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Biomedical subjects

A Liepins

Publications and source records attributed to A Liepins.

36 records · Page 2Linked to original sources
PubMed1991

Pneumonitis associated with coinfection by human herpesvirus 6 and Legionella in an immunocompetent adult.

The authors report a case of pneumonitis in a young healthy man caused by coinfection with human herpesvirus 6 (HHV-6) and Legionella pneumophila. The patient's course was complicated by severe respiratory, renal, hepatic, and central nervous system dysfunctions, which were believed to be primarily the results of his Legionella infection. Aggressive antibiotic treatment produced no response, and Legionella remained isolatable from lung tissue throughout several weeks of antimicrobial therapy. Human herpesvirus 6 was isolated from a sample of peripheral blood during the acute stage of the patient's illness, and numerous HHV-6--infected macrophages and lymphocytes were detected by immunohistochemical staining of biopsy-derived lung tissue. Paradoxically treatment of the patient with high-dose corticosteroids resulted in dramatic improvement of his condition, including clearance of the Legionella infection. The demonstration that corticosteroids efficiently inhibit HHV-6 replication in vitro suggests that the virus may have contributed to the patient's pneumonitis by enhancing tissue inflammation, by compromising the function of pulmonary macrophages, and, perhaps, by destroying the patient's CD4+ T lymphocytes. Human herpesvirus 6 may be able to function as a synergistic cofactor in lung infections by Legionella and other pathogens.

Adrenal Cortex Hormones↗
PubMed1990

Effects of deuterium oxide (D2O) on the development of hypertension and Ca2+ homeostasis in spontaneously hypertensive rats.

Increased calcium uptake in vascular tissues, leading to elevated cytosolic free calcium, has been implicated in the pathophysiology of hypertension. In this study we investigated the in vitro effect of deuterium oxide (D2O) on calcium uptake in Sprague-Dawley (SD) rat aortae as well as the effects of 25% D2O, orally administered to spontaneously hypertensive and Wistar-Kyoto (WKY) rats, on systolic blood pressure and aortic calcium uptake. The high calcium uptake induced by phenylephrine (50 mumols/l) via receptor-operated channels and by KCl (80 mmol/l) via voltage-operated channels in SD rat aortae was effectively reduced by D2O in a concentration-dependent manner. These results suggest that D2O, acting like a calcium channel blocker, effectively normalized vascular calcium uptake mechanisms. When, at 7 weeks of age, spontaneously hypertensive rats were given 25% D2O in their drinking water for a period of 6 weeks, the development of high systolic blood pressures and the associated increases in aortic calcium uptake were effectively prevented. D2O treatment did not affect blood pressures in normotensive WKY rats. The parallel increases in systolic blood pressure and in vascular calcium uptake suggest that increased calcium uptake mechanisms are associated with hypertension. Furthermore, D2O appears to prevent hypertension by normalizing calcium uptake in vascular smooth muscle.

Administration, Oral↗
PubMed1990

Deuterium oxide reduces agonist and depolarization-induced contraction of rat aortic rings.

The influence of deuterium oxide (D2O) on calcium-dependent vascular smooth muscle contraction was investigated. The effect of D2O on receptor-operated calcium channels was investigated with phenylephrine-induced contraction in the rat aortic ring preparation. D2O depressed the contraction response in a dose-dependent manner with 50% inhibition of maximum contraction observed with 60% D2O. The effect of 60% D2O on phenylephrine-induced contraction was reversible and not dependent on an intact endothelium. Sixty percent D2O also reduced potassium chloride induced contractions by 50%, indicating an effect on voltage-operated calcium channels. Studies with Bay K 8644, and L-type calcium channel activator, confirm an effect on utilization of extracellular calcium sources and on the voltage-operated calcium channel. Sixty percent D2O also depressed a calcium contraction dose-response curve by approximately 25%. Likewise, a change in the pD2' for nifedipine in the presence of D2O may indicate an effect on the nifedipine binding site and (or) the voltage-dependent calcium channel. Further studies were performed to determine whether the D2O effects were nonspecific or selective effects on the receptor- and voltage-operated calcium channels. Sucrose-induced contaction in the presence of 60% D2O was found to be inhibited by approximately 50%. D2O similarly affected isoprenaline relaxation, which would suggest a nonspecific D2O effect on the vascular smooth muscle contractile process.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1990

Kinetic analysis of K+ ion channel function in lymphokine-activated killer (LAK) cells.

