Connexin-43 hemichannels opened by metabolic inhibition

The cause of altered ionic homeostasis leading to cell death during ischemia and metabolic inhibition is unclear. Hemichannels, which are precursors to gap junctions, are nonselective ion channels that are permeable to molecules of less than Mr 1000. We show that hemichannels open upon exposure to calcium-free solutions when they are either heterologously overexpressed in HEK293 cells or endogenously expressed in cardiac ventricular myocytes. In the presence of normal extracellular calcium, hemichannels open during metabolic inhibition. During ischemia and other forms of metabolic inhibition, activation of relatively few hemichannels will seriously compromise the cell's ability to maintain ionic homeostasis, which is an essential step promoting cell death.

State-dependent cocaine block of sodium channel isoforms, chimeras, and channels coexpressed with the beta1 subunit

Cocaine block of human cardiac (hH1) and rat skeletal (mu1) muscle sodium channels was examined under whole-cell voltage clamp in transiently transfected HEK293t cells. Low affinity block of resting mu1 and hH1 channels at -180 mV was the same, and high affinity block of inactivated channels at -70 mV was the same. Cocaine block of hH1 channels was greater than block of mu1 channels at voltages between -120 mV and -90 mV, suggesting that greater steady-state inactivation of hH1 channels in this voltage range makes them more susceptible to cocaine block. We induced shifts in the voltage dependence of steady-state inactivation at mu1 and hH1 channels by constructing mu1/hH1 channel chimeras or by coexpressing the wild-type channels with the rat brain beta1 subunit. In contrast to several previous reports, coexpression of the rat brain beta1 subunit with mu1 or hH1 produced large positive shifts in steady-state inactivation. Shifts in the voltage dependence of steady-state inactivation elicited linear shifts in steady-state cocaine block, yet these manipulations did not affect the cocaine affinity of resting or inactivated channels. These data, as well as simulations used to predict block, indicate that state-dependent cocaine block depends on both steady-state inactivation and channel activation, although inactivation appears to have the predominant role.

Impediment to calcium influx and reactive oxygen production accounts for the inhibition of neutrophil Mac-1 Up-regulation and adhesion by tetrandrine

We studied the mechanisms by which the plant alkaloid tetrandrine (TTD) inhibits Mac-1-dependent neutrophil adhesion to fibrinogen. TTD (0.1-10 microM) significantly inhibited Mac-1 up-regulation and neutrophil adhesion, as induced by N-formyl-methionyl-leucyl-phenylalanine (fMLP) or phorbol-myristate-acetate (PMA). Treatment of neutrophils with fMLP or PMA caused a rapid influx of Ca++ and accumulation of reactive oxygen species (ROS), both of which have been shown to enhance neutrophil adhesion via Mac-1 up-regulation. Because TTD antagonizes Ca++ influx and abrogates ROS, we examined the relationship between Ca++ influx, ROS formation, and Mac-1 expression in TTD-inhibited neutrophil adhesion. TTD alone caused a slight but statistically significant increase in [Ca++]i with no effect on adhesion. In contrast, TTD as well as two Ca++ channel antagonists, verapamil and nifedipine, markedly diminished fMLP- and PMA-induced Ca++ influx, Mac-1 up-regulation, and adhesion. TTD also inhibited increases in [Ca++]i and adhesion induced by the ionophore A23187 but failed to inhibit those induced by thapsigargin, an agent mobilizing Ca++ from intracellular stores. Thus, TTD impeded Ca++ influx from outward to avert neutrophil adhesion. Similarly, TTD and two ROS scavengers, superoxide dismutase and catalase, abolished ROS production, Mac-1 up-regulation, and neutrophil adhesion. Ca++ and ROS, therefore, represent two essential signals for Mac-1 up-regulation upon fMLP or PMA stimulation. Our data suggest that the antiadherent effect of TTD is mediated, in part, by the inhibition of Ca++ influx and ROS formation, resulting in suppressed up-regulation of Mac-1 and, in turn, neutrophil adhesion to fibrinogen.

Psychosocial aspects of Taiwanese postpartum depression phenomenological approach: a preliminary report

To understand how Taiwanese women experience postpartum depression, a phenomenological study was conducted. A purposive sample of six mothers participated in the present study. All the subjects' interviews were tape recorded and then transcribed. The transcription of each subject's oral description of postpartum depression experience was analyzed using Colaizzi's phenomenological methodology. Three categories, with ten themes, were derived from the analysis. The first category is unbalanced role-enacting. It includes these four themes: (1) the discrepancies in the husband-wife relationship; (2) the shadowy position of a daughter-in-law; (3) the incompetence as a mother; and (4) the dilemma of a woman's identity. The second category is fragmented time-space representation. The themes included are: (5) cultural bondage; (6) loss of ideals; and (7) reinterpretation of family history. The third category is the uneasy self. It contains the themes of: (8) psychological disability; (9) sense of self-dissatisfaction; and (10) the notion or behavior of destruction.

