. For the magnetic compass to function in guiding the offshore migration, however, hatchlings must inherit or acquire a magnetic directional preference that reliably leads them towards the open sea. On land, hatchlings find the ocean using light cues associated with the seaward horizon. To determine whether turtles might acquire a preference for a specific magnetic direction on the basis of such cues, we studied the magnetic orientation of turtles initially exposed to light from either magnetic east or west. Hatchlings that had been exposed to light in the east subsequently oriented eastward when tested in darkness, whereas those that had been exposed to light in the west swam westward. Reversing the magnetic field resulted in a corresponding shift in orientation, indicating that the turtles were orienting to the ambient magnetic field. These results demonstrate that light cues can set the preferred direction of magnetic orientation by loggerhead hatchlings. We therefore hypothesize that hatchlings initially establish a seaward course using visual cues available on or near land, then maintain the course using magnetic cues as they migrate into the open sea.

Journal Article↗

PubMed1994

DETECTION OF MAGNETIC INCLINATION ANGLE BY SEA TURTLES: A POSSIBLE MECHANISM FOR DETERMINING LATITUDE

For animals that migrate long distances, the magnetic field of the earth provides not only a possible cue for compass orientation, but a potential source of world-wide positional information. At each location on the globe, the geomagnetic field lines intersect the earth's surface at a specific angle of inclination. Because inclination angles vary with latitude, an animal able to distinguish between different field inclinations might, in principle, determine its approximate latitude. Such an ability, however, has never been demonstrated in any animal. We studied the magnetic orientation behavior of hatchling loggerhead sea turtles (Caretta caretta L.) exposed to earth-strength magnetic fields of different inclinations. Hatchlings exposed to the natural field of their natal beach swam eastward, as they normally do during their offshore migration. In contrast, those subjected to an inclination angle found on the northern boundary of the North Atlantic gyre (their presumed migratory path) swam south-southwest. Hatchlings exposed to an inclination angle found near the southern boundary of the gyre swam in a northeasterly direction, and those exposed to inclination angles they do not normally encounter, or to a field inclination found well within the northern and southern extremes of the gyre, were not significantly oriented. These results demonstrate that sea turtles can distinguish between different magnetic inclination angles and perhaps derive from them an approximation of latitude. Most sea turtles nest on coastlines that are aligned approximately northsouth, so that each region of nesting beach has a unique inclination angle associated with it. We therefore hypothesize that the ability to recognize specific inclination angles may largely explain how adult sea turtles can identify their natal beaches after years at sea.

Journal Article↗

PubMed1989

[Behavior and pathogenicity of larva of Toxocara canis Werner 1782 (Anisakidae) in the mouse].

To evaluate the interdependence between pathological changes and the level of infection the behaviour of Toxocara canis larvae in the host, the course of the disease as well as quality and quantity of histological changes were investigated after experimental infection with 1,000, 500, 250, and 125 larvae respectively. The main places where the larvae of Toxocara canis were found at any time after infection were musculature and brain. Regardless of the level of infection the absolute and relative number of larvae in the brain increased linearly, and parallel decreased in musculature. After the 60th day post infection the mice infected with 1,000 larvae showed compulsive movements, disturbance of equilibrium and paralysis of the hindlegs. The mice infected with 500 larvae showed similar symptoms 30 to 40 days later. Mice with weaker infections only showed slight disturbances of the general condition at the end of the trials. In the brain of all animals infected with larvae of Toxocara canis inflammatory reactions were found. Severe destructive changes in the nervous substance together with clinical symptoms were seen only in higher infected mice.

Animals↗