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D Hoppe

Publications and source records attributed to D Hoppe.

18 recordsLinked to original sources
PubMed1991

Characteristics of activity-dependent potassium accumulation in mammalian peripheral nerve in vitro.

Ion-sensitive microelectrodes were used to study the behavior of extracellular ions in rat sciatic nerve during and following activity. Nerve stimulation produced increases in [K+]o that were dependent upon the frequency and duration of stimulation; no change in extracellular pH occurred with stimulation. Increases in [K+]o depended on axonal discharge since they were blocked by inhibiting sodium channels with tetrodotoxin. At 22 degrees C, stimulation could induce increases in [K+]o of several mM; at 36 degrees C, stimulation rarely produced increases in [K+]o greater than 1 mM. Stimulated increases in [K+]o dissipated very slowly (i.e. t 1/2 = 50-100 s) and the rate of dissipation was not significantly affected by anoxia, changes in temperature, changes in extracellular pH, or the application of a blocker of Na+, K(+)-ATPase (ouabain) or a K+ channel blocker (Ba2+). In comparison to the central nervous system, neural activity in rat sciatic nerve produced smaller increases in [K+]o and these increases dissipated much more slowly. The primary mechanism of K+ dissipation appeared to be diffusion, probably facilitated by the larger extracellular space in peripheral nerve compared to the central nervous system, but impeded by diffusion barriers imposed by the blood-nerve barrier.

Action Potentials↗
PubMed1991

Single K+ channel properties in cultured mouse Schwann cells: conductance and kinetics.

Cultured Schwann cells are characterized by a strong outward rectification of the membrane; the threshold of the outward currents is close to the resting membrane potential of about -50 mV (Gray et al.: In Ritchie, Keynes (eds): Ion Channels in Neural Membranes. New York: Alan R. Liss, Inc., pp 145-157, 1986). These outward currents show up a heterogeneity among the cultured Schwann cells: some cells displayed inactivating, others non-inactivating outward currents (Hoppe et al.: Pflügers Arch 415:22-28, 1989). In this study we characterized the single channel currents using the patch-clamp technique in the intact patch recording configuration. The conductance of all recorded channels was 10-12 pS (5.6 mM [K+]o). These channels were K+ selective since changes in extracellular [K+] resulted in changes of the reversal potential as predicted for an exclusively K+ selective pore. The reversal potentials also predicted an intracellular [K+] of 60 mM indicating that the K+ equilibrium potential is slightly negative to the membrane potential. Analysis of the kinetic behavior of the channels resolved two different types of behaviour: 40% inactivated during a depolarizing voltage step, the others showing no sign of inactivation. The analysis of open probability and gating properties in the steady state showed up more differences between these two channel types: mean open probability peaked at about 10 mV for inactivating channels, while it continuously increased for non-inactivating channels. The inactivation time constants of averaged single channel and whole cell currents were similar and showed both a similar voltage dependency. We conclude that cultured Schwann cells express either two types of K+ channels with similar conductance or a channel which can acquire two functional states and that these channels can account for the different types of K+ currents observed in these cells.

Animals↗
PubMed1991

K+ channel properties in cultured mouse Schwann cells: dependence on extracellular K+.

In cultured Schwann cells, single-channel and whole-cell K+ currents can be activated by depolarizing the membrane to values more negative than -50 mV. In elevated extracellular K+ concentration ([K+]o), however, single-channel activity and whole-cell currents could be recorded at more negative potentials. Thus, the threshold of current activation was shifted to more negative potentials. This shift in the activation threshold was only observed with normal (50-60 mM) intracellular [K+] levels; it was not apparent when [K+]i was elevated to 145 mM. The control of [K+]o on the gating properties of K+ channels may serve to enhance the capability of the Schwann cell to take up [K+]o and thus may serve for [K+] homeostasis in the peripheral nerve.

Animals↗
PubMed1991

A subpopulation of bone marrow-derived macrophage-like cells shares a unique ion channel pattern with microglia.

Rat microglia share a number of antigenic, functional, and morphological similarities with macrophages from other tissues, but are characterized by a distinctly different pattern of ion channels in the cellular membrane (Kettenmann et al., J Neurosci Res 26:278-287, 1990). Macrophages typically express outward and inward K+ currents. In contrast, microglia lack outward currents and only show inwardly rectifying K+ currents, regardless of the isolation or cultivation method employed for microglia. In this study we demonstrate that a subpopulation of bone marrow-derived macrophage-like cells possesses inward rectifier K+ currents, but no outward currents and thus with regard to the electrophysiological characteristics closely resembles microglia. A second population of bone marrow-derived macrophage-like cells shows the usual channel pattern described for other body macrophages. Our results strengthen the hypothesis that in the bone marrow distinct pools of precursor cells exist, possibly reflecting an early differential lineage determination for body and brain macrophages, i.e., microglia.