Potassium currents in freshly dissociated uterine myocytes from nonpregnant and late-pregnant rats

In freshly dissociated uterine myocytes, the outward current is carried by K+ through channels highly selective for K+. Typically, nonpregnant myocytes have rather noisy K+ currents; half of them also have a fast-inactivating transient outward current (ITO). In contrast, the current records are not noisy in late pregnant myocytes, and ITO densities are low. The whole-cell IK of nonpregnant myocytes respond strongly to changes in [Ca2+]o or changes in [Ca2+]i caused by photolysis of caged Ca2+ compounds, nitr 5 or DM-nitrophene, but that of late-pregnant myocytes respond weakly or not at all. The Ca2+ insensitivity of the latter is present before any exposure to dissociating enzymes. By holding at -80, -40, or 0 mV and digital subtractions, the whole-cell IK of each type of myocyte can be separated into one noninactivating and two inactivating components with half-inactivation at approximately -61 and -22 mV. The noninactivating components, which consist mainly of iberiotoxin-susceptible large-conductance Ca2+-activated K+ currents, are half-activated at 39 mV in nonpregnant myocytes, but at 63 mV in late-pregnant myocytes. In detached membrane patches from the latter, identified 139 pS, Ca2+-sensitive K+ channels also have a half-open probability at 68 mV, and are less sensitive to Ca2+ than similar channels in taenia coli myocytes. Ca2+-activated K+ currents, susceptible to tetraethylammonium, charybdotoxin, and iberiotoxin contribute 30-35% of the total IK in nonpregnant myocytes, but <20% in late-pregnant myocytes. Dendrotoxin-susceptible, small-conductance delayed rectifier currents are not seen in nonpregnant myocytes, but contribute approximately 20% of total IK in late-pregnant myocytes. Thus, in late-pregnancy, myometrial excitability is increased by changes in K+ currents that include a suppression of the ITO, a redistribution of IK expression from large-conductance Ca2+-activated channels to smaller-conductance delayed rectifier channels, a lowered Ca2+ sensitivity, and a positive shift of the activation of some large-conductance Ca2+-activated channels.

Polymorphisms of twelve short tandem repeat loci in a Taiwanese population and their application in parentage testing

With the advancement of techniques in molecular biology, rapid, sensitive, and reliable methods of DNA typing for parentage testing have become available. In this study, we evaluated the usefulness of multiplex polymerase chain reaction (PCR) with 12 unlinked short tandem repeat (STR) loci for paternity testing in Taiwan. The genetic informativeness of this test was then compared with that of conventional human leukocyte antigen (HLA) analysis in 167 parentage studies. The 12 STR loci alone provided a cumulative power of exclusion of up to 0.9998. Paternity was excluded in 59 (35.3%) cases, including 40 of 112 paternity trios and 19 of 55 paternity duos. In the 40 trios in which paternity was excluded, a mean of 6 (range, 3-9) incompatible STR markers were in the 19 duos in which paternity was excluded, a mean of 4 (range, 1-8) incompatible STR markers were noted. In the 72 trios in which the alleged paternity could not be excluded, the mean probabilities of paternity (PP) were 90.6863% with HLA testing alone, 99.9847% with STR analysis alone, and 99.9972% with combined HLA and STR analysis. In the 36 duos in which the alleged paternity could not be excluded, the mean PPs were 81.4768% with HLA testing alone, 99.6124% with STR analysis alone, and 99.9145% with combined HLA and STR analysis. These results suggest that STR analysis is very powerful when used alone for paternity trio testing and when combined with conventional serologic HLA typing for duo parentage testing in the Taiwan population.

Twenty-four-hour intravenous and oral tracer studies with L-[1-13C]-2-aminoadipic acid and L-[1-13C]lysine as tracers at generous nitrogen and lysine intakes in healthy adults

BACKGROUND

This is a continuation of investigations of the relations between amino acid kinetics and amino acid dietary requirements in healthy adults.

