Effects of chloride replacement and chloride transport blockade on the tonic tension of frog atrial trabeculae

The effects of a chloride-poor medium (methanesulfonate substituted) and a chloride transport inhibitor (SITS) on the outward delayed current and the tonic tension were studied on frog atrial trabeculae under voltage-clamp conditions. The outward delayed current decreased in low-chloride medium (10.5 mmol/l) or in the presence of SITS (2 mmol/l). The tonic tension increased in chloride-poor solution and decreased following SITS. The replacement of chloride by methanesulfonate enhanced the transient increase of tonic tension induced by low external sodium concentration while SITS reduced it. In the same conditions, the effect of the chloride-poor medium was abolished in the presence of SITS. The results showing an increase in Na-Ca exchange in low-chloride medium and a decrease by SITS are discussed assuming that changes in the inner negative charge density influenced the Na-Ca exchange mechanism; the influence of pHi variation are also considered.     

Effects of manganese chloride on the outward currents in frog atrial trabeculae

The effects of MnCl2 on outward currents in frog atrial muscle were investigated under voltage-clamp conditions. MnCl2 (3 mmol/L), which completely abolished the slow inward current, produced a decrease in the outward background current (Ib) at potentials positive to -50 mV. The delayed outward current (Ix, time dependent) was not altered by Mn. "Isochronic activation curves" for Ix and decay of current tails at -40 mV remained unaffected after Mn. Effects on Ib probably reflect a decrease in IK1 related to the decrease in Ca influx as well as a reduction in the Na-Ca exchange current.     

Tension development of normal and hypertrophied-failing papillary muscles following rapid stimulation

Recent studies have shown that numerous cellular alterations exist in hypertrophied-failing (HF) cardiac muscle. Of particular interest is the finding of an altered ability of the Na-K pump to regulate membrane potential in this tissue during periods of transient stimulation. The present study was designed to determine if this altered Na-K pump function is in any way related to the ability of this tissue to develop force. Along these lines the rate of stimulation (6/min) of normal and hypertrophied-failing right ventricular papillary muscles from cats was increased to 60/min for 90 sec. This procedure was repeated in solutions with low Na+, low Na+ and Ca++, and Ouabain. These solutions were utilized to vary the ionic load on the Na-K pump and the Na-Ca exchanger. The results demonstrate that the pattern of changes in tension in HF papillary muscles seen following periods of rapid stimulation are significantly different from those of normal muscles. The pattern of changes in mechanical performance were found to be similar to the membrane potential changes described in previous studies. In addition, lowering the Na+ load presented to HF muscles returned the characteristic pattern of changes in tension, following drive, toward normal. Ouabain was found to inhibit the changes in tension development following increased rates of stimulation that are thought to be produced by activation of the Na-K pump. The results suggest that the ability of the Na-K pump to maintain normal transmembrane ionic gradients may be altered in HF muscles. This alteration appears to be capable of affecting cellular Ca++ possibly through the Na-Ca exchange system.     

Effect of reduced Na gradient on electrical activity in isolated bovine and feline ventricular myocytes

We have studied changes in electrical activity resulting from abrupt alterations of the Na gradient, using ventricular myocytes isolated from feline and bovine hearts. Attempting to investigate the ionic current possibly generated by Na-Ca exchange, we studied the effects of the changes in [Na]o in the presence of 20 mM CsCl to inhibit K currents. To facilitate the effect of Cs, we also used a K-free solution and a patch electrode filled with 150 mM cesium glutamate. The application of 20 mM Nao resulted in hyperpolarization and the action potential duration was reduced. Under voltage clamp, 20 of 45 mM Nao generated an outward current at all membrane potentials investigated. The initial part (100-200 ms) of this current was only partially inhibited by 5 mM NiCl2 which is known to fully block the Ca inward current. However, the outward current generated by the reduced [Na]o was fully inhibited by 20 mM MnCl2 (which presumably inhibits Na-Ca exchange). Our observations extend the work on multicellular cardiac preparations indicating that the outward current elicited by a sudden decrease in Na gradient could be generated by Na-Ca exchange. Although the characteristics of this outward current support certain concepts of the Na-Ca exchange in cardiac muscle, we cannot at present exclude a contribution of other membrane current(s).     