Animals↗
PubMed1991

Two populations of glial cells from fish optic nerve/tract with distinct electrophysiological properties.

The electrophysiological properties of the two major glial cell types in cultures from the regenerating goldfish optic nerve/tract were studied with patch-clamp techniques. Spindle-shaped cells express myelin proteins. These oligodendrocyte-like cells possess outwardly rectifying currents, do not show glutamate activated currents and are rarely electrically coupled to neighboring cells. Cells of epitheloid morphology probably represent astrocytes. They are GFAP-positive and do not exhibit myelin proteins. These cells have glutamate activated currents, display a linear current to voltage relationship and are extensively electrically coupled thus displaying properties similar to mammalian astrocytes.

4-Aminopyridine↗
PubMed1990

Cultured microglial cells have a distinct pattern of membrane channels different from peritoneal macrophages.

Microglia are the source of the resident macrophages of the brain and thus belong to one of the most reactive cell types in cerebral tissue. They are attributed to have an important role in a number of pathological conditions, such as multiple sclerosis, viral infections like AIDS, and in lethal or sublethal injuries of neurons where the blood-brain barrier is left intact (Streit et al., 1988; McGeer et al., 1988; Gendelman et al., 1989). Microglia share a number of macrophage characteristics but so far lack a distinguishing positive marker. In this study it is shown that microglia are distinguished from other macrophages by a unique pattern of ion channels. We compared membrane currents of microglial cells with those from peritoneal macrophages cultured under identical conditions. Although in macrophages a delayed outward K+ current was previously described (Randriamampita and Trautmann, 1987), microglial cells lacked any specific outward current. Instead, these cells were characterized by large inwardly rectifying currents, activated by hyperpolarizing voltage steps. The reversal potential in different K+ gradients and the sensitivity of the current to to Ba2+, TEA, and 4-AP indicates that this current is K+ selective. In single-channel recordings, a 30 pS K+ selective channel similar to the classical inward rectifier K+ channel was observed. Thus, the expression of membrane channels served not only to distinguish microglia from other cells inside and outside the brain, e.g., blood macrophages, but also suggests a unique functional state of this cell population.

Animals↗
PubMed1989

GABA triggers a Cl- efflux from cultured mouse oligodendrocytes.

gamma-Aminobutyric acid (GABA) has been shown to depolarize the membranes of astrocytes and oligodendrocytes taken from different tissues and species. The mechanism mediating this depolarization was identified, in cultured rat brain astrocytes, as an activation of GABA receptor-linked Cl- channels. A subpopulation of cultured oligodendrocytes from mouse spinal cord also responded to GABA with a membrane depolarization. In the present study we demonstrate that, in oligodendrocytes, the depolarization was accompanied by a decrease in intracellular Cl- activity [( Cl-]i) as measured with ion-selective microelectrodes. At rest, [Cl-]i was elevated above the passive distribution, and upon application of GABA, [Cl-]i decreased towards the level of passive distribution. Furosemide blocked the Cl- inward carrier which led to a passive Cl- distribution; in the presence of furosemide, GABA no longer elicited a membrane depolarization or a change in [Cl-]i. We conclude that oligodendrocytes, which were depolarized by GABA, expressed GABA-activated Cl- channels. Oligodendrocytes which were unresponsive to GABA demonstrated a non-passive Cl- distribution indicating that they did express inward-directed Cl- carriers, but no GABA-activated Cl- channels.

Animals↗
PubMed1989

Carrier-mediated Cl- transport in cultured mouse oligodendrocytes.