OBJECTIVE

The aim was to investigate the 24-h pattern and rate of the metabolism of an L-[1-13C]-2-aminoadipic acid ([13C]AAA) tracer and of whole-body L-[1-13C]lysine ([13C]lysine) oxidation and balance in healthy, young adults receiving a generous intake of lysine.

DESIGN

Thirteen healthy adults were given an adequate, L-amino acid-based diet supplying 77 mg lysine x kg(-1) x d(-1) for 6 d before the tracer studies. Two subjects received [13C]AAA intravenously and 2 received it orally; 3 subjects received [13C]lysine intravenously and 6 received it orally. We measured 13CO2 output, plasma [13C]AAA and [13C]lysine enrichment, and urinary [13C]AAA.

RESULTS

[13C]AAA oxidation was estimated to be higher after the orally administered than after the intravenously administer tracer; plasma [13C]AAA was similar to urinary [13C]AAA. Whole-body lysine oxidation showed a rhythm that was induced by meal feeding. The intravenous [13C]lysine tracer gave mean estimates of lysine balances (lysine intake minus oxidation) that apparently were too low (-15.7 mg x kg(-1) x d(-1)) or too high (16.6 mg x kg(-1) x d(-1), P < 0.05 from zero balance) on the basis of urinary [13C]AAA or plasma [13C]lysine estimates of oxidation, respectively. For the orally administered tracer and plasma [13C]lysine enrichment, the mean balance was slightly positive (8.7 mg x kg(-1) x d(-1), P < 0.05 from zero).

CONCLUSIONS

Use of urinary [13C]AAA as an index of the enrichment of the precursor pool did not appear to significantly improve the estimate of the fasting and feeding components of daily lysine balance. For estimates of daily, whole-body lysine oxidation, we propose use of plasma [13C]lysine with a 24-h, orally administered tracer protocol.

Lysine point mutations in Na+ channel D4-S6 reduce inactivated channel block by local anesthetics

Voltage-gated Na+ channels are a primary target for local anesthetics (LAs). Open or inactivated Na+ channels usually have a severalfold higher affinity for LAs than do resting channels. Hille's modulated receptor hypothesis attributed the changes in LA affinity to state-dependent alterations in the conformation of the LA receptor. We expressed wild-type and mutant rat skeletal muscle (mu1) Na+ channels in human embryonic kidney cells to investigate the state-dependent modulation of LA receptor affinity. As an alternative approach to using alanine for point mutation, we substituted lysine (a hydrophilic residue) for native residues in the putative LA receptor located in D4-S6 of the mu1 Na+ channel. Lysine mutation at Y1586 did not alter resting channel affinity for cocaine but did reduce resting affinity at F1579K and N1584K by 2- and 3-fold, respectively. Compared with mu1, resting benzocaine block did not change at F1579K, decreased at N1584K, and increased at Y1586K. These effects on resting block could largely be accounted for by either steric/charge interference or cation-pi electron interactions between particular moieties on the LA and lysine. Surprisingly, lysine substitution at these residues allowed the channels to undergo steady state fast inactivation yet reduced inactivated channel block by cocaine by up to 27-fold and reduced the benzocaine-induced leftward shift in the h(infinity) curve by up to 22 mV. Our data suggest that transitions in channel state indeed invoke conformational changes in the LA receptor and that lysine mutations in the LA receptor region alter such conformational changes during the transition to the inactivated state.

Nitric oxide enhances the growth of U937 human leukemic cells through a cyclooxygenase-mediated pathway

The mechanisms of exogenous nitric oxide (NO)-enhanced growth of the U937 human myeloid leukemic cells were examined using sodium nitroprusside (SNP) as a NO donor. Treatment with 0.1 mM SNP for 72 h caused a 45 +/- 2% increase in U937 cell growth with significantly increased S/G2+M-phase and decreased G0/G1-phase of the cell cycle. The growth-enhancing effect of SNP was blocked by indomethacin, a cyclooxygenase inhibitor, but not by H7, a broad spectrum kinase inhibitor, or PD98059, a mitogen-activated protein kinase inhibitor. SNP treatment resulted in a dose-dependent increase in prostaglandin E2 (PGE2) production. Furthermore, the addition of exogenous PGE2 not only enhanced U937 cell growth but restored the indomethacin-inhibited mitogenic effect of SNP. We suggest that NO can enhance cell growth through activating the cyclooxygenase pathway and that PGE2 may be an effector molecule for NO-regulated cell proliferation. Our data provide a mechanistic insight into the regulatory role of NO in myelopoiesis.

