二氮嗪两种应用对豚鼠缺血再灌注心肌电生理特性的影响

目的：观察二氮嗪两种应用方式对缺血再灌注豚鼠心室乳头肌细胞电生理特性的影响。方法: 24只豚鼠随机分为对照组、实验组、预先给药组(各组8只)，取离体左室乳头肌标本。对照组37 ℃充氧台氏液平衡灌流80 min后，用4 ℃ St.Thommas液灌流停搏30 min，再行充氧台氏液复灌60 min。实验组除4 ℃ St.Thommas液含二氮嗪(100 μmol/L)外余步骤同对照组。预先给药组仅在平衡灌流60 min后改用二氮嗪(100 μmol/L)灌流10 min，冲洗10 min，余步骤同对照组。分别用玻璃微电极技术记录心室乳头肌细胞电生理特性的改变。结果: ⑴ 再灌注5 min、10 min实验组和预先给药组APD50、APD90均明显短于对照组(P<0.01，P<0.05)，而再灌注30 min又明显长于对照组(P<0.01，P<0.05)。⑵ 实验组和预先给药组再灌注30 min动作电位振幅(APA)、超射值(OS)、0期最大除极速度(Vmax) 恢复早于对照组，且复跳时间明显短于对照组(P<0.05)。⑶ 3组停搏后静息电位没有明显差异，预给药组停搏时间长于对照组(P<0.05)。结论: 含二氮嗪的St．Thomas停搏液对缺血再灌注豚鼠心室乳头肌细胞电生理特性的保护效果强于单纯的二氮嗪预先给药和传统的St．Thomas停搏液。     

Effects of hypoxia on passive electrical properties of canine ventricular muscle

The effect of hypoxia, either in the presence or in the absence of glucose, on the passive electrical properties of canine ventricular muscle fibers was examined, employing a single sucrose gap method. The significant changes after 30 min of hypoxia (PO ₂=35–45mm Hg) were an increase in the specific internal longitudinal resistance (R _i) and a decrease in the space constant (). The values during the control (PO ₂>450mm Hg) were 198±77 cm forR _i and 0.81±0.15 mm for , and they changed to 245±90 cm and 0.70±0.10mm, respectively, after 30min of hypoxia. Hypoxia decreased the specific membrane resistance (R _m), but the changes were not statistically significant. The membrane time constant ( _m ) and capacity (C{imm}) were not affected significantly. The absence of glucose during hypoxia was found to cause more profound changes than hypoxia alone in the passive electrical properties, especiallyR _i and , suggesting that glucose might counteract the effects of hypoxia on these parameters of ventricular muscles.     

聚乙二醇化重组人生长激素对离体豚鼠乳头肌细胞动作电位的影响

目的 探讨聚乙二醇化重组人生长激素(PEG-rhGH)对离体豚鼠乳头肌细胞动作电位的影响,并以重组人生长激素(rhGH)为阳性对照物比较二者的体外生物活性.方法 健康雄性DHP豚鼠12只,随机分为2组,PEG-rhGH干预组和rhGH干预组,每组6只.采用累计给药法和给药前后自身对照方法,分别观察不同质量浓度(1、5、...     

The stiffness of parallel elastic elements in rat papillary muscle

Summary The dynamic stress-strain relationship of the parallel elastic element (PE) in rat papillary muscle has been investigated.This relationship cannot be correctly estimated by means of the classical diagram: muscle length-stable passive tension of the whole muscle. A new experimental approach has been developed by which the elastic properties of PE may be measured under dynamic conditions.After isometric stabilization of the muscle at a series of preloads, tension changes following quick release were measured. The tension-length relationships measured under these conditions were used to evaluate the elastic behaviour of the parallel elements.The results obtained show that the stiffness of PE is higher than expected and that its maximum elongation never exceeds 10% of the respectiveL _o value at all preload levels explored.Preliminary communication at: International Congress of Physiological Sciences, Munich, July 1971. This study was partially supported by a grant from the Consiglio Nazionale delle Ricerche (CNR, Rome, Italy).     

