IL-12重组质粒联合骨髓间充质干细胞对MCF-7人乳腺癌细胞侵袭及裸鼠移植瘤生长的影响分析

目的探讨IL-12重组质粒联合骨髓间充质干细胞（BMSC）对MCF-7人乳腺癌细胞侵袭及裸鼠移植瘤生长的影响。 方法分离纯化培养BMSC原代细胞,制备BMSC条件培养基,分析BMSC条件培养基对MCF-7细胞株体外增殖和凋亡的影响;建立裸鼠MCF-7转移瘤模型,分为对照组、BMSC组、IL-12组以及联合组,各组每3 d进行一次瘤内注射,共注射3次,15 d后处死裸鼠,比较各组裸鼠肿瘤、脾脏重量。采用χ²检验、t检验以及方差分析进行统计学分析。 结果BMSC条件培养基能够抑制MCF-7细胞增殖,且随着作用时间的延长其抑制作用升高[24 h（13.42±1.93）%,48 h（16.83±1.77）%,72 h（20.21±2.01）,F = 6.271,P = 0.000]。BMSC条件培养基处理MCF-7细胞,可有效促进MCF-7细胞凋亡,且随着作用时间的延长细胞凋亡率升高[24 h（10.82±2.18）%,48 h（18.73±2.95）%,72 h（28.15±3.52）%,F = 9.215,P = 0.000]。与对照组裸鼠肿瘤体积[1 d（124.12±9.28）mm³,3 d（582.41±17.28） mm³,7 d（983.42±42.10） mm³,15 d（793.46±109.38） mm³]比较,BMSC组[1 d（132.61±12.41） mm³,3 d（378.46±23.08） mm³,7 d（542.61±58.49）mm³,15 d（329.48±47.51） mm³]、IL-12组[1 d（119.85±13.10） mm³,3 d（322.75±26.49） mm³,7 d（518.37±67.54）mm³,15 d（302.17±68.53） mm³]以及联合组[1 d（123.41±8.94）mm³,3 d（217.85±24.03）mm³,7 d（318.29±47.32） mm³,15 d（189.27±37.58）mm³]裸鼠肿瘤体积生长速度均减慢,差异具有统计学意义（F_1d=0.827,F_3d=37.583、F_7d=31.472、F_15d=15.372,P < 0.001）;处死各组裸鼠后裸鼠肿瘤质量比较,BMSC组[（529.42±98.74） mg]、IL-12组[（544.01±117.85）mg]以及联合组[（327.55±78.56） mg]均低于对照组[（877.42±120.11）mg],且联合组裸鼠肿瘤质量最低,差异具有统计学意义（F = 10.821,P < 0.001）;而裸鼠脾指数BMSC组（7.58±1.21）、IL-12组（7.63±1.09）以及联合组（10.03±1.52）均高于对照组（5.37±0.89）,联合组裸鼠脾质量最高,差异具有统计学意义（F = 13.411,P < 0.001）。 结论BMSC在体内外均具有抑制MCF-7肿瘤增殖作用,联合使用pcDNA6/IL-12对裸鼠MCF-7转移瘤抑制具有着明显的协同作用。     

Novel ion channels in the protists, Mougeotia and Saprolegnia, using sub-gigaseals.

Protoplasts of the filamentous alga, Mougeotia, and the filamentous fungal oomycete, Saprolegnia ferax, exhibit two K⁺ ion channels (2–6 pA) using the patch-clamp technique when the seals are less than 1 GΩ (about 100 MΩ). The membrane potential of the protoplasts was near 0 mV as measured intracellularly with double-barreled micropipettes; thus, inward K⁺ flux is due solely to concentration differences. Although conductances are in the range expected for K⁺ channels, the activity at 0 mV is not seen in other organisms under gigaseal conditions. This paper draws attention to the usefulness of this subsidiary patch-clamp technique and the novel characteristics of ion channels in Mougeotia and Saprolegnia.     

