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.

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.

Stimulation by melittin of Na+-Ca2+ exchange current in ventricular myocytes of guinea pigs.

AIM: To study the mechanism of calcium overload induced by melittin in myocytes. METHODS: Whole cell patch-clamp technique was applied for recording the currents. RESULTS: Mel 0.05, 0.1 micromol/L increased the peak amplitude of I(Na) (nA) from -2.1+/-0.8 to -3.2+/-1.0 (n=7, P < 0.05) and -3.7+/-1.5 (n=7, P < 0.05) respectively at testing potential of -40 mV. Mel 0.05, 0.1, 0.2 micromol/L had no significant effect on I(Ca), but enhanced I(Na-Ca) (pA) from 53+/-21 to 427+/-256 (n=5, P < 0.05), 349+/-147 (n=5, P<0.01) and 320+/-97 (n=5, P < 0.05) respectively at a testing potential of +50 mV. CONCLUSION: The stimulating effect of Mel on I(Na-Ca) rather than the effect on I(Ca) contributes to the calcium overload of myocytes.

[The effect of hypoxic preconditioning on myocardium energy metabolism].

AIM AND METHODS: To evaluate the protective effects of hypoxic preconditioning (HPC) on myocardial energy metabolism, Langendorff-perfused hearts, exposed to HPC, were subjected to hypoxia/reoxygenation (5/10 min). 31P NMR was used to sequentially follow the time courses of high energy phosphates (HEP) contents and intracellular pH (pHi) of the rat myocardium. RESULTS: The Contents of Phosphocreatine (PCr), Adenosine Triphosphate (ATP) and the PCr/Pi (inorganic phosphate) ratios decreased during 30 min hypoxia, but the reduction was slower for the HPC group compared with Control. Reoxygenation induced recovery of myocardial HEP in both groups, HPC enhanced t he recovery especially in initial stage o f reoxygenation. However, pHi change was not significant for HPC group in this experiment. CONCLUSION: HPC improves the myocardial energy metabolism level during prolonged hypoxia and subsequent reoxygenation and protects myocardium against hypoxia/reoxygenation injury.

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.

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.

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.

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.

[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.

Estradiol potentiates antiarrhythmic and antioxidative effects of intermittent hypoxic rat heart.

AIM: To study the effects of estradiol (Est) on antiarrhythmic and antioxidative effects of intermittent hypoxia in rat heart. METHODS: Ligating and loosening the coronary artery of rat to induce ischemic and reperfusion arrhythmias, using arrhythmia score (AS) to evaluate the arrhythmias, measuring the activity of superoxide dismutase (SOD) and the content of malondialdehyde (MDA) in myocardium. RESULTS: AS of arrhythmia induced by ischemia and reperfusion in intermittent hypoxia 28-d group (IH28) and in intermittent hypoxia with Est group (IH14-Est) are lower than that in control group (CON), respectively. AS of ischemic arrhythmia but not reperfusion arrhythmia in Est treated group (ESTG) was lower than that in CON. No significant difference in AS of ischemia and reperfusion existed among CON, vehicle group (VEH), and intermittent hypoxia 14-d group (IH14). The activity of SOD was higher and the content of MDA was lower in IH28 and in IH14-Est compared with that in CON. No significant difference of the activity of SOD and the content of MDA existed among CON, VEH, IH14, and ESTG. CONCLUSION: Est potentiated the antiarrhythmic and antioxidative effects of intermittent hypoxia on rat heart.

Volume- and calcium-activated chloride channels in human umbilical vein endothelial cells.

AIM: To characterize the properties of chloride currents and its modulation in human umbilical vein endothelial cells (HUVEC). METHODS: Using whole-cell patch-clamp recording techniques. RESULTS: Exposure of HUVEC to 13.5% and 27% hypotonic solution (HTS) induced a current ICl, vol. This current was correlated with the changes in cell volume and showed a modest outward rectification. It was slowly inactivated at positive potential (> 50 mV), and it was time- and voltage-independent in kinetics. The current densities (pA/pF) were 20 +/- 3 (13.5% HTS) and 58 +/- 4 (27% HTS, n = 7), respectively at +100 mV test potential. Applying GTP gamma s (300 mumol.L-1) elicited a current similar to ICl, vol, while cAMP (0.5 mmol.L-1) had no effect on the current. Increase in [Ca2+]i, either by directly loading cells with high concentration of Ca2+ (CaCl2), or by perfusing vasoactive agonist ATP (10 mumol.L-1), activated ICl, Ca. The current density was only (23 +/- 5) pA/pF (n = 8 cells). Such current was slowly activated at positive potential, inactivated quickly at negative potential, and showed strong outward rectification. Both currents were inhibited by DIDS and verapamil. Challenging a cell with elevated [Ca2+]i and HTS activated ICl, vol on the top of ICl, Ca in the same cell, suggested co-existence of these two currents and that they were modulated by different ways. cAMP-regulated chloride channel and ClC (chloride channel family) channel were absent. CONCLUSION: HUVEC express two kinds of chloride channels, ICl, vol activated by change in cell volume and ICl, Ca by elevation of [Ca2+]i, respectively.