豚鼠心室肌细胞急性分离法中的要则

目的：探讨酶解分离豚鼠心室肌细胞过程中容易忽视的因素及应予重视的要求。方法：采用Langendorff灌流，先用无钙液灌流4-5 min，再用含胶原酶I 0.1 g/L、蛋白酶E 0.01 g/L、BSA 0.5 g/L的无钙液灌流8-10 min，接着用KB液冲洗4-5 min后剪下心室肌，剪碎，过滤，静置后复钙进行膜片钳实验。结果：通过仔细调整和控制细胞分离过程中的各种问题和影响因素，得到结构完整、长杆状、耐钙的心室肌细胞。结论：积极探索和总结细胞分离过程中的关键问题，可顺利得到适于膜片钳记录的单个心室肌细胞。     

Voltage-dependent properties of macroscopic and elementary calcium channel currents in guinea pig ventricular myocytes

Whole-cell Ca channel currents were recorded from guinea pig ventricular myocytes that were internally perfused with Cs solution and bathed in solutions containing 3.6 mM Ca, 3.6 mM Ba or 90 mM Ba (34° C). Single Ca channel currents were recorded from cell-attached membrane patches of similar myocytes; the patch pipettes contained a 90 mM Ba solution. 1. Although the shape of the whole-cellI–V relation was independent of the bathing solution, this was not the case with the location of the inward current maximum (V _peak);V _peak in 90 mM Ba was about 30 mV positive toV _peak in 3.6 mM Ba. 2. The activation and inactivation of whole-cell currents were voltage dependent. Compared to the voltage dependencies in 3.6 mM Ba, those in 90 mM Ba were shifted by about 30 mV to the right, suggesting a neutralization of surface charges. 3. Observations compatible with the ion permeation model proposed by Hess and Tsien (1984) included (a) a depression of current during Ca/Ba solution exchange, (b) a high divalent to monovalent ion permeability, and (c) rectification of the outward limb of theI–V relation. 4. Estimated current densities atV _peak were similar for myocytes in 3.6 mM Ca and 3.6 mM Ba, and about 10 times larger in 90 mM Ba. 5. Average currents (I ^*) calculated from ensembles of records of single Ca channel current had voltage-dependent time courses resembling those of whole-cellI _Ba (90 mM). 6. Single-channelI ^*–V relations were superimposable on whole-cellI–V curves suggesting that voltage-dependent single-channel parameters (probability of opening, elementary current amplitude) can be related to the voltage-dependent macroscopic current parameters (activation, instantaneousI–V relation) when scaled by channel number. 7. The density of Ca channels in myocytes was calculated from whole-cellI _Ba (90 mM) and average current through single channels. The outcome, 3–5 channels/m², agrees with two other recent estimates (Tsien et al. 1983; Lux and Brown 1984). However, it is difficult to reconcile with the much lower density that one would forecast from the frequency of functional channel observation in myocyte membrane patches (Pelzer et al. 1985c).Supported by the Deutsche Forschungsgemeinschaft (DFG), SFB 38 (Membranforschung), project G1, and the Medical Research Council (Canada)     

Ammonium chloride-induced modification of the effect of sodium nitroprusside on the contractility of guinea pig papillary muscle

Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 116, N ^o 10, pp. 440–442, October, 1993     

Magnesium restores high K-induced inactivation of the fast Na channel in guinea pig ventricular muscle

The effect of extracellular magnesium concentration (Mg_o) on the upstroke of the action potential was studied in guinea pig ventricular muscle under various K⁺ concentrations (2.7–19mM). Increased Mg_o shifted the steady state inactivation curve of the fast Na channel in the depolarizing direction and this effect was concentration-dependent (0–20mM). Such an effect could explain the Mg-induced increase in maximum rate of rise of the action potential which Späh and Fleckenstein (1979) proposed to be due to a Mg channel.     

