Manipulating topological transformations of polar structures through real-time observation of the dynamic polarization evolution.

Topological structures based on controllable ferroelectric or ferromagnetic domain configurations offer the opportunity to develop microelectronic devices such as high-density memories. Despite the increasing experimental and theoretical insights into various domain structures (such as polar spirals, polar wave, polar vortex) over the past decade, manipulating the topological transformations of polar structures and comprehensively understanding its underlying mechanism remains lacking. By conducting an in-situ non-contact bias technique, here we systematically investigate the real-time topological transformations of polar structures in PbTiO3/SrTiO3 multilayers at an atomic level. The procedure of vortex pair splitting and the transformation from polar vortex to polar wave and out-of-plane polarization are observed step by step. Furthermore, the redistribution of charge in various topological structures has been demonstrated under an external bias. This provides new insights for the symbiosis of polar and charge and offers an opportunity for a new generation of microelectronic devices.

Electrophysiological effects of protopine in cardiac myocytes: inhibition of multiple cation channel currents.

Protopine (Pro) from Corydalis tubers has been shown to have multiple actions on cardiovascular system, including anti-arrhythmic, anti-hypertensive and negative inotropic effects. Although it was thought that Pro exerts its actions through blocking Ca(2+) currents, the electrophysiological profile of Pro is unclear. The aim of this study is to elucidate the ionic mechanisms of Pro effects in the heart. In single isolated ventricular myocytes from guinea-pig, extracellular application of Pro markedly and reversibly abbreviates action potential duration, and decreases the rate of upstroke (dV/dt)(max), amplitude and overshoot of action potential in a dose-dependent manner. Additionally, it produces a slight, but significant hyperpolarization of the resting membrane potential. Pro at 25, 50 and 100 microM reduces L-type Ca(2+) current (I(Ca,L)) amplitude to 89.1, 61.9 and 45.8% of control, respectively, and significantly slows the decay kinetics of I(Ca,L) at higher concentration. The steady state inactivation of I(Ca,L) is shifted negatively by 5.9 - 7.0 mV (at 50 - 100 microM Pro), whereas the voltage-dependent activation of I(Ca,L) remains unchanged. In contrast, Pro at 100 microM has no evident effects on T-type Ca(2+) current (I(Ca,T)). In the presence of Pro, both the inward rectifier (I(K1)) and delayed rectifier (I(K)) potassium currents are variably inhibited, depending on Pro concentrations. Sodium current (I(Na)), recorded in low [Na(+)](o) (40 mM) solution, is more potently suppressed by Pro. At 25 microM, Pro significantly attenuated I(Na) at most of the test voltages (-60 approximately +40 mV, with a 53% reduction at -30 mV. Thus, Pro is not a selective Ca(2+) channel antagonist. Rather, it acts as a promiscuous inhibitor of cation channel currents including I(Ca,L), I(K), I(K1) as well as I(Na). These findings may provide some mechanistic explanations for the therapeutic actions of Pro in the heart.

The blocking effect of BmP02, one novel short-chain scorpion peptide on transient outward K(+) channel of adult rat ventricular myocyte.

Two components F-2-7-4 and F-2-7-5, each composed of 28 amino acid residues, were purified from the venom of Buthus martensi Karsch by an opportune procedure with cation-exchange column chromatography and repeated HPLC. Both components were totally accounted to about 0. 88% dry weight of the crude venom. The molecular weights of both components were determined to be 2950 and 2935 by mass spectrometry, which were fully coincidence with that of the known novel short-chain peptides BmP02 and BmP03, respectively [Romi-Lebrun R, Martin-Eauclaire M-F, Escoubas P, Wu FQ, Lebrun B, Hisada M, Nakajima T. Characterization of four toxins from Buthus martensi scorpion venom, which act on apamin-sensitive Ca(2+)-activated K(+) channels. Eur J Biochem 1997;145:457-464]. In addition, the sequence of component F-2-7-4 was analyzed to be the same as that of BmP02. The components F-2-7-4 and F-2-7-5 purified in this study were, thus, finally distinguished to be BmP02 and BmP03 from the same venom. Using whole cell patch-clamp recording, it was found that BmP02 diminished the current of transient outward K(+) channel in adult rat ventricular myocyte in a concentration-dependent manner. The inhibitory effect was reversible. Dynamic studies showed that the activation, inactivation and recovery processes of the transient outward K(+) channel were not changed significantly after applying of BmP02. In addition, when BmP02 was applied to guinea pig ventricular myocyte, both delayed and inward rectified K(+) currents showed no change compared with the control. The results suggest strongly that BmP02 or -like peptides from scorpion venom may provide a useful probe for the studying of transient outward K(+) channel in rat ventricular myocyte.

