Search PubMed⌕ Search

Biomedical subjects

A Kittel

Publications and source records attributed to A Kittel.

At least 37 records · Page 2Linked to original sources
PubMed1996

Qualitative enzyme histochemistry and microanalysis reveals changes in ultrastructural distribution of calcium and calcium-activated ATPases after microwave irradiation of the medial habenula.

The localization of calcium and calcium-activated ATPases was investigated electron microscopically in the medial habenula of mice after whole body irradiation with modulated microwaves. In non-irradiated animals calcium-containing precipitates were seen in different subcellular compartments and were often localized on the luminal side of membranes of synaptic vesicles in nerve terminals. At 1 h after 16-Hz modulated microwave irradiation, the number of synaptic vesicles containing calcium precipitates decreased, and reaction products appeared at new locations: in the synaptic clefts and on non-synaptic surfaces of the neuronal plasma membrane. This modified calcium distribution remained unchanged for 24 h following irradiation. Calcium-activated "ecto"-localized ATPase was detected as a punctuated-linear distribution of the reaction product outlining whole areas of glial and neuronal plasma membrane in the habenula of control animals. This pattern did not change on microwave irradiation. However, a quercetin-sensitive "endo"-localized Ca(2+)-ATPase activity appeared in some nerve terminals 24 h after irradiation. Thus, microwave irradiation can influence neuronal calcium homeostasis by inducing Ca2+ redistribution across the plasma membrane and by modifying Ca(2+)-ATPase activity. However, no direct correlation between these effects could be demonstrated by the present study.

Animals↗
PubMed1995

Early endocytotic steps in elicited macrophages: omega-shaped plasma membrane vesicles at their cell surface.

Fluid-phase and receptor-mediated endocytosis were studied in Freund's adjuvant elicited macrophages. These cells were found to bind and internalize significantly larger amounts of peroxidase-antiperoxidase (PAP) immune complex than resident macrophages. Similarly the rate of the fluid-phase uptake was higher in elicited cells. When studying the early steps of endocytotic processes, omega-shaped plasma membrane pits (d approximately 90 nm) were found at the macrophage cell surface. Although occurring occasionally in resident cells, their number was highly increased after elicitation in 30% of the macrophage cell population. The different morphology of these cells coincided with a lower endocytotic activity and a very strong ecto Ca(2+)-ATPase reaction. The present findings indicate that the elicited macrophage population is heterogenous and consists of different subclasses.

Animals↗
PubMed1995

A1-receptor-mediated effect of adenosine on the release of acetylcholine from the myenteric plexus: role and localization of ecto-ATPase and 5'-nucleotidase.

No attempt has been made so far to classify the subtypes of presynaptic inhibitory adenosine receptors located in the myenteric plexus and to localize ecto-ATPase and 5'-nucleotidase in the intestine. The release of [3H]acetylcholine and smooth muscle responses to acetylcholine were measured and the effect of selective adenosine receptor ligands was studied using field-stimulated isolated longitudinal muscle strips of guinea-pig ileum. Release of ATP and its hydrolysis rate were also measured using the luciferin-luciferase technique. A histochemical method combined with electron microscopy was used for localization of ecto-ATPase and 5'-nucleotidase, enzymes responsible for destruction of extracellular ATP, ADP and AMP. Subtype-selective A1-receptor agonists and antagonists inhibited and enhanced, respectively, the release of acetylcholine associated with neuronal activity. A significant amount of ATP was released in response to electrical stimulation and administration of carbamylcholine. The release of ATP was inhibited by atropine and 4-diphenylacetoxy-N-methylpiperidine methiodide, an M3-receptor antagonist. Hydrolysis of ATP was rapid and resulted in an accumulation of extracellular adenosine involved in presynaptic A1-receptor-mediated inhibition of acetylcholine release. While the inhibitory effect of adenosine and ATP was significantly potentiated by dipyridamol, an adenosine uptake blocker, that of 2-ms ATP was not. The effect of ATP was not competitively antagonized by 8-cyclopentyl-1,3-dipropylxanthine, a selective A1-receptor antagonist. In conclusion, axon terminals of cholinergic interneurons are equipped with inhibitory A1- and P2 gamma-receptors. Therefore, both adenosine and ATP control the release of acetylcholine through these receptors. ATP is mainly released from the smooth muscle in response to stimulation of M3-muscarinic receptors by endogenous acetylcholine (cascade transmission [Vizi E. S. et al. (1992) Neuroscience 50, 455-465]) and is rapidly hydrolysed by ecto-ATPase localized on the surface of the smooth muscle and axon terminals producing ADP and AMP, and by 5'-nucleotidase present only on the surface of smooth muscle cells producing adenosine.

