Evaluation of the osmoregulatory function of taurine in brain cells

Summary Homogenous primary cultures of mouse astrocytes and cortical neurons were used to clarify the role of taurine in ion and osmoregulation in the CNS. This study indicates that both neurons and glial cells have uptake systems for taurine. The cell water content does not change during loading of cells with taurine. Chemical analysis indicates that part of the accumulated taurine is metabolized and that the product(s) are stored in the cells. Extracellular taurine (1 mM) has no effect on K⁺, Na⁺, Cl^-, or Ca²⁺ movements in astrocytes. However, astrocytes loaded to a taurine content which corresponds a concentration of 60 mM (corresponds to normal mouse cortex levels) show a 50% reduction in their K⁺ accumulation by carriers and a 100% increase in Ca²⁺ turnover rates. Movements of Ca²⁺ and K⁺ are involved in neurotransmission. It appears that taurine stored in glial cells, has an important effect on ion homeostasis in the CNS and may act indirectly on neuronal excitability.     

Lysophosphatidic acid induces human natural killer cell chemotaxis and intracellular calcium mobilization

We have investigated the effects of the bioactive lipid lysophosphatidic acid (LPA) on several functions of activated human natural killer (NK) cells. Flow cytometric and immunoblot analyses show that these cells express LPA(1, )LPA(2) and LPA(3). LPA but not its precursor phosphatidic acid (PA) induces the chemotaxis of NK cells, an activity that is inhibited by prior treatment of the cells with pertussis toxin (PTX). In addition, LPA induces the mobilization of intracellular calcium, an effect that is markedly inhibited by PTX, but is not inhibited by the addition of EGTA. PA also induces calcium flux in NK cells, but with much lower efficacy than LPA. Cross-desensitization experiments demonstrate that LPA and PA utilize different receptors. Moreover, LPA or PA but not sphingosine 1-phosphate, enhances IFN-gamma secretion by activated NK cells. Our results may shed some light on the findings that activated NK cells are found at the sites of tumor growth.     

Mobilization of free Ca2+ measured during contraction-relaxation cycles in smooth muscle cells of the porcine coronary artery using quin2

Ca²⁺ mobilization in dispersed smooth muscle cells of the porcine coronary artery was investigated using the fluorescent Ca²⁺ indicator, quin2. The resting [Ca²⁺]_i was 113±8 nM (a mean±SE), and was independent of intracellular quin2 concentrations. Acetylcholine (ACh; over 10 nM) or caffeine (over 3 mM) transiently increased the intensity of fluorescence, thereby reflecting the elevation of intracellular free Ca²⁺ (Ca²⁺ transient), while excess K⁺ gradually increased and maintained the intensity of fluorescence. Application of EGTA reduced the resting intensity of the fluorescence and blocked the K⁺-induced Ca²⁺ transient, but did not supress the Ach-or caffeine-induced ones. Nisoldipine (0.1 M) did not affect the resting intensity of the fluorescence. This agent blocked the K⁺ induced but not the ACh-or caffeine-induced Ca²⁺ transient. Thus, sources of Ca²⁺ contributing to the K⁺-induced Ca²⁺ transient differ from those evoked by other agents. The amount of Ca²⁺, as estimated from the increased Ca²⁺ transient by caffeine or ACh, was increased in proportion to the excess K⁺-induced influx of Ca²⁺.     

Mechanical characteristics of skinned and intact muscle fibres from the giant barnacle,Balanus nubilus

Intact muscle fibres fromBalanus nubilus develop tensions of up to 600 kN sd m⁻² during electrical stimulation. The rise of tension occurs with a half-time (177 ms at 12° C) about fivefold longer than that of tetanised frog muscle at the same temperature. The response of myofibrillar bundles to a rapid stretch resembles that of frog muscle but has a y_o value (i.e. the size of an instantaneous release necessary to just discharge tension) which is ca. 2.5 times smaller, and phase 2 of the tension transient (the “quick phase”) occurs at a rate comparable to that of frog muscle. In contrast, the ATPase activity (0.018 mmoles · kg wet weight⁻¹ · s⁻¹) of this preparation and its maximum shortening velocity (0.15–0.16 muscle lengths · s⁻¹) are both at least fivefold slower than frog muscle. These findings can be accounted for by a cross-bridge cycle in barnacle muscle in which events prior and subsequent to the tension generating step(s) occur at a rate at least fivefold slower than comparable steps in frog muscle, but the step(s) associated with tension development occur at similar rates in the two preparations. Since the rate of mechanical relaxation in barnacle muscle is modified in the presence of intracellular calcium buffers and by depolarisation-induced elevation of the free calcium during the relaxation phase, it is proposed that the time course of relaxation is not determined exclusively by the kinetics of the cross-bridge cycle, but is also dependent on the free calcium concentration during relaxation.     