Single and multiple early afterdepolarization caused by nickel in rat atrial muscle

We examined the possible role of the Na-Ca exchange (NCX) in the arrhythmogenesis in rat atrial preparations applying microelectrode technique. In control Tyrode solution preparations isolated from the sinoatrial area contracted with frequency of 48+/-4 min(-1) (group I) or 84+/-7 min(-1) (group II). In preparation beating with low frequency partial inhibition of NCX by administration of Ni2+ (0.3 mmol/l) to the bath solution caused single early afterdepolarization (EAD) on the 15th min. During the following five minutes they were transformed into multiple EADs from 4 to 47 (action potentials) with general duration of 1-12 s. The effects were reversible. Ni2+ (0.3 mmol/l) in the preparations beating with higher rate (group II) did not cause multiple EADs, but after higher Ni2+ concentration (0.5 mmol/l) single EAD was observed more often. It was concluded that Ca2+ overload due to partial block of the NCX can contribute to the development of atrial tachyarrhythmias.     

Na超负荷与Na／H交换的关系—在等容收缩离体大鼠心脏...

Thirty min after stabilization perfusion with oxygenated buffer, hearts were divided in four groups: (1) Control group: 75 min. of aerobic perfusion; (2) Low flow anoxia group: 45 min. of low flow anoxic perfusion (95% N2:5%CO2, 0.15 ml/min.) followed by 30 min. of aerobic perfusion; (3) Ouabain group: protocol same as (2), except that ouabain (200 mumol/L) was added to anoxic perfusate during low flow anoxia; (4) Ouabain+Amiloride group: protocol same as (3) except that amiloride (0.5 mmol/I) was added to perfusate during low flow anoxia. Compared with the low flow anoxia group, ouabain resulted in an additional increase in Na during reperfusion accompanied with a depressed ventricular function. The deleterious effects of ouabain could be significantly combatted by amiloride. It is concluded that a decrease in Na/K ATPase activity may contribute to Na gain in reperfused myocardium, the mechanism of which might result from stimulation of Na/H exchange.     

Effect of potassium ions and membrane potential on the Na-Ca-K exchanger in isolated intact bovine rod outer segments

Two recent studies reported that Na-Ca exchange in the outer segments of tiger salamander rod photoreceptors (Cervetto, L., Lagnado, L., Perry, R. J., Robinson, D. W., and McNaughton, P. A. (1989) Nature 337, 740-743) and of bovine rod photoreceptors (Schnetkamp, P. P. M., Basu, D. K., and Szerencsei, R. T. (1989) Am. J. Physiol. 257, C153-157) requires and transports K+ in a 4Na/(1Ca+1K) stoichiometry. In this study, we have examined the effects of K+ ions and membrane potential on the kinetics of Na-Ca and Ca-Ca exchange in rod outer segments isolated from bovine retinas. The objective was to establish the ion selectivity and voltage dependence of the different cation binding sites on the Na-Ca-K exchange protein. Potassium ions activated Na-Ca exchange when present on the Ca2+ side, although the extent of activation decreased with decreasing Na+ concentration. Potassium ions inhibited Na-Ca exchange when present on the Na+ side; inhibition arose from competition between Na+ and K+ for a common single cation-binding site. Activation of Na-Ca exchange by K+ displayed a different ion selectivity than that observed for inhibition of Na-Ca exchange by K+. The results are interpreted in terms of a three-site model for the rod Na-Ca-K exchanger. The rate of forward Na-Ca exchange decreased by 1.75-fold for a 60 mV depolarization of the plasma membrane but only at lower Na+ concentrations. The rate of Ca-Ca exchange was not affected by changes in membrane potential.     

NaCl抑制棉花幼苗生长的机理—盐离子效应

75和150 mmol/L NaCl处理.降低棉花幼苗叶面积、叶相对扩展率,蒸腾和木质部汁液K~ 浓度;而增大叶细胞质膜透性、渗透势、叶Na~ 含量和木质部汁液Na~ 和Cl~-的浓度。生长在75mmol/L NaCl加压(根际)和不加压条件下的棉花,叶面积、叶相对扩展率、蒸腾、叶质膜透性和渗透势的变化基本一样。这些结果表明棉花幼苗的拒盐能力不大,盐害的原因是盐的原初效应,而不是盐的次生效应。另外,盐对棉花幼苗叶相对扩展率和质膜透性的效应在生长后期降低,表明棉花幼苗也具有一定的耐盐能力。     

Effects of S-nitroso-N-acetyl-penicillamine administration on glucose tolerance and plasma levels of insulin and glucagon in the dog.