Aortic valve stenosis causing a left-to-right shunt in persistent left superior vena cava communicating with the left atrium

This study demonstrated a rare anomaly of a persistent left superior vena cava draining into the left atrium in a patient with developing left-to-right shunt caused by bicuspid aortic stenosis. The venous system, including the coronary sinus, was otherwise normal. We believe that, in this anatomic situation, a marked increase in left ventricular impedance caused a moderate left-to-right shunt from the left atrium into the left innominate vein. At operation, the aortic valve was replaced with a mechanical prosthesis and the anomalous vein was ligated. The convalescence was uneventful.

Local anesthetic block of batrachotoxin-resistant muscle Na+ channels

Local anesthetics (LAs) are noncompetitive antagonists of batrachotoxin (BTX) in voltage-gated Na+ channels. The putative LA receptor has been delineated within the transmembrane segment S6 in domain IV of voltage-gated Na+ channels, whereas the putative BTX receptor is within segment S6 in domain I. In this study, we created BTX-resistant muscle Na+ channels at segment I-S6 (micro1-N434K, micro1-L437K) to test whether these residues modulate LA binding. These mutant channels were expressed in transiently transfected human embryonic kidney 293T cells, and their sensitivity to lidocaine, QX-314, etidocaine, and benzocaine was assayed under whole-cell, voltage-clamp conditions. Our results show that LA binding in BTX-resistant micro1 Na+ channels was reduced significantly. At -100 mV holding potential, the reduction in LA affinity was maximal for QX-314 (by 17-fold) and much less for neutral benzocaine (by 2-fold). Furthermore, this reduction was residue specific; substitution of positively charged lysine with negatively charged aspartic acid (micro1-N434D) restored or even enhanced the LA affinity. We conclude that micro1-N434K and micro1-L437K residues located near the middle of the I-S6 segment of Na+ channels can reduce the LA binding affinity without BTX. Thus, this reduction of the LA affinity by point mutations at the BTX binding site is not caused by gating changes induced by BTX alone. We surmise that the BTX receptor and the LA receptor within segments I-S6 and IV-S6, respectively, may align near or within the Na+ permeation pathway.

The influence of cryopreservation on cytokine production by human T lymphocytes

Human T lymphocytes isolated from peripheral blood were cryopreserved at -196 degreesC for different periods of 3, 14, 21, 35, and 50 days. Viability and cytokine-producing activity of T cells were examined before and after cryopreservation. A high recovery (90 +/- 1%) of viable T cells was obtained at each frozen period, indicating that a 10% loss of cells was due to the freezing process rather than the duration of cryopreservation. There was no difference in cell cycle distribution between PHA-treated fresh and frozen lymphocytes. Resting human T cells produced little or no cytokine. After stimulation of fresh T cells with PHA, an apparent increase in cytokine production was noted in IL-2 (35.5 +/- 8.3 pg/ml), IL-6 (1280.4 +/- 64.7 pg/ml), tumor necrosis factor-alpha (874.3 +/- 71.7 pg/ml), interferon-gamma (58.9 +/- 2.2 pg/ml), and granulocyte macrophage-colony-stimulating factor (59.5 +/- 4.4 colonies/5 x 10(4) bone marrow cells). Compared with PHA-activated fresh T cells, all the above cytokines did not diminish in their levels in conditioned medium from PHA-treated frozen T cells thawed at each storage period, suggesting that cryopreservation could well retain the cytokine-producing activity of human T lymphocytes. In addition, our results also revealed that cryopreservation rendered T lymphocytes more responsive to PHA in IL-2 production than fresh T cells.