Effects of intermittent hypoxia on action potential and contraction in non-ischemic and ischemic rat papillary muscle.

Although it has been reported that intermittent hypoxia had the anti-arrhythmia effect, little is known about the effects on the action potential (AP) and contraction of papillary muscle, as well as the mechanism of anti-arrhythmia. The purpose of present study is to observe the effects of intermittent hypoxia on action potential and contraction of papillary muscle in rat left ventricle simultaneously using conventional intracellular microelectrode and contraction recording. The effects of intermittent hypoxia on AP and contraction during ischemic solution perfusion were also investigated. After exposed to intermittent hypoxia (six hours daily) for 42 days (IH42), duration (APD20) of 20%, 50% (APD50) and 90% (APD90) repolarization of AP prolonged significantly compared with animals in control (Con). Effective refractory period (ERP) in IH42 also prolonged significantly. Perfused with mimic ischemic solution, the changes of electric and mechanical activities in IH42 and in 28 days exposure to intermittent hypoxia (IH28) were much smaller than that in Con and IH14. The result of the study suggested that intermittent hypoxia prolonged the APD and ERP, offered the resistance against the ischemic damage on myocardium, which may be the electrophysiological basis of the anti-arrhythmia of intermittent hypoxia.

[Effect of acute hypoxia on L-type calcium current of the ventricular myocytes of guinea-pig].

When the conventional whole cell recording technique is used to study the inward calcium current in cardiac cells, the "Run down" phenomenon of calcium channel would prevent sufficient time of recording desirable for adequate experimental analysis. The "Run down" phenomenon could be minimized by using nystatin-whole cell recording technique in isolated guinea-pig ventricular cells. The inward L-type calcium current could be maintained at a steady level for up to more than 100 min, showing the presence of an endogenous steady calcium ion buffering mechanism. With nystatin-whole cell recording, the L-type calcium current after 10 min acute hypoxia (Po2 4 +/- 0.7 kPa) was inhibited (peak amplitude decreased) and the I-V relation was shifted upward. The inward calcium current showed no recovery after 10 min reoxygenation. The peak amplitude was lower than that of the control. The results suggested that the decrease of action potential duration (APD) under acute hypoxia was not only due to increase of outward potassium current, but also a decrease of inward calcium current. All these phenomena may be related to some inhibition of phosphorylation of the L-type calcium channel in the cardiac cells under hypoxia.

[Role of central vasopressin in the maintenance of cardiovascular activities during acute hypoxia].

To investigate whether central vasopressin play a role in the maintenance of cardiovascular activities of rats exposed to acute hypoxia, blood pressure, heart rate, pressures of left and right ventricles and their dp/dt were monitored in rats anesthetized with urethane. The rats were divided into three groups, each of which received intracerebroventricular injection (icv.) of V1- and V2-vasopressinergic antagonists (4 micrograms, each) and equivolumetric vehicle (8 microliters, served as control group). Ten min after icv. three groups of rats were exposed to acute hypoxia (9% O2 in N2) for 15 min before reoxygenation. During hypoxia, MBP, HR, LVSP and LV + dp/dtmax of V1-antagonist treated group decreased more significantly than those of the control group (P < 0.01). After reoxygenation there were no significant differences between both groups. V1-antagonist and the vehicle had no detectable effect on the cardiovascular parameters during normoxia. Although icv. V2-antagonist caused a transient augmentations of HR, MBP, LVSP and LV + dp/dtmax except for RVSP and RV + dp/dtmax, there were no significant differences in cardiovascular activities between V2-antagonist treated group and control group during hypoxia and reoxygenation. These results indicate that central endogenous vasopressin play an important role in the maintenance of cardiovascular activities during hypoxia via its V1-receptor without involving V2-receptor. The central vasopressin does not have a tonic effect on cardiovascular activities under normal conditions.