The development and validation of a charge-coupled device laser reflectance system to measure the complex cross-sectional shape and area of soft tissues

Determination of the stresses in soft tissues such as ligaments and tendons under uniaxial tension require accurate measurement of their cross-sectional area. Of the many methods available, there are concerns regarding contact methods which exert external loads and deform the cross-sectional shape of soft tissues. Hence, the area measurements are affected. On the other hand, non-contact methods have difficulties in dealing with complex shapes, especially with concavities. To address these problems, a new measurement system using a charge-coupled device (CCD) laser displacement sensor has been developed and tested. This system measures the complete surface profile of the object by rotating the laser 360° around the soft tissue. Then, the cross-sectional shape is reconstructed and the cross-sectional area determined via Simpson's rule. The system's accuracy was first verified with objects of various cross-sectional shapes and areas (cylinder: 23.1, 76.5, 510.3 mm²; cuboid: 34.3, 163.8, 316.7 mm², and cylinder with concavities: 121.4 mm²). The CCD laser reflectance system's accuracy was within 2.0% for these objects. To test biological application, the goat Achilles tendon and the anteromedial bundle of the porcine anterior cruciate ligament specimens were measured and compared to values obtained using another accepted technique, the laser micrometer system. The areas obtained using the CCD laser reflectance system were 4.4% and 9.7% lower than those obtained with the laser micrometer system respectively. These differences could be mainly attributed to concavities. Thus, the CCD laser reflectance system is an improved method for measuring the cross-sectional shape and area of soft tissues since it can detect and account for concavities without physically contacting the specimen.     

Modification of a Scanning Transmission Electron Microscope Specimen Holder for Large Section Viewing

A modification of a scanning transmission electron microscope specimen holder which permits full viewing of large plastic embedded tissue sections is discussed. The method for producing one-centimeter diameter “giant” grids is explained and the procedure for sample preparation is outlined The modification aids the microscopist in his evaluation of tissue structural relationship by providing large areas of tissue for examination and reduces significantly the time required to prepare and examine standard 1-2 mm² electron microscopy tissue sections. Light and electron microscopic evaluations can be made on the same tissue sections.     

Changes of microcirculation in healthy volunteers and patients with septic shock in Xining

Objective: The purpose of this study is to investigate the characteristic of microcirculation in healthy volunteers and patients with septic shock in both Xining(2 260 m) and Nanjing(10 m). Methods: A total of 62 cases, 33 healthy volunteers, 22 cases in Xining,(2 260 m above sea level) and 11 cases in Nanjing(10 m above sea level); and 29 septic shock, 13 cases in Xining and 16 cases in Nanjing were collected. The total vessel density(TVD), perfused vessel density(PVD), proportion of perfused vessel(PPV) and microcirculation flow index(MFI) of both healthy volunteers and septic shock had been investigated by using sidestream dark field(SDF). Analyzed and managed the image data by using AVA3.0 software. Results: In the healthy volunteers in Xining area(22 cases),the volume of TVD(15.59 ± 2.58 mm/mm~2), PVD(15.58 ± 2.58 mm/mm~2) and PPV(96.60% ± 4.63%) were significant higher than the volume of TVD(10.0 ± 2.10 mm/mm~2), PVD(10.81 ± 2.38 mm/mm~2) and PPV(84.24% ± 8.00%) of the volunteers(11 cases) in Nanjing(11 cases). But the MFI(2.17 ± 0.31) of the healthy volunteers in the Xining was significant lower(P0.05) than the MFI(3.21 ± 0.34) in the healthy volunteers of Nanjing. In the septic shock group(13 cases) in the Xining, the volume of TVD(5.44 ± 1.94 mm/mm~2), PVD(4.18 ± 1.61 mm/mm~2), PPV(42.14%± 5.38%) and MFI(1.05 ± 0.32) compared with the volume of the healthy volunteers in Xining, the TVD(15.59 ± 2.58 mm/mm~2), PVD(5.58 ± 2.58 mm/mm~2), PPV(96.60% ± 4.63%) and MFI(2.17 ± 0.30) were significant lower(P0.05). In the healthy volunteers compare with septic shock group in Nanjing area, the TVD(6.80±1.72 vs 10.00±2.10, P0.05), PVD(5.86±1.58 vs10.81±2.38,P0.05), PPV(45.42±4.86 vs 84.24±4.86, P0.05), MFI(1.28±0.28 vs 3.21±0.34 P0.05), there was significant decreased. In the septic shock group in the Xining compared with the septic shock in Nanjing, there was no significant difference. 10 of 13 patients with septic shock were survived in Xining. 13 of 16 patients with septic shock were survived in Nanjing. Conclusion: The changes of physiological and pathophysiological characteristic in microcirculation induced by hypoxia would be useful for clinical treatment of septic shock at high altitude.     