Intermittent hypoxia exposure-induced heat-shock protein 70 expression increases resistance of rat heart to ischemic injury.

AIM: To quantify the levels of HSP70 induced by different durations of intermittent (high altitude) hypoxia and to correlate them with the degree of protection of the rat heart from ischemic injury. METHODS: Reverse transcriptase polymerase chain reaction (RT-PCR) was used to detect the level of HSP70 mRNA expression in rat myocardium. Ischemia/reperfusion injury was presented as severity of arrhythmias induced by occlusion and reperfusion of the left anterior descending coronary artery of rat heart. RESULTS: The level of HSP70 mRNA expression increased progressively along with the duration of intermittent hypoxia training. It was 2.6, 3.6, and 3.8 folds after 14-, 28-, and 42-d exposures compared to that of normoxia. The tolerance of rat heart to ischemia/reperfusion injury increased with hypoxia pretreatment. Such an effect was significant after rat were exposed to a 28-d intermittent hypoxia (IH). The scores for ischemia and reperfusion inducing arrhythmia for 28- and 42-d IH were 1.2 +/- 0.5, 1.0 +/- 0.5 and 1.0 +/- 0.5, 0.9 +/- 0.5 (P < 0.01 compared with 4.0 +/- 0.7, 3.3 +/- 0.6 in normoxia rats). The overexpression of HSP70 and the increased tolerance to subsequent acute ischemia/reperfusion injury could last for 2 wk after the rats (subjected to 28 d IH) returned to normoxia. Furthermore, there was a reverse correlation between the amount of HSP70 induced and the arrhythmia occurrence (r = -0.98, -0.92 for ischemia and reperfusion induced arrhythmia, P < 0.01). CONCLUSION: These results suggest that increased resistance of rat heart to ischemia/reperfusion injury after intermittent hypoxia exposure may be related to the amount of HSP70 induced.

Inhibitory effect of 1-(2, 6-dimethylphenoxy)-2-(3, 4-dimethoxyphenyl-ethylamino) propane hydrochloride on inward rectifier and delayed rectifier K+ currents in guinea pig ventricular myocytes.

AIM: To study the effects of 1-(2,6-dimethylphenoxy)-2-(3,4-dimethoxyphenyl-ethylamino) propane hydrochloride (DDPH) on action potential (AP), inward rectifier K+ current (IK1), and delayed rectifier K+ current (IK) in isolated guinea pig ventricular myocytes. METHODS: Whole cell patch-clamp recording techniques. RESULTS: DDPH 0.1-100 mumol.L-1 decreased 50% duration of action potential (APD50) concentration-dependently. APD50 was shortened from (493 +/- 58) to (262 +/- 38) ms (n = 7 cells from 5 guinea pigs, P < 0.01) by DDPH 10 mumol.L-1. However, 90% duration of action potential (APD90) was increased by DDPH (> 1 mumol.L-1). At high concentration (> 10 mumol.L-1) DDPH decreased resting membrane potential (RP) and amplitude of action potential (APA). DDPH inhibited tail current of IK (IK.tail) concentration-dependently, 46% at 10 mumol.L-1 and 78% at 100 mumol.L-1. EC50 for DDPH inhibiting IK was 13.3 (11.6-16.7) mumol.L-1. DDPH also blocked IK1. DDPH at high concentration (> 10 mumol.L-1) shifted the reverse potential of IK1 positively. All the effects of DDPH were reversible after washout. CONCLUSION: DDPH blocked both IK1 and IK current in guinea pig ventricular myocytes.

Hypoxic preconditioning upregulates KATP channels through activation of protein kinase C in rat ventricular myocytes.

AIM: To test: 1) if hypoxic preconditioning upregulates the activity of KATP channels in isolated adult rat cardiac myocytes; 2) if the upregulation involves protein kinase C (PKC). METHODS: By the whole-cell patch-clamp recording technique, KATP channel currents (IKATP) were measured in the cardiomyocytes with no pretreatment (CON), hypoxic exposure preceding reoxygenation (HPC), phorbol 12-myristate 13-acetate (PMA), and chelerythrine addition with HPC (CH + HPC), respectively. RESULTS: At 0 mV and 5 min after 2, 4-dinitrophenol (DNP) perfusion, the membrane currents for the CON, HPC, PMA, and CH + HPC were (3.5 +/- 1.9), (7.7 +/- 1.5), (7.5 +/- 3.3), (4.6 +/- 2.4) nA, respectively. Compared with the CON, the IKATP in the HPC and PMA were significantly augmented (P < 0.01) while the IKATP in the CH + HPC remained similar to the CON (P > 0.05). CONCLUSION: 1) hypoxic preconditioning stimulated the activity of PKC and markedly enhanced the activity of KATP channels in the isolated rat cardiac myocytes; 2) PKC activation was involved in the upregulation of KATP channels.