[Role of cytosolic calcium balance on cell injury in cultured bovine aortic endothelial cells during hypoxia and reoxygenation].

Making use of an in vitro model of bovine aortic endothelial cell monolayers, the cell viability and changes of intracellukar calcium concentration of the preparation were submitted to hypoxia with or without reoxygenation. It was shown that the cell viability declined under hypoxia but increased under reoxygenation when the endothelial cells were incubated in calcium-free HBSS, as compared with control HBSS incubation. It was observed that a significant reduction of intracellular calcium from 99 to 69 nmol/L during 2 h of hypoxia, which was further decreased in Ca(2+)-free HBSS medium. After 4 h hypoxia followed by 40 min reoxygenation, [Ca2+]i recovered to the nomal concentration. It is speculated that the calcium homeostasis may be an important condition for cells to carry out normal function and either decrease or increase of [Ca2+]i may injury bovine aortic endothelial cells.

[Effect of acute hypoxia on ATP-sensitive potassium current in ventricular myocytes of guinea-pig].

The role of the ATP-sensitive potassium channel in arrhythmogenesis is not clearly understood. Cellular K+ loss and accumulation of [K+]o may contribute to genesis of malignant ventricular arrhythmia during myocardial ischemia. In the present study, acute hypoxia simply caused a partial decrease in K+ efflux at normal [K+]o, which was not sensitive to glibenclamide (5 x 10(-3) mmol/L). However, at a higher concentration of [K+]o (10.8 mmol/L), the outward K+ current increased dramatically after 10 min hypoxia, which was accompanied with an irreversible hypercontracture and eventual death of the cell. The I-V relation was linear with increasing repolarization, which was blocked by glibenclamide, an antagonist of ATP-sensitive potassium channel. The results suggest that the increased K+ current is ATP-sensitive and is facilitated by accumulation of the [K+]o.

[Effects of hypoxia on myoglobin in cultured rat myocytes].

The effects of hyoxia and reoxygenation on myoglobin (Mb), cAMP, myocardial contractility and the effects of theophylline (an inhibitor of phosphodiesterase), procaine (an inhibitor of SR calcium release) on Mb expression were studied in cultured myocytes under hypoxic condition. Our results showed that hypoxia increased the Mb expression, but decreased cAMP and myocardial contractility. All these effects of hypoxia were recovered upon reoxygenation. The increase of Mb expression requires the participation of intracellular calcium and cAMP.

[Differences between effects of hypoxia on rabbit aorta and pulmonary artery].

The difference of morphological injury between rabbit aorta and pulmonary artery was compared after the animal was exposed to the altitude 5 km (PO2 = 10.8 kPa) for 24 h. Hypoxia caused subendothelial edema, increased vacuoles and injured mitochondria and endoplasmic reticulums in both kinds of endothelial cells. The impairment of pulmonary artery was obviously more severe than aorta and its smooth muscle cells were also affected. Forthermore, the exposure increased mitochondria in pulmonary artery endothelial cells. Bubbled with a mixture air of 95% N2-5% CO2 (PO2 = 4 kPa) led to an increase of pulmonary in tension, while hypoxia to the same extent induced aorta relaxation. These results indicate that hypoxia produces the differential effects on these two kinds of vessels, providing a possible explanation for the production of hypoxic pulmonary hypertension.

[Inhibition of transient outward potassium current in rat ventricular myocytes by propofol].