Clotrimazole is a potent vasodilator of the rat coronary microcirculation

Clotrimazole (CLT), used in the treatment of patients with sickle cell disease, directly blocks Ca2+-activated K+ (K+<INF POS="STACK">Ca) channels in red cells and in portal vein smooth muscle cells by a cytochrome P450(cyt P450)-independent mechanism. Therefore, we examined the effects of CLT on vasomotor tone of coronary arterioles. Rat coronary arterioles (80-180 micro(m) in diameter) were studied in vitro in a pressurized no-flow state with a video microscopy. CLT (0.1 micromol/L) elicited in nonprecontracted vessels a small contraction (<10% baseline diameter, P < 0.05 vs time control), consistent with blockade of a hyperpolarizing K+ channel. However, similar contraction was produced by the cyt P450 blocker 17-octadecynoic acid (17-ODYA, 100 micromol/L), suggesting possible involvement of arachidonate metabolites of cyt P450. In contrast, microvessels precontracted with the thromboxane A2 analog U46619 dilated in response to CLT [>90% relaxation of the U46619-induced precontraction at 100 micromol/L (P < 0.01 vs time control)] and its structural analogs flutrimazole (FLT), UR-4055, UR4057, UR-4058, and UR-4059. This relaxation was cyt P450-independent, since the in vivo CLT metabolite (CLT-carbinol) was equipotent with CLT, and 17-ODYA did not promote relaxation. CLT-induced dilation was not inhibited by the nitric oxide synthase inhibitor NGnitro-l-arginine (100 micromol/L, P > 0.5) or affected by endothelial denudation (P > 0.5). Thus, CLT at concentrations >1 micromol/L is a potent vasodilator of rat coronary arterioles. This dilation is likely mediated through a vascular smooth muscle mechanism independent of cyt P450 and is not modulated by nitric oxide or by the endothelium. This effect may arise from CLT's reported ability to inhibit voltage-gated Ca2+ channels or to inhibit, in some tissues, Ca2+ release from intracellular stores. The CLT- and FLT-induced relaxation may be a property common to this class of drugs and have clinical applicability.

Tamoxifen-mediated anti-cellular effect against a choriocarcinoma cell line

The present study was undertaken to evaluate the efficacy of using steroid hormone antagonists tamoxifen and Ru486 for chemotherapy or chemoprevention of choriocarcinoma or other less malignant gestational trophoblastic diseases (GTDs) such as invasive mole. Using 4 trophoblast cell lines, we have shown that tamoxifen (>/= 2 microM) has anti-growth activity on the choriocarcinoma cell line BeWo but not on the other cell lines in a time and dose dependent manner while Ru486 invariably had no detectable effect. Based on a radioimmunoassay, we have been able to detect low levels of estrogen receptors on BeWo (6 +/- 0.4 fm/mg; Kd=438+/- 73 pM) and JEG-3 (6.55 +/- 1.2 fm/mg; Kd=710 +/- 42 pM) cells and progesterone receptors on HT (48.62 fm/mg; Kd=1,690 +/- 182 pM) and TL (8.46 fm/mg; Kd=1,540 +/- 115 pM) cells. However, there is no definite correlation between steroid responsiveness and the presence of the receptors. The mechanism of our observed tamoxifen-mediated anti-cellular effect is uncertain and characteristics commonly associated with apoptotic cell death were not observed. The level of neither wild-type nor mutant forms of the p53 protein correlated with sensitivity to tamoxifen. Our results suggest that estrogen may be a growth hormone for some trophoblasts and tamoxifen may be potentially useful for the treatment of selected cases of choriocarcinoma or other trophoblastic diseases.

Allogeneic peripheral blood stem cell transplantation and early detection of donor engraftment by polymerase chain reaction

Patients with hematologic malignancy or severe aplastic anemia after myeloablative chemo- and radiotherapy were given granulocyte colony-stimulating factor (G-CSF)-mobilized, cryopreserved allogeneic peripheral blood stem cells (PBSCs) from 15 healthy donors who were either human leukocyte antigen (HLA)-matched siblings (n = 13) or haploidentical offspring (2). Polymerase chain reaction-amplified short tandem repeat genotyping was used for early confirmation of donor engraftment after PBSC transplantation (PBSCT). A standard cyclosporine A/methotrexate combination was used to prevent acute graft-versus-host disease (GVHD). All donors, including one in the third trimester of pregnancy, tolerated G-CSF administration and 3-day PBSC harvesting procedures well. Engraftment was prompt for all patients; it was verified using a panel of 12 human polymorphic short tandem repeat loci from bone marrow as early as 7 days posttransplantation. This status was maintained until relapse, when mixed chimerism was detected using the polymerase chain reaction. A minimum resurgence of recipient cells to 1% of the population was required to detect chimerism. The median times to recovery of the absolute neutrophil count to greater than 0.5 x 10(9)/L and the sustained platelet count to greater than 20 x 10(9)/L without transfusion were 10 and 12 days after PBSCT, respectively. Six patients experienced acute GVHD, Grade I in two patients and Grade II in four, including two HLA-haploidentical recipients. Chronic GVHD was noticed in three of the 11 patients who were followed for at least 100 days after PBSCT. Ten patients were still alive at the latest follow-up and have been disease free for a median of 278 days (range 60-671). Five patients died from causes other than graft failure: three from leukemia relapse and two from transplant-related complications. The results confirm that G-CSF can be safely administered to healthy donors and that engraftment after allogeneic PBSCT is fast and durable. Complete chimerism can be detected early by genomic analysis. PBSCT may offer an alternative to bone marrow transplantation.