K+ ion channels of lymphocytes have been implicated in cellular differentiation, activation and cytolytic functions. We previously demonstrated that K+ channel blockers modulate lytic activity of CTLs and LAK cells. In the present study, we define and quantitate the inhibitory effects of ion channel blockers on the lytic process using kinetic analysis of lysis. The K+ channel blocker, 4-aminopyridine, the neuroendocrine monoamine, serotonin, its agonist, quipazine, and the Ca++ dependent K+ channel blocker, quinidine were found to non-competitively inhibit the lytic process in a dose-dependent manner. These compounds inhibit lytic activity by causing a decrease in the maximum velocity (Vmax) by which LAK cells lyse tumor targets. These ion channel blockers did not alter effector or target cell viability or the binding of LAK cells to tumor cells. The inhibitory effects occurred at the effector cell level, since preincubation of LAK effector cells resulted in a dose-dependent decrease in Vmax which was related to a slower rate of target cell lytic programming (k2) by the LAK effector cells. Modulation of LAK cell lytic function occurs at a post-binding step, perhaps in the generation or release of the lytic signal.

4-Aminopyridine↗
PubMed1989

Serotonin modulated Ca++ dependent K+ channels in alloimmune effector cell lytic function.

Potassium channel activity has been implicated in the lytic function of cloned murine effector T lymphocytes (5) and human NK cells (12) as well as in the initiation of the injury process in tumor cells (23). In the present studies, the effects of various K+ channel blockers on the cytolytic function of in vivo derived alloimmune lymphocytes towards P815 tumor cells were evaluated. The classical K+ channel blocker 4-aminopyridine (4-AP), the naturally occurring monoamine serotonin (5-hydroxytryptamine, 5-HT) and its agonist, quipazine, as well as the Ca++ dependent K+ channel blocker quinidine were chosen for investigation based on their known ion channel gating properties. These agents, when present in the assay medium, inhibited in a dose dependent manner the lysis of P815 tumor cells as measured by specific 51Cr release. Preincubation of effector lymphocytes with the various K+ channel blockers resulted in greater inhibition of lysis than did the preincubation of target cells. The 5-HT agonist quipazine was of particular interest in that it inhibited the lytic process with equal effectiveness when continuously present in the assay medium or when the effector cells alone were preincubated. Quinidine was used to investigate whether Ca++ dependent K+ channels were the predominant ion channel involved in the lytic process. When present during the lytic assay, quinidine was similar to quipazine in terms of their dose range at which they inhibited the lytic process. These results indicate that 5-HT sensitive Ca++ dependent K+ channels are likely to be involved in the delivery of lytic signal(s) by immune effector lymphocytes and suggests that neuroendocrine products may modulate the functional activity of in vivo derived lymphocytes.

4-Aminopyridine↗
PubMed1989

Morphological, physiological and biochemical parameters associated with cell injury: a review.

Various forms of cellular injury, whether induced by immune effector cells, aberrant metabolic processes, chemotherapeutic drugs or temperature shifts, result in common morphological changes consisting of the formation and shedding of membrane vesicles from the injured cell surfaces. This dynamic cell surface membrane behavior appears to be dependent on the disruption of cytoplasmic microtubules. Concomitant with the altered cell surface morphology certain physiological and biochemical events have been found to be associated with cell injury. These include changes in membrane permeability, elevated oxygen consumption rates and nuclear DNA fragmentation. However, it remains to be experimentally established which of these biological changes defines a state of irreparable cell injury. The objective of the present review is to compare and evaluate the cell injury process induced by effector lymphocytes with that caused by low temperature. The latter mimics most, if not all, the currently known criteria of immune effector cell mediated injury of target tumor cells.

Animals↗
PubMed1989

Role of K+ ion channels in lymphokine-activated killer (LAK) cell lytic function.

Cells of the immune system possess K+ ion channels which have been implicated in various cellular functions including activation, differentiation and cytolytic function. To define the role of K+ ion channels in the lytic function of lymphokine-activated killer (LAK) cells, we investigated the effects of K+ channel blockers on their cytolytic activity. Results show that when LAK cell mediated cytolysis of AKIL-20 tumor cells was carried out in the presence of: a) the K+ channel blocker, 4-aminopyridine (4-AP); b) the monoamine, serotonin (5-hydroxytryptamine; 5-HT); c) the serotonin agonist, quipazine; d) or the Ca++ dependent K+ channel blocker, quinidine, the cytolytic activity of the LAK cells was inhibited in a dose-dependent manner. Preincubation of LAK effector cells also inhibited lysis in a dose-dependent manner, whereas preincubation of the AKIL-20 tumor target cells produced no inhibitory effects. This study demonstrates that K+ ion channels are involved in the LAK cell cytolytic process and that compounds, including neuroendocrine products, which modulate K+ ion channel function are capable of modulating the lytic activity of these effector cells.