Whole-cell patch-clamp technique was applied to investigate the effect of propofol (25, 50 mumol/L) on transient outward potassium current (Ito) in rat ventricular myocytes. It was shown that the amplitude of Ito was decreased significantly after exposure to propofol. The effect is partially reversible after washing. At applied potential > or = 0 mV, statistical significant differences reached between propofol (25 and 50 mumol/L) group and the control group could be found. The voltage-dependent manner and the outward rectifier character were not affected by the drug at the two concentrations. It seems possible that the inhibition of potassium channels by propofol could underlie, at least in part, its beneficial effects in various cardiovascular diseases, including certain types of cardiac arrhythmia.

[Antiarrhythmic and antioxidative effects of intermittent hypoxia exposure on rat myocardium].

The purpose of the study was to observe the effects of intermittent hypoxia exposure (IH) on the arrhythmia and antioxidation with ligation of coronary artery of rat heart together with measuring SOD (superoxide dismutase) and MDA (malondialdehyde) in myocardium. Comparison with continued hypoxia exposure was also made. The results obtained are as follows. (1) Arrhythmia scores of ischemic arrhythmia and reperfusion arrhythmia observed in the rats treated with IH 28-day (IH28) and 42-day (IH42), one week (IH28-1W) and two weeks (IH28-2W) after 28-day IH, as well as in those with continued hypoxia 28-day (CH28) and 42-day (CH42), were significantly lower than controls. (2) SOD in IH28, IH42, CH28, CH42, IH28-1W, IH28-2W and three weeks after 28-day IH were significantly higher than controls; MDA in IH14, IH28, IH42, CH28, CH42, IH28-1W and IH28-2W were significantly lower than controls. It is suggested that IH for 28 or 42 days has some definite antiarrhythmic effect against ischemia and reperfusion, which was related to the strength of antioxidation in myocardium. The antiarrhythmic effects occurred gradually after 14 days IH and persisted for about two weeks after 28 days IH.

[The protective effect of MPEG-SOD on the function of left ventricle during acute hypoxia].

Monomethoxypolyethylene glycol (MPEG) was attached covalently to superoxide dismutase (SOD, EC1.15.1.1). The molecular weight of MPEG-SOD was about 7.0 x 10(5) Dalton determined by Fast Protein Liquid Chromatography (FPLC with Sepharose 6 HR10/30). MPEG-SOD exhibited a sharply enhanced serum half life (more than 30 h) than that of the native SOD (6-10 min). To determine the role of MPEG-SOD in acute hypoxia-induced injury of left ventricular function, heart rate (HR), arterial pressure (AP), left ventricular pressure (LVP) and dp/dt (LV +/- dp/dtmax) were measured in male SD rats divided into three groups: Control group (n = 8, intravenously injected with physiological saline), native SOD group (n = 8,800 U SOD i. v.) and MPEG-SOD group (n = 9,800 U MPEG-SOD i. v.). LVP, LV +/- dp/dtmax, AP and HR showed no significant difference among these three groups before hypoxia. But in acute hypoxia simulating altitude of 6,000-6,500 m, LVP, LV+dp/dtmax and AP were decreased in the control group, while in MPEG-SOD group they were all increased compared with those in control group (P < 0.05, P < 0.01). There were no significant difference between control group and native SOD group. The results indicate that MPEG-SOD has a protective effect on the injury of myocardial function induced by acute hypoxia, and suggest that acute hypoxia cause increase of superoxide free radical (O2.-) and other derivative radicals damaging membrane system of the cell.

[Effects of calcium blockers on the performance of left and right ventricles during acute hypoxia].