We studied the steady state and the regulation of intracellular Cl- activity (aCl-i) and the mechanisms of KCl uptake in cultured oligodendrocytes from mouse spinal cord using Cl(-)-selective microelectrodes. The majority of oligodendrocytes actively accumulated Cl- above passive distribution (2-3 mM), few cells showed a passive Cl- distribution. To identify the carriers mediating Cl- uptake, oligodendrocytes were maintained in a solution with low extracellular Cl- concentration ([Cl-]o) which resulted in a rapid decrease in aCl-i. The recovery of aCl-i above its passive distribution in normal [Cl-]o was blocked in the absence of Na+ or in the presence of furosemide and of bumetanide, which has been reported to inhibit Na+/K+/Cl- cotransport. We therefore conclude that Cl- uptake is primarily due to the activity of a Na+K+/Cl- transport system. Cl- uptake above passive distribution was not affected in HCO3(-)-free solution or in the presence of SITS and DIDS, indicating that Cl-/HCO3- exchange is not involved in Cl- uptake by oligodendrocytes. Elevation of [K+]o induced an increase in aCl-i and, as shown earlier, intracellular K+ activity. This K+-induced Cl- uptake was not blocked by bumetanide, furosemide, SITS, or DIDS, suggesting that under conditions of raised [K+]o the combined uptake of K+ and Cl- is not mediated by a carrier, but can be explained by the entry through channels driven by Donnan forces.

Animals↗
PubMed1989

Glial cells of the oligodendrocyte lineage express proton-activated Na+ channels.

Neurons and oligodendrocytes, but not type I astrocytes and Schwann cells, generate large Na+ currents in response to a step increase of [H+]. Proton-activated Na+ channels are the first cationic channels expressed in neuronal precursor cells from the mammalian brain. Glial precursor cells cultured from mouse brain are also capable of generating Na+ currents in response to step acidification (INa(H]. With further development along the oligodendrocyte lineage, this property is retained, whereas voltage-activated Na+ and K+ currents disappear. Comparing INa(H) of oligodendrocytes with INa(H) of their precursor cells did not reveal a difference in current amplitude, suggesting a higher density of INa(H) channels on the (smaller) precursor cells. The properties of INa(H) in glial precursor cells and oligodendrocytes are similar to those of neurons, with respect to activation conditions, time course, and the effect of extracellular Ca2+ concentrations. The results are consistent with previous observations which showed that oligodendrocytes partially preserve their chemically activated, but completely lose their voltage-activated, ion channels.

Animals↗
PubMed1989

Activation of K+ currents in cultured Schwann cells is controlled by extracellular pH.

We analyzed the pH dependence of K+ currents recorded with the patch-clamp technique from cultured Schwann cells obtained from mouse dorsal root ganglia. Currents were activated at potentials more positive than -50 mV which was close to the resting membrane potential. Current amplitudes were affected by a change in extracellular pH (pHo), being increased at alkaline, and decreased at acidic pHo. The strongest effect of a pHo change was observed on currents activated close to the resting membrane potential suggesting a functional role for the pH sensitivity of K+ currents. Analysis of the time course of current activation at different pHo values led to the conclusion that the pH-sensitivity of K+ currents in Schwann cells is due to changes in surface charges shifting the potential sensed by the gating process of the channel. The reversal potential of the currents was not affected by a change in pHo. This observation and the finding that even a strong acidification to a pHo value of 5.0 did not lead to a blockade of the fully activated channel, indicate that the pH-sensitive charges are not located in the channel pore. Under the assumption that pHo changes in a peripheral nerve are associated with nerve activity as in the optic nerve, the pH-sensitive K+ channel in Schwann cells could serve to facilitate the spatial buffering of extracellular K+.

4-Aminopyridine↗
PubMed1989

Salivary gland myoepithelioma variants. Histological, ultrastructural, and immunocytological features.

The histological and ultrastructural features of five major salivary gland tumours, which have little or no evidence of duct- or gland-type differentiation in routine sections, are described. Four of the cases have the tumour cells organized as narrow, anastomosing cords of cells separated by a myxoid and vascularized stroma; we have designated such lesions as reticular-type myoepitheliomas. The fifth case has a solid growth pattern and is largely composed of hyaline cells, that is, a plasmacytoid myoepithelioma. Ultrastructurally, one reticular myoepithelioma reveals myoepithelial cell differentiation with microfilament aggregates, while the other three examples are composed of modified myoepithelial cells displaying widened intercellular spaces, prominent synthesis of extracellular glycosaminoglycans, distinct basal lamina development, and obvious accumulations of cytoplasmic intermediate filaments. In electron micrographs, the modified myoepithelial cells of the plasmacytoid variant closely resemble the tumour cells in the reticular form. Three cases had expression of both glial fibrillary acid protein (GFAP) and vimentin, but only one of the myoepitheliomas contained muscle-specific actin. At least focally, each of the cases exhibited a considerable spectrum of cytokeratin filaments. Using double-labeled immunofluorescent microscopy of one reticular variant and the plasmacytoid myoepithelioma, there was individual tumour cell co-expression of GFAP and vimentin focally in the plasmacytoid myoepithelioma, but co-expression of cytokeratins 13, 16 and GFAP were not noted in either case. As expected, co-expression of high- and low-molecular weight cytokeratin filaments was widespread in both myoepitheliomas. Most described myoepitheliomas have a solid growth pattern and are composed of spindle and plasmacytoid cells, but based on cytological features and growth patterns in this series, it is apparent that polygonal-shaped cells with novel architecture can occur in myoepitheliomas. The results also indicate the close relationship between pleomorphic adenoma and such variants of myoepithelioma.