It has been suggested that nitric oxide (NO, nitrogen monoxide) is a regulator of carbohydrate metabolism in skeletal muscle. The present study was undertaken to investigate the acute effects of the nitric oxide donor S-nitroso-N-acetylpenicillamine (SNAP) on blood glucose levels and on the gluco-regulatory hormones insulin and glucagon in healthy dogs. The acute effects of SNAP on mean arterial pressure and heart rate were also investigated. The drug was administered intravenously and the pre- and postprandial blood glucose, plasma insulin, and glucagon concentrations were determined at half-hour time intervals postadministration after a glucose challenge. The plasma nitrate and nitrite concentrations were measured and taken as the biochemical markers of in vivo NO formation. The oral glucose tolerance test revealed an impaired glucose tolerance in SNAP-treated dogs as reflected by the area under the glucose curve, 1150.50 +/- 63.00 mmol x 150 min and 1355.25 +/- 102.01 mmol/L x 150 min in dogs treated with 10 and 20 mg/kg of SNAP, respectively, compared with 860.25 +/- 60.68 mmol/L x 150 min in captopril-treated controls (P < 0.05). The 2-h blood glucose concentration in dogs treated with 20 mg/kg body wt of SNAP was 9.17 +/- 1.10 mmol/L compared with 5.59 +/- 0.26 mmol/L for captopril-treated controls (P = 0.015). The oral glucose tolerance test also confirmed an impaired insulin secretion in the SNAP-treated dogs. While the plasma insulin concentration increased gradually in the captopril-treated controls to a peak value of 39.50 +/- 2.55 microIU/ml, 1.5 h after a glucose challenge there was a decrease in the plasma insulin concentration in SNAP-treated dogs to a low value of 20.67 +/- 0.88 microIU/ml (P = 0.006). In contrast, there were no significant differences in plasma glucagon concentration in SNAP-treated dogs and captopril-treated dogs at any time points. Using the Griess reaction, we found that there was a 27-95% increase in plasma nitrate/nitrite concentration on administration of SNAP. The sustained hyperglycemic effect observed in SNAP-treated dogs was accompanied by a marginal decrease in the mean arterial blood pressure and a significant increase in heart rate (P < 0.05). We conclude that acute administration of SNAP in the oral glucose tolerance test releases NO that modulates the parameters of carbohydrate metabolism.     

Functional origin of rate-induced changes in atrioventricular nodal conduction time of premature beats in the rabbit

The characteristics and origin of the rate-induced changes in atrioventricular nodal conduction time of premature beats (A2H2 intervals) were studied in isolated rabbit heart preparations. Increasing the basic driving rate during a periodic premature stimulation prolonged (a net inhibitory effect) and shortened (a net facilitatory effect) significantly (p less than 0.01, n = 17) the A2H2 intervals associated with long and short recovery times (H1A2 intervals), respectively. The origin of these responses was sought for by analyzing interactions between facilitation and fatigue. When the fatigue developed at a fast basic rate was estimated from changes in conduction time of basic beats and subtracted from the corresponding A2H2 intervals, the calculated A2H2 intervals showed enhanced facilitation but no fatigue. When independently obtained fatigue and facilitation effects were added to the control A2H2 intervals for corresponding H1A2 intervals, resulting A2H2 intervals correlated strongly with the ones observed at the equivalent fast basic rate (r = 0.99, p less than 0.001). Moreover, changes in the A2H2 intervals of premature beats tested with constant coupling intervals during 5-min fast rates were biphasic, confirming the overlapping and competition between facilitation and fatigue effects. Hence, rate-induced deviations of premature nodal conduction time from that predicted by changes in recovery time are consistent and result from the interaction between the overlapping effects produced by two independent, antagonist, and dynamically distinct nodal properties (facilitation and fatigue).     

硫对烟草叶片光合特性和叶绿素荧光参数的影响

通过液培试验,测定了不同硫营养水平(0～32 mmol/L)下烟草叶片的叶绿素含量、气体交换参数和叶绿素荧光参数.结果表明,随着硫浓度的升高,烟草叶片的Chl.a、Chl.b、总Chl的含量和Chl.a/b逐渐增加;类胡萝卜素呈先下降后升高的趋势;烟草叶片的净光合速率(Pn)、蒸腾速率(Tr)、气孔导度(Gs)、胞间CO2浓度(Ci)下降显著,气孔限制值(Ls)明显升高,这表明高硫对烟草叶片的气体交换参数影响较大.随着硫浓度的升高,烟草叶片光合有效量子产量(EQY)、光合电子传递速率(ETR)、光化学淬灭(qP)都表现为先升高后降低,一般是4 mmol/L和8 mmol/L处理相对较高,浓度超过8 mmol/L以后,以上参数显著下降.非光化学淬灭(NPQ) 0,16 mmol/L和32 mmol/L处理表现相对较高,2、4、8 mmol/L处理的相对较低,2～8 mmol/L浓度的处理最适宜烟草的生长,高硫或低硫都会导致烟草EQY、ETR、qP降低和NPQ的升高.     