慢性肾衰大鼠单个核细胞内游离钙浓度和白介素－1活性的变化

本文探讨了５／６肾切除术后慢性肾衰大鼠残肾纤维化的发生机理，发现术后１２０天，在残肾单个核炎性细胞浸润、残肾显著纤维化和肾功能损害的同时，残肾脂质过氧化物含量显著升高，抗氧化机制功能显著下降，钠钾ＡＴＰ酶活力显著下降，周围血单个核细胞内游离钙浓度显著升高，单个核细胞培养上清白介素－１活性增高。而摄入大量维生素Ｅ的大鼠，上述各指标有不同程度的改善，残肾纤维化显著减轻。提示残肾纤维化可能与单个核白细胞内游离钙浓度升高，进而产生白介素－１增多有关。     

Ryanodine: its possible mechanism of action in the caffeine-sensitive calcium store of smooth muscle

The caffeine-sensitive intracellular Ca store was characterized and the mechanism of action of ryanodine in the store was studied using K-depolarized guinea-pig taenia caecum. (1) After incubation of the preparation with CaCl₂ (Ca loading), caffeine was applied in Ca-deprived medium, to produce a transient contraction and to monitor the amount of the stored Ca. As duration of Ca deprivation was prolonged, the amplitude of the caffeine-induced contraction was decreased. When ryanodine was applied during Ca deprivation, the rate of the decrease was remarkably accelerated. (2) The rate of rise of the contraction induced by external Ca ((Ca)o) was slowed by preceding depletion of the stored Ca by caffeine, compared with that observed in the Ca loaded preparation. However, in the presence of ryanodine, even if stored Ca was depleted by caffeine, the rate of rise of the (Ca)o-induced contraction remained at a higher level. (3) These results suggest that ryanodine stimulates a leak of the stored Ca, and that the contraction induced by the transmembrane influxed Ca could be modulated by the amount of Ca in, or leakiness of, the caffeine-sensitive Ca store.     

A low-voltage activated,transient calcium current is responsible for the time-dependent depolarizing inward rectification of rat neocortical neurons in vitro

Intracellular recordings were obtained from rat neocortical neurons in vitro. The current-voltage-relationship of the neuronal membrane was investigated using current- and single-electrode-voltage-clamp techniques. Within the potential range up to 25 mV positive to the resting membrane potential (RMP: –75 to –80 mV) the steady state slope resistance increased with depolarization (i.e. steady state inward rectification in depolarizing direction). Replacement of extracellular NaCl with an equimolar amount of choline chloride resulted in the conversion of the steady state inward rectification to an outward rectification, suggesting the presence of a voltage-dependent, persistent sodium current which generated the steady state inward rectification of these neurons. Intracellularly injected outward current pulses with just subthreshold intensities elicited a transient depolarizing potential which invariably triggered the first action potential upon an increase in current strength. Single-electrode-voltage-clamp measurements reveled that this depolarizing potential was produced by a transient calcium current activated at membrane potentials 15–20 mV positive to the RMP and that this current was responsible for the time-dependent increase in the magnitude of the inward rectification in depolarizing direction in rat neocortical neurons. It may be that, together with the persistent sodium current, this calcium current regulates the excitability of these neurons via the adjustment of the action potential threshold.     

Calcium pump expression in human bone and soft tissue tumours

Ninety-one cases of human bone and soft tissue tumours were studied for calcium pump expression by strepto-avidin-biotin immunohistochemical staining with a monoclonal antibody against sarcoplasmic reticulum calcium-ATPase (mAb6F5). Two out of 5 cases of embryonal rhabdomyosarcoma, 1 out of 5 cases of biphasic synovial sarcoma, 4 of 4 cases of chordoma and all of 3 chondrosarcoma cases were positive for mAb6F5. Although this novel monoclonal antibody can be used as a marker of myogenic tumours, the present positive result for endoplasmic reticulum calcium-ATPase (calcium pump) in other tumours including chordoma, chondrosarcoma and synovial sarcoma indicates a wider immunoreactivity. The findings further suggest that intracellular calcium may play an important role in cell proliferation and/or differentiation.     

肾上腺髓质素对豚鼠心室肌细胞L-型钙通道的作用及其信号转导机制

目的: 研究肾上腺髓质素( adrenomedullin, ADM)抑制豚鼠心室肌细胞L-型钙通道的信号转导机制。方法: 应用全细胞膜片钳技术,记录应用ADM(1-100 nmol·L^-1)前后L-型钙电流(I_Ca,L),以及分别记录应用ADM特异性受体拮抗剂ADM_22-52(100 nmol·L^-1)+ADM(100 nmol·L^-1)、蛋白激酶A (PKA) 特异性拮抗剂H-89(10 μmol·L^-1) + ADM(100 nmol·L^-1)、蛋白激酶C (PKC) 特异性拮抗剂PKC_19-36(10 μmol·L^-1)+ADM(100 nmol·L^-1)、PKC特异性激动剂PMA(1 μmol·L^-1)前后I_Ca,L。结果: ADM(1-100 nmol·L^-1)浓度依赖性地抑制豚鼠心室肌细胞I_Ca,L,并可被ADM_22-52(100 nmol·L^-1)完全阻断;H-89(10 μmol·L^-1)对ADM抑制I_Ca,L的作用无影响。PKC_19-36(10 μmol·L^-1)可完全阻断ADM 对I_Ca,L的抑制效应,且PMA(1 μmol·L^-1)可模拟ADM 对I_Ca,L的抑制效应。结论: ADM作用于特异性ADM受体可浓度依赖性地抑制豚鼠心室肌细胞I_Ca,L,此作用有可能与PKC激活相关。     

Photoelectric recording of mechanical responses of cardiac myocytes

A method to monitor contraction of isolated myocytes by transmicroscopic photometry is illustrated. Two photodiodes are mounted inside an inverse microscope used for visual control of a cell. Illumination of one diode varies in proportion to changes in cell length. The contraction signal is amplified in a comparator circuit. Spatial resolution of the device is in the order of 1 m which corresponds to about 5% of cell shortening in the fully activated state of contraction. The method was tested on isolated myocytes from guinea-pig ventricle. Optical records of contraction in response to action potentials or during voltage clamp compare well with the contractile behaviour of multicellular preparations.