4-Aminopyridine↗
PubMed1987

A possible role for K+ channels in tumor cell injury. Membrane vesicle shedding and nuclear DNA fragmentation.

Mastocytoma P815 tumor cells subjected to low temperature (O degrees C/l h) and shifted to 22 degrees or 37 degrees C undergo morphological, physiological and biochemical changes which are analogous to those induced by immune effector cells, i.e., changes in cell-surface morphology and membrane permeability, elevated O2 consumption rates and nuclear DNA fragmentation [18-21]. Utilizing this low-temperature shift method for the induction of cell injury, we investigated the possible role of K+ channels in this process. Results show that the two classical K+ channel blockers, tetraethylammonium (TEA) and 4-aminopyridine (4-AP), inhibited the low temperature-induced cell-surface membrane vesicle shedding as well as the nuclear DNA-fragmentation process. These results indicate that K+ channel function is required for tumor-cell injury as manifested by nuclear DNA fragmentation and cell-surface membrane vesicle (MV) shedding.

4-Aminopyridine↗
PubMed1985

Low temperature-induced cell surface membrane vesicle shedding is associated with DNA fragmentation.

Temperature shift conditions of 0 degree to 22 degrees C or 0 degree to 37 degrees C induce the formation and shedding of membrane vesicles (MV) from P815 tumor cell surfaces. When the MV shedding process takes place at 22 degrees C it occurs without changes in cell surface membrane permeability, whereas at 37 degrees C, changes in permeability to 51Cr and trypan blue do occur, thus mimicking the lymphocyte-mediated lytic process of tumor cells [1]. The present studies demonstrate that nuclear DNA fragmentation also occurs in both 0 degree to 22 degrees C and 0 degree to 37 degrees C temperature shifts but cell surface membrane permeability to DNA fragments occurs only in the latter condition, i.e., 0 degree to 37 degrees C. The microtubule-stabilizing agent deuterium oxide (D2O) inhibited the MV shedding process, the changes in membrane permeability, and DNA fragmentation. When P815 cells which had been induced to shed MV by the 0 degree to 22 degrees C temperature shift were labeled with 51Cr and used as targets for alloimmune lymphocytes, they were found to be as susceptible to T-cell lysis as control P815 cells. This result indicates that the lytic effect of alloimmune T lymphocytes can be exerted at the target cell surface membrane level independently of nuclear DNA fragmentation.

Animals↗
PubMed1985

Oxygen consumption by tumor cells during membrane vesicle shedding.

The incubation of mastocytoma P815 cells at low temperature (0 degrees C/1-2 hr), with a subsequent shift to greater than or equal to 20 degrees C results in the formation and shedding of membrane vesicles from the tumor cell surfaces. This process, when occurring at physiologic temperature (37 degrees C), mimics the morphological and membrane permeability changes occurring during T-lymphocyte mediated cytolysis of tumor cells. The latter is an oxygen dependent event, but it is not known whether this requirement is at the effector T cell or at the tumor cell level. The present study investigated the oxygen consumption rates of mastocytoma P815 cells induced to shed membrane vesicles by a temperature shift (0 degrees C/1-2 hrs----greater than or equal to 20 degrees C). Results showed that cells undergoing the membrane vesicle shedding process had significantly higher oxygen requirements than control non-shedding cells. Inhibition of the shedding process with deuterium oxide and hexylene glycol, reduced the oxygen consumption rates of low temperature treated cells to the level of control cells. The oxygen consumption rates of the latter were unaffected by these microtubule stabilizing agents. These data indicate that the oxygen required for immune T-cell mediated lysis of tumor cells may be at the target tumor cell level.

Animals↗
PubMed1984

Migration patterns and functional activity of cloned cytotoxic T lymphocytes in syngeneic and allogeneic mice.