5'-Nucleotidase↗
PubMed1995

ATP acts as fast neurotransmitter in rat habenula: neurochemical and enzymecytochemical evidence.

The release of ATP and ADP, the putative central neurotransmitters, from the isolated habenula preparation was investigated in the rat, at rest and during electrical stimulation, using the luciferin-luciferase assay and the creatine phosphokinase assay. Electrical field stimulation (2 Hz, 360 pulses) released a considerable amount of ATP (2450 +/- 280 pmol/g wet tissue) from the tissue; inhibition of the voltage Na+ entry by tetrodotoxin (1 microM) reduced significantly the evoked release (by 66.25 +/- 6.65%), but not the resting release of ATP. Endogenous ADP also appeared in the effluent, but its amount differed during resting condition and after stimulation from that of ATP, suggesting that the majority of the released compound is ATP in response to stimulation. When ATP was added to the tissue, it readily decomposed to ADP and AMP (Km = 811.6 +/- 68.88 microM, vmax = 23.1 +/- 2.75 nmol/min per prep., measured by high-performance liquid chromatography combined with ultraviolet detection), indicating that the habenula contains ectoATPases. In addition, the inactivation of extracellular ATP by the ectoATPase enzyme was also visualized by electron microscopic enzyme cytochemistry. The ectoATPase enzyme was present on the membranes of the dendrites and nerve terminals and in the synapses of the habenula. Taking into account the fact that ATP is ubiquitous in excitable cells (storage) and the findings published by Edwards et al. in 1992 ("ATP receptor-mediated synaptic currents in the central nervous system", Nature, Vol. 359, pp. 144-147), our data provides evidence for the release by axonal stimulation and extracellular decomposition of ATP, all needed for an endogenous substance qualified as a transmitter.

Adenosine Diphosphate↗
PubMed1995

The precursor protein of non-A beta component of Alzheimer's disease amyloid is a presynaptic protein of the central nervous system.

Non-A beta component of Alzheimer's disease amyloid (NAC) is the second component in the amyloid from brain tissue of patients affected with Alzheimer's disease. Its precursor protein (NACP) was shown to be a brain-specific protein. In rat brain, NACP was more abundant in the neocortex, hippocampus, olfactory bulb, striatum, thalamus, and cerebellum and less abundant in the brain stem. Confocal laser microscopy analysis revealed that anti-NACP immunostaining was colocalized with synaptophysin-immunoreactive presynaptic terminals. Ultrastructural analysis showed that NACP immunoreactivity was associated with synaptic vesicles. NACP sequence showed 95% identity with that of rat synuclein 1, a synaptic/nuclear protein previously identified in rat brain, and good homology with Torpedo synuclein from the electric organ synapse and bovine phosphoneuroprotein 14 (PNP-14), a brain-specific protein present in synapses. Therefore, NACP is a synaptic protein, suggesting that synaptic aberration observed in senile plaques might be involved in amyloidogenesis in Alzheimer's disease.

Alzheimer Disease↗
PubMed1995

Heterogeneous distribution of ecto-Ca-ATPases in primary cultures of human adenohypophyseal cells.

The aim of this study was to investigate the localization of ecto-Ca-adenosine-triphosphatase (ecto-Ca-ATPase) in different parenchymal cells of the human pituitary in tissue culture. The distribution of ecto-ATPases on the surface membrane of a particular parenchymal cell varied with the type of cells in contact with this parenchymal cell; the membrane portions immediately exposed to the medium showed low if any ecto-ATPase activity. These results suggest that ecto-Ca-ATPases of the parenchymal cells may be involved in cell adhesion processes and may be of crucial importance in the organization (in vivo) and reorganization (in vitro) of human adenohypophyseal tissue.

Adenosine Triphosphatases↗
PubMed1994

Ecto-ATPases and 5'-nucleotidases in the caveolae of smooth muscle. Enzyme-histochemical evidence may indicate a role for caveolae in neurotransmission.

We have demonstrated the localization of ecto-Ca-ATPase and 5'-nucleotidase activity in the caveolae of smooth muscle cells of guinea pig was deferens and the ileum longitudinal muscle strips with a cerium-precipitation enzyme-cytochemical method. The activities seemed to be strongest in the caveolae. Since the simultaneous presence of the 5'-nucleotidase activity supports the hypothesis that this ecto-Ca-ATPase activity does not have a pump function, but, together with 5'-nucleotidase, may play a role in neurotransmission, these specific membrane invaginations, the caveolae, have a functional relationship with transverse tubules of striated muscle.