Meniscofemoral ligaments--structural and material properties

The meniscofemoral ligaments (MFLs) of 28 human cadaveric knees were studied to determine their incidence, structural and material properties. Using the Race–Amis casting method for measurement, the mean cross-sectional area for the anterior MFL (aMFL) was 14.7 mm² (±14.8 mm²) whilst that of the posterior MFL (pMFL) was 20.9 mm² (±11.6 mm²). The ligaments were isolated and tensile tested in a materials testing machine. The mean loads to failure were 300.5 N (±155.0 N) for the aMFL and 302.5 N (±157.9 N) for the pMFL, with elastic moduli of 281 (±239 MPa) and 227 MPa (±128 MPa), respectively. These significant anatomical and material properties suggest a function for the MFL in the biomechanics of the knee, and should be borne in mind when considering hypotheses on MFL function. Such hypotheses include roles for the ligaments in knee stability and guiding meniscal motion.     

Dopamine D2-Receptor Isoforms Expressed in AtT20 Cells Inhibit Q-Type High-Voltage-Activated Ca2+ Channels via a Membrane-Delimited Pathway

Abstract : Dopamine D₂ receptors both acutely and chronically inhibit high-voltage-activated Ca²⁺ channels (HVA-CCs). Two alternatively spliced isoforms, D_2L (long) and D_2S (short), are expressed at high levels in rat pituitary intermediate lobe melanotropes but are lacking in anterior lobe corticotropes. We stably transfected D_2L and D_2S into corticotrope-derived AtT20 cells. Both isoforms coupled to inhibition of Q-type calcium channels through pertussis toxin-sensitive G proteins. Thus, we have created a model system in which to study the kinetics of D₂-receptor regulation of Ca²⁺ channels. Rapid inhibition of HVA-CCs was characterized using a novel fluorescence video imaging technique for the measurement of millisecond kinetic events. We measured the time elapsed (lag time) between the arrival of depolarizing isotonic 66 m M K⁺, sensed by fluorescence from included carboxy-X-rhodamine (CXR), and the beginning of increased intracellular Ca²⁺ levels (sensed by changes in indo 1 fluorescence ratio). The lag time averaged 350-550 ms, with no significant differences among cell types. Addition of the D₂-agonist quinpirole (250 μ M ) to the K⁺/CXR solution significantly increased the lag times for D₂-expressing cells but did not alter the lag time for AtT20 controls. The increased lag times for D_2L - and D_2S-transfected cells suggest that at least a fraction of the Ca²⁺ channels was inhibited within the initial 350-550 ms. As this inhibition time is too fast for a multistep second messenger pathway, we conclude that inhibition occurs via a membrane-delimited diffusion mechanism.     

Ca2+-Dependent Inactivation of P-Type Calcium Channels in Nerve Terminals

Abstract: Rapid Ca²⁺ signals evoked by K⁺ depolarization of rat cerebral cortical synaptosomes were measured by dual-channel Ca²⁺ spectrofluorometry coupled to a stopped-flow device. Kinetic analysis of the signal rise phase at various extracellular Ca²⁺ concentrations revealed that the responsible voltage-dependent Ca²⁺ channels, previously identified as P-type Ca²⁺ channels, inactivate owing to the rise in intracellular Ca²⁺ levels. At millimolar extracellular Ca²⁺ concentrations the channels were inactivated very rapidly and the rate was dependent on the high influx rate of Ca²⁺, thus limiting the Ca²⁺ signal amplitudes to 500–600 n M. A slower, probably voltage-dependent regulation appears to be effective at lower Ca²⁺ influx rates, leading to submaximal Ca²⁺ signal amplitudes. The functional feedback regulation of calcium channels via a sensor for intracellular Ca²⁺ levels appears to be responsible for the different inhibition characteristics of Cd²⁺ versus ω-agatoxin IVa.     