The quantitative distribution of cytolytic T lymphocytes (CTL) generated in mixed leukocyte culture (MLC) and an interleukin-2 (IL-2)-dependent, CTL clone (WRL-A3) was investigated in various tissues of irradiated syngeneic and allogeneic mice. In addition, the ability of the WRL-A3 CTL clone to remain viable and retain antigen specificity following in vivo passage was evaluated. Injection i.v. of 51Cr-labeled cultured CTL resulted in: (1) extensive deposition of cells in the lungs with significantly more lymphocytes being recovered in allogeneic as compared with syngeneic lung tissue; (2) minimal accumulation in spleen with more in syngeneic than in allogeneic tissue; and (3) no localization in blood, femurs, thymus, or lymph nodes. The migration rate of cultured CTL exiting the lung during the first 4 hr was markedly faster in syngeneic than in allogeneic recipients and was directly associated with the distribution of these cells in other tissues at 24 hr. The WRL-A3 CTL clone recovered from irradiated syngeneic and allogeneic lung tissue at 1, 3, 6, 8, and 13 days after i.v. injection remained viable, even though no exogenous IL-2 was administered to the recipient mice. The recovered cells proliferated when recultured with IL-2, and retained their antigen specificity for Qed-1b target cells after in vivo passage. These findings indicate that restricted and undesirable tissue distribution, rather than impaired viability or loss of antigenic specificity, is the major obstacle to successful use of cultured CTL for adoptive immunotherapy of disseminated cancer.

Animals↗
PubMed1983

Possible role of microtubules in tumor cell surface membrane shedding, permeability, and lympholysis.

Low temperature (0 degrees C/1 hr) induced changes in the mastocytoma P815 cell surface morphology which mimicked those induced by alloimmune T-lymphocytes during the cytolytic process. These morphological changes consist of the formation and shedding of membrane vesicles (MV) from the P815 cell surface. When the low-temperature-induced MV shedding process takes place at 22 degrees C, it occurs without changes in membrane permeability to 51Cr, whereas at 37 degrees C, the kinetics of 51Cr release resemble those induced by alloimmune T lymphocytes. The effects of two microtubule-stabilizing agents, deuterium oxide and hexylene glycol, were investigated on the low-temperature-induced MV shedding process as well as on the lymphocyte-mediated cytolysis (LMC) of target cells. These agents were found to inhibit (a) the low-temperature-induced MV shedding, (b) the low-temperature-induced membrane permeability changes to 51Cr, and (c) the LMC process. These data indicate that disruption of microtubules may be involved in all these events.

Animals↗
PubMed1981

Shedding of tumor cell surface membranes.

Mastocytoma P815 cells are induced to form and shed membrane vesicles (MV) from their surfaces by incubation at low temperature (4 degrees C) for 1 hr. and subsequently allowing them to warm up to room temperature (22 degrees C). Within 1-2 hrs. at room temperature, up to 90% of the P815 cells form and shed MV from their surfaces. Both cells and vesicles remain trypan blue-excluding during the MV shedding process. This process is energy dependent in that it can be inhibited by 2-deoxyglucose, sodium azide and 2-4-dinitrophenol. The shed MV can be harvested by centrifugation on a 6% Ficoll cushion and quantitated in terms of protein content. The shedding of membrane vesicles from the tumor cell surfaces results in a significant reduction in the cell size.

Animals↗
PubMedDate not supplied

Nuclear pore complex ion channels (review).

It is currently thought that nuclear pore complexes (NPCs) primarily govern nucleocytoplasmic interactions via selective recognition and active transport of macromolecules. However, in various nuclear preparations, patch-clamp and fluorescence, luminiscence and ion microscopy support classical microelectrode measurements indicating that monoatomic ion flow across the nuclear envelope (NE) is strictly regulated. Gating of large conductance nuclear envelope ion channels (NICs) somewhat resembles that of gap junctional channels. In other respects, NICs are distinct in that they require cytosolic factors, are blocked by wheat germ agglutinin and are blocked and/or modified by antibodies to epitopes of NPC glycoproteins. Therefore, NIC activity, recorded as electrical current/conductance is likely to be intrinsic to NPCs. This observation suggests a potential use for the patch-clamp technique in establishing the mechanisms underlying nuclear pore gating in response to cytosolic and nucleosolic factors such as transcription and growth factors, oncogene and proto-oncogene products and receptors for retinoids, steroids and thyroid hormone. NIC activity may also be useful in evaluating the mechanisms of nuclear import of foreign nucleic acid material such as that contained in virons and viroids. Finally, in consideration to the electrophysiological data accumulated so far, the study of nuclear pore ion channel activity may help our understanding of other important issues such as cell suicide, programmed cell death or apoptosis.

Animals↗