Point mutations in segment I-S6 render voltage-gated Na+ channels resistant to batrachotoxin

Batrachotoxin (BTX) is a steroidal alkaloid that causes Na+ channels to open persistently. This toxin has been used widely as a tool for studying Na+ channel gating processes and for estimating Na+ channel density. In this report we used point mutations to identify critical residues involved in BTX binding and to examine if such mutations affect channel gating. We show that a single asparagine --> lysine substitution of the rat muscle Na+ channel alpha-subunit, mu1-N434K, renders the channel completely insensitive to 5 microM BTX when expressed in mammalian cells. This mutant channel nonetheless displays normal current kinetics with minimal changes in gating properties. Another substitution, mu1-N434A, yields a partial BTX-sensitive mutant. Unlike wild-type currents, the BTX-modified mu1-N434A currents continue to undergo fast and slow inactivation as if the inactivation processes remain functional. This finding implies that the mu1-N434 residue upon binding with BTX is critical for subsequent changes on gating; alanine at the mu1-434 position apparently diminishes the efficacy of BTX on eliminating Na+ channel inactivation. Mutants of two adjacent residues, mu1-I433K and mu1-L437K, also were found to exhibit the identical BTX-resistant phenotype. We propose that the mu1-I433, mu1-N434, and mu1-L437 residues in transmembrane segment I-S6 probably form a part of the BTX receptor.

Mesenteric and skeletal muscle microvascular responsiveness in subacute sepsis

This study was performed to assess the effects of subacute sepsis in rats on the in vitro reactivity of arterioles (internal diameter, 100-150 microm) to alpha1- and alpha2-adrenergic stimulation and to angiotensin II. Male Sprague-Dawley rats were rendered septic by intraperitoneal implantation of a gelatin capsule containing sterile rat feces and 1 x 10(6) viable colony forming units of Escherichia coli. Control rats underwent sham laparotomy and implantation of a gelatin capsule containing only sterile feces. In vitro reactivity of arterioles from mesentery and skeletal muscle were studied 48 h later in a pressurized (50 mmHg) no flow state using videomicroscopy. Subacute sepsis decreased the contractile response of nonprecontracted microvessels from both anatomical sites to phenylephrine (both p < .01 versus control) and blunted the relaxation response to staurosporine (both p < .01), an inhibitor of protein kinase C. The small contraction to angiotensin II of mesenteric vessels was inhibited by sepsis (p < .05) but was unaltered in the skeletal muscle microcirculation. In the precontracted mesenteric microvessels from septic rats, endothelium-dependent relaxation to clonidine and to adenosine 5'-diphosphate were decreased (both p < .01 versus control), whereas in skeletal muscle microvessels, clonidine and adenosine 5'-diphosphate elicited constriction (both p < .01). Relaxation to the endothelium independent vasodilators sodium nitroprusside and pinacidil was preserved across all vessels. In conclusion, mesenteric and skeletal muscle microvascular responses to angiotensin II and alpha1- and alpha2-adrenergic stimulation are altered in subacute sepsis. This may in part lead to systemic hypotension and altered organ perfusion during states of chronic sepsis.

pHe, [Ca2+]e, and cell death during metabolic inhibition: role of phospholipase A2 and sarcolemmal phospholipids

This study measures cellular lactate dehydrogenase (LDH) release during metabolic inhibition as a monitor of sarcolemmal integrity as affected by variation of external pH (pHe) and Ca2+ concentration ([Ca2+]e). The sigmoidal relationship between pHe and LDH release and pHe and net Ca2+ uptake was essentially identical with the 50% maximal value occurring at pH 7.0 for both. This suggests that a process(es) sensitive to both pHe and [Ca2+]e plays a role in cell lysis during the course of metabolic inhibition. Variation of pHe during metabolic inhibition did not alter the decline in cellular ATP, nor did it affect changes in sarcolemmal phospholipid topology. Intracellular pH followed changes of pHe with a few minutes lag. Cell lysis increased in a graded manner as pHe and [Ca2+]e were increased, but pHe was the sole determinant of lysis, i.e., [Ca2+]e level had no effect, at the lowest (6.2) and the highest (8.0) pHe levels. pHe variation did not affect the release of radiolabeled arachidonic acid, nor did inhibitors of phospholipase A2 (PLA2) affect cell lysis at varying pHe. Therefore, cellular PLA2 activation could not be implicated for a role in cell lysis in the present model of metabolic inhibition. Alternatively, we propose that Ca2+ binding to the cytoplasmic leaflet, in combination with membrane alterations secondary to the metabolic insult, combine to destabilize the sarcolemma (20). This Ca2+ binding to the negatively charged phosphatidylserine results in the expression of the bilayer destabilizing effect of phosphatidylethanolamine. This Ca2+ binding is greatly diminished by lowered pH, resulting in an attenuation of cell lysis.