Inhibitory effects of dauricine on potassium currents in guinea pig ventricular myocytes.

AIM: To study the effects of dauricine(Dau) on the rapidly activating component (IKr), the slowly activating component (IKs) of the delayed rectifier potassium current, and the inward rectifier potassium current (IKl) in guinea pig ventricular myocytes. METHODS: Single myocytes were dissociated by enzymatic dissociation method. The currents were recorded with the whole-cell configuration of the patch-clamp technique. RESULTS: (1) Dau 1, 3, 10, 30, and 100 mumol.L-1 blocked IKr and tail current (IKr-tail) in a concentration-dependent manner. The IC50 for block of IKr-tail was 16 (95% confidence limits: 13-22) mumol.L-1. The time constant of IKr-tail deactivation was (140 +/- 38) ms in the control and (130 +/- 26) ms in the presence of Dau 30 mumol.L-1 (n = 6 cells from 3 animals, P > 0.05). (2) Dau 1-100 mumol.L-1 produced concentration-dependent blocks of IKs and tail current (IKs-tail). The IC50 value for block of IKs-tail was 33 (95% confidence limits: 24-46) mumol.L-1. The time constant of IKs-tail deactivation was (92 +/- 18) ms in the control and (84 +/- 16) ms in the presence of Dau 30 mumol.L-1 (n = 8 cells from 4 animals, P > 0.05). (3) Addition of Dau 30 mumol.L-1 induced block of IKs and IKs-tail (n = 7 cells from 3 animals). The degree of block of IKs and IKs-tail depended on test potentials, increasing with more positive depolarizations. (4) Dau 20 mumol.L-1 blocked mainly inward component of IKl and reduced the reversal potential from -72 mV (control) to -78 mV (n = 6 cells from 3 animals). CONCLUSION: (1) Dau inhibited IKs, but not the process of IKs deactivation. (2) Dau blocked IKr, but not the process of deactivation. (3) Dau had a blocking effect on IKl.

[The studies on protective effects of SM against myocardial hypoxia/reoxygenation injury].

AIM AND METHODS: To assess the myocardial effects of Salvia Miltiorrhiza (SM) injection against hypoxia-reoxygenation injury, 31P NMR was used to trace the time courses of high energy phosphates (HEP) content and intracellular pH (pHi) of the isolated perfused rat hearts under hypoxia (30 min) and subsequent reoxygenation (40 min). RESULTS: It was discovered that SM significantly preven-ted the decrease in the myocardial HEP content during hypoxia, enhanced the recovery of myocardial phosphocreatine (PCr), adenosine triphosphate (ATP) and the PCr/Pi (inorganic phosphate) ratios during reoxygenation, and lightened the decrease of the myocardial pHi value caused by hypoxia. CONCLUSION: SM improves the myocardial energy metabolism level during prolonged hypoxia and subsequent reoxygenation and protects myocardium against hypoxia/reoxygenation injury. SM significantly attenuates acidosis during hypoxia and prevents the appearance of very acidic areas of the myocardium after reoxygenation.

[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.

Inhibitory effects of estradiol on inward rectifier and delayed rectifier K+ currents in guinea pig ventricular myocytes.

AIM: To study the effects of estradiol (Est) on inward rectifier K+ (IK1) and delayed rectifier K+ (IK) channels in isolated guinea pig ventricular myocytes. METHODS: Using whole cell patch-clamp recording techniques. RESULTS: Est 10 mumol.L-1 and 100 mumol.L-1 decreased the action potential duration, APD50, from (474 +/- 71) ms to (330 +/- 75) ms and (229 +/- 67) ms (n = 7 cells of 7 guinea pigs, P < 0.05), respectively. Est 100 mumol.L-1 also decreased APD90 from (587 +/- 60) ms to (418 +/- 79) ms (n = 7, P < 0.05). Est inhibited IK tail current (IK.tail) concentration-dependently. IK.tail was depressed 53% (n = 5, P < 0.05) at 10 mumol.L-1 and 80% (n = 5, P < 0.01) at 100 mumol.L-1 compared with control. Est > or = 10 mumol.L-1 blocked IK1. The maximal inhibition of inward current of IK1 occurred at -100 mV test potential was 49% (n = 5, P < 0.01) and outward current of IK1 at -40 mV was 72% (n = 5, P < 0.01). The reverse potential shifted negatively, from -70 to -76 mV. CONCLUSION: Est possessed blocking effects on both IK1 and IK channels in guinea pig ventricular myocytes.