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.

Sodium and calcium inward currents in freshly dissociated smooth myocytes of rat uterus

Freshly dissociated myocytes from nonpregnant, pregnant, and postpartum rat uteri have been studied with the tight-seal patch-clamp method. The inward current contains both INa and ICa that are vastly different from those in tissue-cultured material. INa is abolished by Na+-free medium and by 1 microM tetrodotoxin. It first appears at approximately -40 mV, reaches maximum at 0 mV, and reverses at 84 mV. It activates with a voltage-dependent tau of 0.2 ms at 20 mV, and inactivates as a single exponential with a tau of 0. 4 ms. Na+ conductance is half activated at -21.5 mV, and half inactivated at -59 mV. INa reactivates with a tau of 20 ms. ICa is abolished by Ca2+-free medium, Co2+ (5 mM), or nisoldipine (2 microM), and enhanced in 30 mM Ca2+, Ba2+, or BAY-K 8644. It first appears at approximately -30 mV and reaches maximum at +10 mV. It activates with a voltage-dependent tau of 1.5 ms at 20 mV, and inactivates in two exponential phases, with tau's of 33 and 133 ms. Ca2+ conductance is half activated at -7.4 mV, and half inactivated at -34 mV. ICa reactivates with tau's of 27 and 374 ms. INa and ICa are seen in myocytes from nonpregnant estrus uteri and throughout pregnancy, exhibiting complex changes. The ratio of densities of peak INa/ICa changes from 0.5 in the nonpregnant state to 1.6 at term. The enhanced role of INa, with faster kinetics, allows more frequent repetitive spike discharges to facilitate simultaneous excitation of the parturient uterus. In postpartum, both currents decrease markedly, with INa vanishing from most myocytes. Estrogen-enhanced genomic influences may account for the emergence of INa, and increased densities of INa and ICa as pregnancy progresses. Other influences may regulate varied channel expression at different stages of pregnancy.

Longitudinal weight changes, length of survival, and energy requirements of long-term care residents with dementia

OBJECTIVE

We hypothesized that institutionalized patients with dementia, who frequently have feeding problems and require supervised and assisted feeding, would lose more weight during their residency than nondemented, independently functioning residents and have compromised survival. To test this hypothesis, we examined the survival and longitudinal changes in weight of two cohorts of institutionalized residents with dementia and compared these cohorts with a cohort of nondemented residents. We also measured the resting energy expenditures of a subset of the subjects with dementia as an indicator of their energy needs.

DESIGN

A longitudinal cohort study with retrospective baseline chart review and subsequent follow-up of monthly weights and mortality over 4 years.

SETTING

A 725-bed long-term care institution with specified levels of care.

SUBJECTS

Two cohorts of residents with dementia, one consisting of subjects who required total care throughout their institutional stay (n = 31) and another group who did not initially require total care (n = 48); these were compared with a cohort with normal mentation who were functionally independent in their daily activities (n = 26). The total number of subjects was 105.

MEASUREMENTS

Demographics, medical problems, and medications by chart review; functional and mental status evaluations; longitudinal monthly weights and mortality for the 48-month study period; and resting energy expenditures by indirect calorimetry.

MAIN RESULTS

Residents with dementia had lower weights on admission and throughout their stay than nondemented, independently functioning residents, and they were more likely to have a weight loss of 10 lbs or more at some point during the 4-year study period. However, their mean weights did not change during the study period. The mean survival from admission of those demented residents who died was more than 3 years. Resting energy expenditures of women residents with advanced dementia were 12% lower than predicted from the Harris Benedict equations.

CONCLUSION

Dementia is not necessarily associated with unremitting weight loss during institutionalization despite the frequent occurrence of feeding difficulties and temporary weight loss. This may be caused partly by the lower than expected resting energy expenditures and, hence, energy needs of affected residents as their dementia progresses. Demented residents weighed significantly less than nondemented, independently functioning residents throughout their institutional stay. Nevertheless, nursing staff are able to maintain weight and survival for extended periods even in very impaired residents.

Coronary sinus stenosis as a late complication of catheter ablation in Wolff-Parkinson-White syndrome

This report describes a patient who developed stenosis of coronary sinus and cardiac veins five years after application of electric shock currents to the posterior mitral annulus and posteroseptal region of the tricuspid annulus for ablation of a left posterior accessory pathway and a right posteroseptal accessory pathway. This is the first angiographic documentation of coronary sinus stenosis as a late complication of electric ablation of accessory pathway.