Actins↗
PubMed1988

Warthin's tumor: an ultrastructural and immunohistochemical study of basilar epithelium.

The cellular characteristics of the basilar epithelium in Warthin's tumor have had limited investigation. Ultrastructural examination of basal cells in 9 Warthin's tumors reveals that in addition to numerous mitochondria these cells possess a rich complement of tonofilaments. However, in three examples there are a proportion of these tonofilament-rich cells that have a narrow band of microfilaments in the peripheral cytoplasm adjacent to the basal lamina. Frozen sections of Warthin's tumor and normal salivary glands, doubly labeled with rhodamine-phalloidin for actin and monoclonal antibody 312C8-1 for cytokeratin 14, show that normal myoepithelial cells of acini and intercalated ducts have both of these filaments, as do a proportion of basal cells in the tumor. There are distinct differences in the cytokeratin polypeptide complement between normal luminal and myoepithelial cells as well as between luminal and basal cells in Warthin's tumor. Differences occur in the cytokeratin profiles between the luminal and basal cells of Warthin's tumor and comparable cells in the normal gland; however, there continue to be some similarities in the cytokeratin polypeptides of myoepithelium and the basal cells of normal salivary ducts and the basal cells of Warthin's tumor. These findings show that basal cells in Warthin's tumor are a mixed population with some capable of differentiating as myoepithelial-like cells, and that this tumor could arise from any level of the normal salivary gland duct system.

Adenolymphoma↗
PubMed1988

CAPD in elderly patients with cardiovascular risk factors.

Twenty-nine elderly patients (greater than 70 years) on CAPD treatment were compared with 30 younger patients (less than 55 years). Biochemical parameters did not differ between the two groups, apart from blood sugar which was higher in the older patient group. Ultrafiltration rates were almost identical. CAPD-specific complications also did not differ in the two patient groups. Arterial hypertension was well-controlled on CAPD and the proportion of patients requiring antihypertensives fell significantly. 8% of the old patients and 52% of the young patients required antihypertensive medication after 12 months of therapy compared to 38% and 81% before commencement of CAPD. Improvement of hemodynamic parameters was especially pronounced in older patients, who had cardiac risk factors in a high percentage of cases. Age and cardiac risk factors had the highest impact on the outcome, thus explaining the higher mortality in the older patient group. Older patients with renal insufficiency can be treated with CAPD leading to equally good results as those documented for younger patients.

Actuarial Analysis↗
PubMedDate not supplied

Characterization of epimyoepithelial islands in benign lymphoepithelial lesions of major salivary gland: an immunohistochemical and ultrastructural study.

Knowledge of the processes leading to the development of epimyoepithelial islands bears on histogenetic and morphogentic processes in salivary gland tumors. Immunohistochemical and ultrastructural investigations of the cellular composition of epimyoepithelial islands were carried out on three examples of benign lymphoepithelial lesions with varying histologic features. The monoclonal anti-keratin antibody 312C8-1, which specifically decorates myoepithelial cells of the normal salivary gland, also stains the myoepithelial cells surrounding residual acini and intercalated ducts in benign lymphoepithelial lesions and the cell population of epimyoepithelial islands, with the exception of persisting luminal epithelial cells. Ultrastructurally, the myoepithelial cells of involuting acini and ducts and the modified myoepithelial cells of epimyoepithelial islands, identified in both locations by the monoclonal antibody 312C8-1, show an increasing complement of tonofilament bundles. In addition, persisting lumens (often distended with lymphocytes) and definite luminal epithelial cells can be seen in electron micrographs of some epimyoepithelial islands. The designation for this characteristic epithelial feature of benign lymphoepithelial lesions is therefore appropriate.

Humans↗