Induction of apoptosis in human leukemic U937 cells by tetrandrine

Tetrandrine, a calcium channel antagonist, is a plant alkaloid possessing various pharmacological activities including anti-tumor activity. We studied tetrandrine to determine whether or not this anti-tumor effect occurs through induction of apoptosis. Tetrandrine inhibited both proliferation and clonogenicity of human leukemic U937 cells at an optimal concentration of 2.5 microg/ml. This growth inhibition was dose and time dependent, and accompanied with evidence of apoptotic changes. The characteristic morphological changes of apoptosis were observed in U937 cells under light microscopy and DNA fragmentation was noted by gel electrophoresis. Moreover, flow cytometric detection of surface phosphatidyl serine expression of U937 cells after treatment with tetrandrine confirmed the induction of apoptosis in these cells. The induction of apoptosis by tetrandrine would appear to proceed via non-Ca2+-dependent pathways.

Severe haemorrhage partially reverses moderate haemorrhage-induced decrease in intestinal vascular capacitance

The purpose of the present study was to compare the effect of severe haemorrhage with moderate haemorrhage on intestinal vascular capacitance. In 12 chloralose-anaesthetized pigs, moderate and subsequent severe haemorrhage was induced by removal of 15 and 25% of blood volume, respectively. Six of the animals were vagotomized prior to induction of haemorrhage. The portal vein pressure/intestinal blood volume (P-V) relationship was measured by using blood pool scintigraphy and varying portal vein pressure. Moderate haemorrhage resulted in a leftward shift of the P-V relationship towards the pressure axis with decreases in cardiac output, portal blood flow and arterial pressure, and an increase in heart rate. Severe haemorrhage shifted the P-V relationship back towards the volume axis compared with moderate haemorrhage, with further decreases in cardiac output, portal blood flow and arterial pressure. While moderate haemorrhage reduced intestinal blood volume at a portal vein pressure of 7 mmHg (Vp7) to 81 +/- 3% of the control value (P < 0.01), severe haemorrhage increased Vp7 to 88 +/- 1% of the control value (P < 0.05 compared with moderate haemorrhage). After vagotomy, moderate haemorrhage decreased Vp7 to 84 +/- 4% of the control value (P < 0.01), whereas Vp7 did not change significantly after severe haemorrhage (Vp7 increased to 86 +/- 1% of the control value). Thus, severe haemorrhage is associated with an increase in intestinal vascular capacity compared with moderate haemorrhage. This increase is mediated in part via the cardiac vagal reflex. The attenuation of intestinal venoconstriction during severe haemorrhage probably contributes to further decreases in cardiac output and arterial pressure by redistribution of blood to the peripheral circulation.

Dependence of cardiac cell Ca2+ permeability on sialic acid-containing sarcolemmal gangliosides

The specific removal of negatively-charged sialic acid by neuraminidase produces a large increase in cardiac myocyte Ca uptake (17.3 +/- 1.1 mmol Ca/kg dry weight) and marked cell contracture. Importantly, the insertion of the negatively-charged amphiphile dodecyl sulfate in the sarcolemma eliminates the increased calcium uptake and preserves contractile function. In the present study, we further examine the role of sialic acid-Ca interaction and, specifically, the role of gangliosides (sialic acid-containing glycolipids) in cardiac cells' Ca permeability. Neonatal cell culture and adult ventricular myocytes were used. The major findings of this study are: (1) while dodecyl sulfate inhibits cellular calcium uptake and contracture development induced by sialic acid removal, cationic and neutral amphiphiles are without effect. (2) Ca channel blockers (nifedipine and protamine) and the Na/Ca exchange inhibitor Ni do not modify the effect of sialic acid removal. (3) A non-classical-channel related whole-cell current appears and increases after 21 +/- 2.2 min treatment with 0.02 U/ml neuraminidase (n = 4). Incubation with neuraminidase in the presence of dodecyl sulfate greatly delays the appearance of these currents to 44.4 +/- 6.1 min (n = 4). (4) The use of a specific probe for GM1 ganglioside, the cholera toxin B subunit (3 micrograms/ml), induces a moderate but clear increase in cellular Ca (1.63 +/- 0.3 mmol Ca kg dry weight; n = 8). However, this increase was not modified by treatment with dodecyl sulfate. (5) Finally, 50 mU/ml endoglycoceramidase, an enzyme which specifically cleaves the link between the sialic acid-containing oligosaccharide and ceramide of gangliosides, induced a significant increase in Ca uptake (4.4 +/- 0.9 mmol Ca kg dry weight, n = 4). These results indicate the importance of negatively charged sialic acid-containing gangliosides in the maintenance of cardiac cell physiological Ca permeability. The increase in Ca uptake induced by the removal of sialic acid seems to be mediated by development of a Ca "leak" via other than classical cation channels.