Effect of collagen digestion on the passive elastic properties of diaphragm muscle in rat

Effects of collagen digestion have been defined up to the fibril level. However, the question remains as to whether the alteration of skeletal muscle extracellular matrix (ECM) affects a muscle's passive elastic response. Various elastography methods have been applied as tools for evaluating the mechanical properties and ECM content of skeletal muscle. In an effort to develop an ECM altered skeletal muscle model, this study determined the effect of collagen digestion on the passive elastic properties of skeletal muscle. Passive mechanical properties of rat diaphragms were evaluated in various degrees of collagen digestion. Between cyclic loading tests, muscle strips were immersed in various concentrations of clostridium histolyticum derived bacterial collagenase. All samples were later viewed via light microscopy. Cyclic testing revealed linear relationships between passive muscle stiffness and digestion time at multiple concentrations. These results demonstrate that collagenase digestion of the ECM in skeletal muscle could be used as a simple and reliable model of mechanically altered in vitro tissue samples.     

Isolation and contractile properties of single smooth muscle cells from guinea pig taenia caeci

A method for the isolation of single smooth muscle cells from guinea pig taenia caeci is described. The single cells were prepared by digestion with 0.3% collagenase and 0.6% trypsin inhibitor in Ca2+-free solution. This procedure produced a high yield of intact cells. Most cells obtained by this procedure were relaxed and showed large contractile responses to excitatory stimulus. Maximal responses of the single cells to acetylcholine (ACh), histamine, and high K+ were attained within 20 sec, and the per cent decrease in cell length was 30-40%. Times for maximal responses of the single cells were shorter than those of the muscle strips. Single cells exhibited a dose-dependent graded response to calcium under depolarized conditions, ACh, histamine, and high K+, and a voltage- and duration-dependent response to electrical stimulation. The ED50s of ACh in the single cells and in the muscle strips were about 2 X 10(-8) and 1.5 X 10(-7) M, respectively. The muscle strips had a lower sensitivity than the single cells to ACh. The generally smooth surface of the relaxed cell contrasted with the numerous evaginations present on the fully contracted cell. I believe that single smooth muscle cells isolated from guinea pig using my technique are, at present, better for physiological and pharmacological studies than are cells isolated using other techniques.     

Quantitative analysis of tenascin in chordae tendineae of human left ventricular papillary muscle with aging.

A computer image analysis was done to investigate the distribution of tenascin and collagenous matrix components (collagen types I and III) in the chordae tendineae of the anterior cusp of the left ventricular papillary muscle, using confocal laser scanning microscopy in both a 20s age group and an 80s-90s age group. Tenascin and the collagenous matrix components showed marked accumulation in the 80s-90s age group with elastic fiber concentration being increased in the same region as that in the 20s age group. The highest content of intersurface layer staining with an anti-tenascin antibody and with anti-collagen type III in the inner layer was found in the 80s-90s age group. These content levels were low in each region in the 20s age group. The distribution and content of these extracellular matrix changes are related to the changes in mechanical performance of the cardiac muscle with age.     

Action of ionophore A23187 on the strength of contraction and transmembrane action potential of guinea pig papillary muscle

The calcium ionophore A23187, in a concentration of 2.5 M, caused a two- to threefold increase in the strength of the contraction of the isolated papillary muscle of the guinea pig heart, stimulated at a frequency of 0.2 Hz. The ionophore A23187 reduced the resting voltage of the preparation in the intertrial interval and reduced the total duration of contraction. The increase in the strength of contraction was not accompanied by any change in the amplitude or duration of the transmembrane action potential. In the presence of the ionophore the ascending phase of a single contraction cycle showed a discontinuity separating the development of the twitch into two phases; differentiation of the twitch gave two positive maxima. The substance D-600, which blocks the calcium current, reduced the duration of the action potential and inhibited the second phase of twitch development, but caused no change in the magnitude or rate of the first phase of contraction. It is suggested that under the influence of the ionophore the component of the twitch which is not blocked by D-600 is caused by liberation of calcium from the sarcoplasmic reticulum.Laboratory of Electrophysiology of the Heart and Laboratory of Myocardial Metabolism, All-Union Cardiologic Scientific Center, Academy of Medical Sciences of the USSR, Moscow. Department of Pharmacology, Vanderbilt University, Nashville, USA. (Presented by Academician of the Academy of Medical Sciences of the USSR V. V. Zakusov.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 85, No. 6, pp. 690–693, June, 1978.