Possible role of Na+ ions in intracellular Ca2+ release in frog auricular trabeculae

Membrane potential-current and mechanical tension of frog atrial muscle were studied in a Ca and Mg-free solution containing 1 mmol/l EGTA (Ca-free solution). Exposure to Ca-free solution resulted in a shortening of action potential duration within 1.5 min and a subsequent lengthening which were paralleled by changes in magnitude and duration of the contraction. Similarly, the slow inward current quickly disappeared and progressively reappeared with a quite slower inactivation time-course. Its reversal potential varied with [Na]0 as for a pure Na current. By 12 min in Ca-free solution, the tension-voltage relation could be interpreted as the sum of two components correlated with the slow inward current and the membrane potential respectively. Contractures in response to sustained large depolarizations had similar time courses in Ca-free solution and Ringer's containing Na-Ca exchange blockers (Mn2+ 15 mmol/l or La3+ 3 mmol/l). Intracellular Na loading by voltage-clamp depolarizations (40 mV from the resting potential for 100 ms, at 0.2 Hz) in the presence of Veratrine (7.5 X 10(-6) g/ml) caused a large progressive increase in tonic tension. An intracellular Ca2+ release is invoked, partly related to Na+ entry and partly to membrane potential changes. The potential dependent part could be influenced by intracellular Na+.     

RP-HPLC测定红丝线提取物中紫蓝素的含量

建立了红丝线提取物中紫蓝素的测定方法。采用反相高效液相色谱法,色谱柱为ZORBAXXDB-C18(4.6mm×150mm,5μm);流动相:V(乙腈):V[75mmol/L乙酸铵+0.5mmol/LEGTA(pH7.0)]=8∶92;流速:1mL/min;检测波长590nm。紫蓝素的线性范围为2.5～50mg/L(r=0.9999),回收率97.9%～101.5%。该法简便、准确,重复性好,适用于测定红丝线提取物中紫蓝素的含量。     

Electrical and mechanical activity of isoproterenol-damaged frog heart

The electrical and mechanical activities of myocardial strips from Rana pipiens were studied in the steady state at various stimulation frequencies and after a period of rest. The temperature of the bath was varied between + 12 and 35 degrees C. Normal myocardium was compared with that damaged by isoproterenol (ISO). The percentage change of action potential durations (APD50) and isometric force (P) was similar in ISO-damaged and control hearts at various bath temperatures with steady state stimulation rates between 20 and 100/min. At low stimulation rates (3-6/min) the prolongation of the action potential (AP) was more pronounced and the P-decrease was less in ISO-damaged myocardium compared to controls. These differences became more apparent at low bath temperatures. After 10 min of rest, APD50-90 was significantly prolonged in ISO-damaged heart and P was increased by a factor of 2 compared to controls (stimulation rate 20/min). Steady state values, on the other hand, were nearly the same in both groups. These findings are interpreted as indicating a temperature or ISO-dependent increase of electrogenic trans-sarcolemmal Ca2+-uptake during low frequency, or post-rest stimulation, either directly by an increase of the slow inward current (Isi), or indirectly by decreased K+-permeabilities.     

Positive inotropic effects of ouabain in isolated cat ventricular myocytes in sodium-free conditions

The inotropic and toxic effects of cardiac steroids are thought to result from Na(+)-K(+)-ATPase inhibition, with elevated intracellular Na(+)(Na)causing increased intracellular Ca(2+)(Ca) via Na-Ca exchange. We studied the effects of ouabain on cat ventricular myocytes in Na(+)-free conditions where the exchanger is inhibited. Cell shortening and Ca transients (with fluo 4-AM fluorescence) were measured under voltage clamp during exposure to Na(+)-free solutions [LiCl or N-methyl-D-glucamine (NMDG) replacement]. Ouabain enhanced contractility by 121 +/- 55% at 1 micromol/l (n = 11) and 476 +/- 159% at 3 micromol/l (n = 8) (means +/- SE). Ca transient amplitude was also increased. The inotropic effects of ouabain were retained even after pretreatment with saxitoxin (5 micromol/l) or changing the holding potential to -40 mV (to inactivate Na(+) current). Similar results were obtained with both Li(+) and NMDG replacement and in the absence of external K(+), indicating that ouabain produced positive inotropy in the absence of functional Na-Ca exchange and Na(+)-K(+)-ATPase activity. In contrast, ouabain had no inotropic response in rat ventricular myocytes (10-100 micromol/l). Finally, ouabain reversibly increased Ca(2+) overload toxicity by accelerating the rate of spontaneous aftercontractions (n = 13). These results suggest that the cellular effects of ouabain on the heart may include actions independent of Na(+)-K(+)-ATPase inhibition, Na-Ca exchange, and changes in Na.     