[Fraction analysis of the involvement of multiple risk factors in the etiology of lung cancer: risk factor interactions in a case-control study for lung cancer in females]

A 1:1 matched case-control study of etiologic fraction (EF) of female lung cancer was conducted in Guangdong Province. 200 female cases with primary lung cancer were selected and 200 female controls matched by age, area of residence and education from five hospitals. Multiple conditional logistic regression analysis turned out that passive smoking from spouse, bad ventilation in kitchen, liking for pickles or salted fish, history to chronic bronchitis, family history of tumour, pulmonary tuberculosis, taking oral contraceptive were the independent risk factors of female lung cancer (OR = 2.16-40.55, P < 0.05). EF of the independent risk factors were 0.535, 0.432, 0.252, 0.124, 0.115, 0.072, 0.069 respectively. The interactions between passive smoking from spouse and risk factors which included taking oral contraceptive, family history of tumour, bad ventilation in kitchen, history of pulmonary tuberculosis, liking for pickles or salted fish were analyzed. The result revealed that EF (AxB) (aetiologic fraction attributable to interaction) were 0.848, 0.499, 0.479, 0.416, 0.346 respectively. The interaction index were 0.906, 0.543, 0.578, 0.427, 0.441. These findings indicate passive smoking from spouse, particularly those had a history of taking oral contraceptive, increases the risk of female lung cancer.

Beta-adrenergic regulation of the cerebral microcirculation after hypothermic cardiopulmonary bypass

BACKGROUND

The beta-adrenergic-cAMP pathway importantly regulates cerebral blood flow. Previous studies have found that normothermic cardiopulmonary bypass (CPB) is associated with reduced cerebral beta-adrenoceptor-mediated relaxation.

METHODS AND RESULTS

In order to examine the effects of hypothermic CPB on regulation of perfusion by the beta-adrenergic-cAMP pathway, pigs were placed on moderately (25 degrees C) or profoundly hypothermic (16 degrees C with 1 hour of circulatory arrest) or normothermic (37 degrees C) CPB for 2 hours. After normothermic perfusion for 15 minutes and separation from CPB, cerebral microvascular responses to the beta-adrenoceptor agonist isoproterenol (ISO), the adenylate cyclase activator forskolin, and the stable cAMP analogue 8-bromo-cAMP were examined in vitro in a pressurized, no-flow state. Baseline internal carotid artery blood flow was similar and unchanged after rewarming in the three experimental groups. However, ISO (100 micromol/L) elicited less relaxation after moderately hypothermic CPB (75+/-6%, P<.05 versus control, percent of U46619 induced precontraction) and profoundly hypothermic circulatory arrest (42+/-5%, P<.05) than in vessels from uninstrumented controls (91+/-2%) or after normothermic CPB (84+/-4%). The relaxation to forskolin was reduced after profoundly hypothermic circulatory arrest (83+/-3%, P<.05), but was similar in the other groups (92+/-2% control). Surprisingly, relaxation induced by 8-bromo-cAMP was markedly reduced after normothermic CPB, and this change was directly related to temperature during CPB. The intraluminal exposure of vessels to zymosan-induced complement activated serum had no effect on relaxation to ISO, while 2 hours of exposure of vessels to ISO caused a dose-dependent reduction in subsequent relaxation to ISO, but not to forskolin.

CONCLUSIONS

Moderately hypothermic CPB or PHCA desensitizes alpha-adrenoceptors more than normothermic CPB. This is likely due in part to the exposure of vessels to endogenous catecholamines during CPB. Thus, whereas baseline cerebral blood flow is similar after normothermic and hypothermic CPB, beta-adrenergic responses are markedly abnormal.