In anesthetized and thoracotomized 20 adult dogs under artificial respiration, the effects of calcium blockers (nifedipine, diltiazem and verapamil) on the mechanics of the left and right cardiac pumps under acute hypoxia were observed. The left and right ventricular pressure (LVP and RVP) and their dp/dt (+/- dp/dtmax), aortic flow (Fa), pulmonary pressure (Ppa) and heart rate (HR) were recorded. After treatment with calcium blockers, LVP and L +/- dp/dtmax decreased, and Fa increased, while RVP, R +/- dp/dtmax and Ppa all tended to increase. These results showed that the effects of calcium blockers on the performance of the left and right ventricles were different, suggesting that the dependence of left and right myocardium on calcium was different in degree. The mechanics of the left and right ventricles responded differently to calcium blockers under acute hypoxia. After treatment with calcium blockers, pressor responses on LVP by acute hypoxia disappeared. There was a great increase in Fa. Decrease in pressor response of RVP and Ppa was also observed in acute hypoxic dogs receiving verapamil and diltiazem. Comparing the effects of nifedipine, diltiazem and verapamil on the mechanics of the left and right cardiac pumps under acute hypoxia, it appears that diltiazem exerts beneficial effect on the performance of cardiac pump under acute hypoxia.

[Effects of intermittent hypoxia on transient outward current in rat ventricular myocytes].

To explore the ionic basis of the strengthening effect of intermittent hypoxic adaptation (IHA) on the electric stability of heart, the effects of intermittent hypoxia on the transient outward current (Ito) in rat ventricular myocytes were investigated by using whole-cell patch-clamp recording techniques. After 28-day (H28) exposure (6 h/d) to intermittent hypoxia, the density of Ito in the right, but not in the left, ventricular myocytes was dramatically increased as compared with the normoxia control (16.18 +/- 4.61 vs 6.32 +/- 1.35 pA/pF, P < 0.05), while the Ito density of the myocytes isolated from both sides of ventricles in 42-day-exposure group (H42) did not show significant difference. Except for a more negative shift of the steady-state inactivation curves (half-inactivation voltages: -38.9 +/- 2.3 vs -32.8 +/- 5.9 mV in the left ventricle and -41.9 +/- 4.5 vs -33.5 +/- 3.5 mV in the right ventricle) in the H42 group, all the other parameters for activation, inactivation and recovery kinetics of Ito of each group remained unchanged. It is speculated that the change in the current density of Ito may be responsible for the different hemodynamic responses of the ventricles to the early stage of hypoxia. The alteration in inactivation may participate in the cardioprotective effect of IHA.

Intermittent hypoxia exposure prevents mtDNA deletion and mitochondrial structure damage produced by ischemia/reperfusion injury.

In the present study, polymerase chain reaction (PCR) was conducted to determine mtDNA(4834) deletion, and myocardial ultrastructure was visualized by electron microscope to see whether intermittent hypoxia (high altitude) adaptation exerts some action on mitochondria against ischemia/reperfusion injury. Myocardial ischemia/reperfusion in isolated perfused rat hearts induced severe damage to the ultrastructure of myocardial mitochondria and mtDNA4834 deletion down to 87.5% of normoxia rats. After the rats were exposed to intermittent hypoxia (5000 m; 6 h/d for 28 d), the myocardial structure was well reserved and mtDNA(4834) deletion dropped to 28.57%of control (P<0.05). It is suggested that intermittent hypoxia adaptation prevents mtDNA deletion, and preserves normal structure of mitochondria, which would be beneficial to the maintenance of normal mitochondrial function, and increases tolerance of myocardium against ischemia/reperfusion injury.

[Study model for isolated heart perfusion combined with NMR technique].

Some improvements made to overcome the difficulty in the long distance perfusion, temperature maintenance, oxygen supply and the recollection of perfused fluid were described in our Langendorff perfusion in combination of NMR technique with which the rhythmic activity of isolated rat heart can be measured as long as 90 min.

Autocrine HBEGF expression promotes breast cancer intravasation, metastasis and macrophage-independent invasion in vivo.