NaCl胁迫对唐古特白刺愈伤组织的生理效应

以唐古特白刺(Nitraria tangutorum Bobr.)愈伤组织为材料,研究低(75 mmol/L)、中(150 mmol/L)、高(300 mmol/L)浓度NaCl处理下其膜脂过氧化、抗氧化酶活性及渗透性调节物含量的变化,试图从细胞水平揭示唐古特白刺适应盐环境的生理机制。结果显示:(1)唐古特白刺愈伤组织中MDA含量在低浓度NaCl处理下与对照无显著性差异,而在中高浓度下显著升高。(2)白刺愈伤组织超氧化物歧化酶(SOD)活性在各浓度NaCl胁迫下均比对照显著升高,且此效应无浓度依赖性;其过氧化氢酶(CAT)活性随胁迫浓度的增加呈先升高后降低的变化趋势,在中低浓度下比对照显著增加,高浓度下显著降低为对照的64%;其过氧化物酶(POD)活性在低浓度下无显著性变化,在中高浓度显著下降为对照的55%和29%。(3)随NaCl胁迫浓度的增加,白刺愈伤组织中脯氨酸、可溶性糖和可溶性蛋白含量均呈先升高后降低的变化趋势,且除高浓度下可溶性蛋白含量约降为对照的87%外,其余NaCl胁迫处理的3种渗透调节物含量均高于对照。研究发现,白刺愈伤组织在低浓度的盐胁迫下具有较强的抗氧化酶活性和渗透性调节作用,因而表现出较强的抗氧化作用,但高浓度NaCl胁迫对白刺愈伤组织造成了显著的氧化损害。     

赤豆子叶β-半乳糖苷酶的纯化及其性质的研究

β-半乳糖苷酶 ( EC3.2 .1 .2 )广泛存在于动植物的组织中 ,如在杏仁、桃子、大豆、咖啡豆等植物 ,蜗牛 ,哺乳动物的肠道中都有 β-半乳糖苷酶 .同样 ,微生物也能产生β-半乳糖苷酶 ,俗称乳糖酶 .乳糖操纵子学说的提出就是建立在对微生物β-半乳糖苷酶研究基础之上的 .在过去的研究中 ,关于微生物、动物来源的乳糖酶报道较多[1] ,而对于植物来源的β-半乳糖苷酶研究报道却相对较少[2 ] .它可能降解多糖中 β-构型半乳糖苷键 ,为种子生长发育提供必要的能量来源 .但目前对β-半乳糖苷酶在植物中确切的生理生化功能尚不清楚 .为了进一步阐明…     

绵羊心浦肯野纤维d-受体和β-受体激动时离子流Isi和Ix的变化

当绵羊心浦肯野纤维α-和β-受体分别激动时,用双微电极法电压箝制术研究慢内向离子流Isi和延迟整流外向离子流Ix的变化。心得安阻断β-受体时,苯肾上腺素5.0×10~(-6)mol/L使Isi的峰值由17.5增加到26nA(n=6,P<0.05).并使Isi由失活到完全恢复的时间由293±51ms延长到441±109ms(n=4,P<0.05),但对Ix无明显影响。酚妥拉明阻断α-受体时,异丙肾上腺素4×10~(-7)mol/L使Isi峰值由27.7增加到40.8nA(n=7,P<0.05),对Isi的动力过程无明显影响,却使Ix尾电流的幅值由6.7增加到14,4nA(n=6,P<0.05)。表明α-和β-受体激动剂作用的差异在于对延迟整流离子流的影响不同。     

Mehler反应在大豆叶片耗散过剩光能中的作用

从初花期大豆植株茎基部引入不同浓度碘乙酰胺(iodoacetamide,IA),叶片光合速率(Pn)受到不同程度的抑制,2h强光照射后抑制效应更加明显,O