5'-Nucleotidase↗
PubMed1994

Presynaptic ecto- and postsynaptic endo-calcium-adenosine-triphosphatases in synaptosomes: doubts about biochemical interpretation of localization.

Ecto- and endo-Ca-adenosine-triphosphatase (ATPase) activity was identified as electron-dense lead or cerium phosphate precipitate in the rat cortical synaptosomes by transmission electron microscopy and enzyme histochemistry. The formation of the deposit was dependent on the presence of ATP (the substrate), Ca (activator) and levamisole, quercetin or ouabain (inhibitors of different phosphatases and ATPases). Reaction products were found at the external surface of the presynaptic membrane, both surfaces of the postsynaptic membrane, in the synaptic cleft and in the free mitochondrial membranes. In the presence of ATP and the three inhibitors together, the quantity of the precipitate decreased markedly, but we still found some deposit on the external surface of the presynaptic membrane (this activity is probably due to the so-called ecto-ATPase) and on the internal surface of the postsynaptic one (endo-ATPase). The distinction between ecto- and endo-ATPases in biochemical fractions solely upon biochemical differential measurements must be interpreted with caution.

Animals↗
PubMed1994

Distribution of Ca-ATPases in the medial habenula in mouse.

The aim of this study was to investigate the distribution of the ecto-Ca,Mg-adenosine-triphosphatases (ecto-Ca,Mg-ATPases) in the medial habenular nucleus. Nerve terminals that seemed to be similar in morphological terms showed a different distribution of enzyme activity. Also, synapses showed a different distribution of enzyme activity. This could be related to the involvement of different neurotransmitters and modulators.

Animals↗
PubMed1986

Differential responses of synaptosomal cation movements and respiration to the convulsants penicillin, pentylenetetrazol and 3-aminopyridine.

The effect of three convulsants was tested in rat cortical synaptosomes by measuring Na+ and K+ movements and respiration. Penicillin (of its derivatives the 3-phenyl-5-methyl-4-isoxazolyl-penicillin, i.e. oxacillin was used) at 2 to 14 mM concentration prolonged the uptake phase of the K+-curve without altering final cation equilibrium. Pentylenetetrazol, at 10 to 50 mM exerted a concentration-dependent inhibitory effect on K+-uptake, while 3-aminopyridine was effective only at high concentrations (50 mM) preventing synaptosomal K+-uptake and increasing the synaptosomal Na+-content without, however, blocking respiration. The data suggest a transitional rise of K+-permeability of synaptosomal membrane in the presence of oxacillin, without lasting depolarization. Sufficient doses of 3-aminopyridine probably depolarize synaptosomes, the underlying mechanism probably being associated with the primary blocking of K+-channels and a subsequent increase in Na+ influx rather than with the inhibition of the Na+--K+-pump.

Aminopyridines↗
PubMed1985

Inhibition of lipid peroxidation by heme-nonapeptide derived from cytochrome c.

Heme-nonapeptide, derived from cytochrome c, inhibited both the NADPH- and NADH-dependent lipid peroxidation of brain microsomes but, in the case of liver microsomes, this inhibitory effect manifested itself in the presence of SKF-525A (a specific blocker of cytochrome P-450) only. Heme-nonapeptide prevented the transient accumulation of lipid peroxides in microsomes during lipid peroxidation. The oxygen consumption of microsomes in the presence of NADPH or NADH was stimulated by heme-nonapeptide. From these results we concluded that, in vitro, there are two independent mechanisms of lipid peroxidation in liver microsomes. It is suggested that, in vivo, the heme-peptide-sensitive mechanism, observed in brain microsomes, is more important.

Animals↗
PubMedDate not supplied

Home rehabilitation for older adults with fractured hips: how many will take part?

Rehabilitation at home is a new 'technology' which has been promoted as an efficient alternative to hospital rehabilitation for older patients with conditions such as fractured hip. In Australia, no formal description of elderly patients with fractured hips likely to be eligible for home rehabilitation has been made and the acceptability of such services is unclear. Using information obtained prospectively from a consecutive sample of 188 patients with a fractured hip we describe the characteristics of older adults who were eligible for a trial examining home versus hospital rehabilitation. While staff assessed 36% of patients as eligible, only 20% were both eligible and agreeable. Reasons for refusal to participate included a preference for inpatient rehabilitation (26%), family reluctance (26%) and anxiety regarding the ability to manage at home (16%). Our results suggest that home rehabilitation is suitable for the least disabled group but is still unacceptable to many elderly patients and their families. As the population ages and hip fractures increase, home rehabilitation in its current form will have little impact on future bed needs.

Aged↗