Cardiopulmonary bypass alters vasomotor regulation of the skeletal muscle microcirculation

BACKGROUND

Cardiopulmonary bypass (CPB) is associated with alterations in the regulation of organ perfusion and vascular permeability. The purpose of this study was to examine the effects of hypothermic CPB on the regulation of the skeletal muscle microcirculation and the modulating influence of the priming solution.

METHODS

Sheep were placed on hypothermic CPB with a prime of either Pentastarch hydroxylethyl starch (HS) solution (n = 7), a solution in which HS is conjugated with deferoxamine (n = 7), or Ringer's lactate solution (n = 7). Sheep were placed on hypothermic CPB (27 degrees C) for 90 minutes while the heart was protected with cold blood cardioplegia. Sheep were then separated from CPB and perfused for an additional 3 hours off CPB. Hemodynamics and total water content were measured.

RESULTS

In vitro relaxation responses of gracilis muscle arterioles (70 to 180 microns) to the endothelium-dependent agent acetylcholine, the endothelium-independent cyclic GMP-mediated vasodilator sodium nitroprusside, the beta-adrenergic agonist isoproterenol, and the adenylate cyclase activator forskolin were studied. No statistically significant hemodynamic differences were observed between groups. However, weight gain was significantly less when the priming solution was HS or HS-deferoxamine compared to when Ringer's lactate was used. Skeletal muscle arteriolar relaxations to the endothelium-dependent vasodilator acetylcholine and the beta-adrenergic agonist isoproterenol were impaired after CPB in the HS and Ringer's lactate groups. Acetylcholine response was preserved in the HS-deferoxamine group, whereas the response to isoproterenol remained impaired. The responses to sodium nitroprusside and forskolin were similar in all groups.

CONCLUSIONS

Skeletal muscle microvascular endothelium-dependent relaxation and beta-adrenergic relaxation are reduced after CPB using either a crystalloid or HS prime. Skeletal muscle microvascular endothelial dysfunction may be attributable to oxygen-derived free radical-mediated injury, whereas altered beta-adrenergic regulation is attributable to mechanisms other than the generation of oxygen-derived free radicals during CPB.

Differences in steady-state inactivation between Na channel isoforms affect local anesthetic binding affinity

Cocaine and lidocaine are local anesthetics (LAs) that block Na currents in excitable tissues. Cocaine is also a cardiotoxic agent and can induce cardiac arrhythmia and ventricular fibrillation. Lidocaine is commonly used as a postinfarction antiarrhythmic agent. These LAs exert clinically relevant effects at concentrations that do not obviously affect the normal function of either nerve or skeletal muscle. We compared the cocaine and lidocaine affinities of human cardiac (hH1) and rat skeletal (mu 1) muscle Na channels that were transiently expressed in HEK 293t cells. The affinities of resting mu 1 and hH1 channels were similar for cocaine (269 and 235 microM, respectively) and for lidocaine (491 and 440 microM, respectively). In addition, the affinities of inactivated mu 1 and hH1 channels were also similar for cocaine (12 and 10 microM, respectively) and for lidocaine (19 and 12 microM, respectively). In contrast to previous studies, our results indicate that the greater sensitivity of cardiac tissue to cocaine or lidocaine is not due to a higher affinity of the LA receptor in cardiac Na channels, but that at physiological resting potentials (-100 to -90 mV), a greater percentage of hH1 channels than mu 1 channels are in the inactivated (i.e., high-affinity) state.

Change in heart rate dynamics after aerobic training detected by approximate entropy and its association with orthostasis

Findings from the 1973 Skylab mission and early studies led to the conclusion that high level of aerobic capacity might be detrimental to the orthostatic tolerance of returning astronauts. Numerous studies have addressed the problem with conflicting results, further work is needed to establish the relationship between aerobic capacity and orthostasis. During the last two decades, the technique for heart rate variability (HRV) signal analysis developed and have provided a non-invasive probe to examine quantitatively changes in cardiac autonomic balance. In the past, spectral analysis has been used in these studies. During the early 90's, a new mathematical approach and formula termed approximate entropy(ApEn) has been introduced as quantification of regularity and complexity. More recently, ApEn has been used to quantitate the loss of normal nonlinear heart rate variability in a variety of pathological conditions, aging, as well as bed rest deconditioning. The present study was undertaken to assess the effect aerobic training on orthostatic tolerance and HRV analyzed by both conventional AR spectral and ApEn analysis.