Increased expression of HBEGF in estrogen receptor-negative breast tumors is correlated with enhanced metastasis to distant organ sites and more rapid disease recurrence upon removal of the primary tumor. Our previous work has demonstrated a paracrine loop between breast cancer cells and macrophages in which the tumor cells are capable of stimulating macrophages through the secretion of colony-stimulating factor-1 while the tumor-associated macrophages (TAMs), in turn, aid in tumor cell invasion by secreting epidermal growth factor. To determine how the autocrine expression of epidermal growth factor receptor (EGFR) ligands by carcinoma cells would affect this paracrine loop mechanism, and in particular whether tumor cell invasion depends on spatial ligand gradients generated by TAMs, we generated cell lines with increased HBEGF expression. We found that autocrine HBEGF expression enhanced in vivo intravasation and metastasis and resulted in a novel phenomenon in which macrophages were no longer required for in vivo invasion of breast cancer cells. In vitro studies revealed that expression of HBEGF enhanced invadopodium formation, thus providing a mechanism for cell autonomous invasion. The increased invadopodium formation was directly dependent on EGFR signaling, as demonstrated by a rapid decrease in invadopodia upon inhibition of autocrine HBEGF/EGFR signaling as well as inhibition of signaling downstream of EGFR activation. HBEGF expression also resulted in enhanced invadopodium function via upregulation of matrix metalloprotease 2 (MMP2) and MMP9 expression levels. We conclude that high levels of HBEGF expression can short-circuit the tumor cell/macrophage paracrine invasion loop, resulting in enhanced tumor invasion that is independent of macrophage signaling.

p21CIP1 mediates reciprocal switching between proliferation and invasion during metastasis.

Cell proliferation and invasion are critical for malignant progression, yet how these processes relate to each other and whether they regulate one another during metastasis is unknown. We show that invasiveness of breast cancer cells is associated with growth arrest due to p21CIP1 upregulation. Knockdown of p21CIP1 increases cell proliferation and suppresses invasion. Since p21CIP1 acts to inhibit cyclin E during cell-cycle progression, we demonstrated that a constitutively active form of cyclin E had similar effects to p21CIP1 inhibition resulting in enhanced cell growth and suppressed invasiveness. We tested these findings in vivo in the Polyoma middle T mammary tumor model in which p21CIP1 was deleted. p21CIP1 knockout mice exhibited dramatic suppression of metastasis, independent of tumor growth, which was rescued by p21CIP1. Metastasis suppression by p21CIP1 ablation was associated with striking cytoskeletal reorganization leading to a non-invasive and highly proliferative state. Thus, p21CIP1 regulates metastasis by mediating reciprocal switching between invasion and proliferation.

Phosphoinositide 3-kinase signaling is critical for ErbB3-driven breast cancer cell motility and metastasis.

Many malignancies show increased expression of the epidermal growth factor (EGF) receptor family member ErbB3 (HER3). ErbB3 binds heregulin ß-1 (HRGß1) and forms a heterodimer with other ErbB family members, such as ErbB2 (HER2) or EGF receptor (EGFR; HER1), enhancing phosphorylation of specific C-terminal tyrosine residues and activation of downstream signaling pathways. ErbB3 contains six YXXM motifs that bind the p85 subunit of phosphoinositide 3 (PI3)-kinase. Previous studies demonstrated that overexpression of ErbB3 in mammary tumor cells can significantly enhance chemotaxis to HRGß1 and overall metastatic potential. We tested the hypothesis that ErbB3-mediated PI3-kinase signaling is critical for heregulin-induced motility, and therefore crucial for ErbB3-mediated invasion, intravasation and metastasis. The tyrosines in the six YXXM motifs on the ErbB3 C-terminus were replaced with phenylalanine. In contrast to overexpression of the wild-type ErbB3, overexpression of the mutant ErbB3 did not enhance chemotaxis towards HRGß1 in vitro or in vivo. We also observed reduced tumor cell motility in the primary tumor by multiphoton microscopy, as well as a dramatically reduced ability of these cells to cross the endothelium and intravasate into the circulation. Moreover, whereas mutation of the ErbB3 C-terminus had no effect on tumor growth, it had a dramatic effect on spontaneous metastatic potential. Treatment with the PI3-kinase inhibitor PIK-75 similarly inhibited motility and invasion in vitro and in vivo. Our results indicate that stimulation of the early metastatic steps of motility and invasion by ErbB3 requires activation of the PI3-kinase pathway by the ErbB3 receptor.