A Toxin Fraction (FTX) from the Funnel-Web Spider Poison Inhibits Dihydropyridine-Insensitive Ca2+ Channels Coupled to Catecholamine Release in Bovine Adrenal Chromaffin Cells

Abstract: In adrenal chromaffin cells, depolarization-evoked Ca²⁺ influx and catecholamine release are partially blocked by blockers of L-type voltage-sensitive Ca²⁺ channels. We have now evaluated the sensitivity of the dihydropyridine-resistant components of Ca²⁺ influx and catecholamine release to a toxin fraction (FTX) from the funnel-web spider poison, which is known to block P-type channels in mammalian neurons. FTX (1:4,000 dilution, with respect to the original fraction) inhibited K⁺-depolarization-induced Ca²⁺ influx by 50%, as monitored with fura-2, whereas nitrendipine (0.1–1 μ M ) and FTX (3:3), a synthetic FTX analogue (1 m M ), blocked the [Ca²⁺]_i transients by 35 and 30%, respectively. When tested together, FTX and nitrendipine reduced the [Ca²⁺]_i transients by 70%. FTX or nitrendipine reduced adrenaline and noradrenaline release by ∼80 and 70%, respectively, but both substances together abolished the K⁺-evoked catecholamine release, as measured by HPLC. The ω-conotoxin GVIA (0.5 μ M ) was without effect on K⁺-stimulated ⁴⁵Ca²⁺ uptake. Our results indicate that FTX blocks dihydropyridine- and ω-conotoxin-insensitive Ca²⁺ channels that, together with L-type voltage-sensitive Ca²⁺ channels, are coupled to catecholamine release.     

Local Ca2 Rise Near Store Operated Ca2 Channels Inhibits Cell Coupling During Capacitative Ca2 Influx

Using a new fluorescence imaging technique, LAMP, we recently reported that Ca²⁺ influx through store operated Ca²⁺ channels (SOCs) strongly inhibits cell coupling in primary human fibroblasts (HF) expressing Cx43. To understand the mechanism of inhibition, we studied the involvement of cytosolic pH (pH_i) and Ca²⁺([Ca²⁺]_i) in the process by using fluorescence imaging and ion clamping techniques. During the capacitative Ca²⁺ influx, there was a modest decline of pH_i measured by BCECF. Decreasing pH_i below neutral using thioacetate had little effect by itself on cell coupling, and concomitant pH_i drop with thioacetate and bulk [Ca²⁺_i rise with ionomycin was much less effective in inhibiting cell coupling than Ca²⁺ influx. Moreover, clamping pH_i with a weak acid and a weak base during Ca²⁺ influx largely suppressed bulk pH_i drop, yet the inhibition of cell coupling was not affected. In contrast, buffering [Ca²⁺_i with BAPTA, but not EGTA, efficiently prevented cell uncoupling by Ca²⁺ influx. We concluded that local Ca²⁺ elevation subjacent to the plasma membrane is the primary cause for closing Cx43 channels during capacitative Ca²⁺ influx. To assess how Ca²⁺ influx affects junctional coupling mediated by other types of connexins, we applied the LAMP assay to Hela cells expressing Cx26. Capacitative Ca²⁺ influx also caused a strong reduction of cell coupling, suggesting that the inhibitory effect by Ca²⁺ influx may be a more general phenomenon.     

Potassium ion channels in the plasmalemma

The potassium ion is an indispensible cytosolic component of living cells and a key osmolyte of plant cells, crossing the plasmalemma to drive physiological processes like cell growth and motor cell activity. K⁺ transport across the plasmalemma may be passive through channels, driven by the electrochemical gradient, K⁺ equilibrium potential (E_K) – membrane potential (V_m), or secondary active by coupling through a carrier to the inward driving force of H⁺ or Na⁺. Known K⁺ channels are permeable to monovalent cations, a permeability order being K⁺ > Rb⁺ > NH₄⁺ > Na⁺≥ Li⁺ > Cs⁺. The macroscopic K⁺ currents across a cell or protoplast surface commonly show rectification, i.e. a V^m-dependent conductance which in turn, may be controlled by the cytosolic activity of Ca²⁺, of K⁺, of H⁺, or by the K⁺ driving force. Analysis by the patch clamp technique reveals that plant K⁺ channels are similar to animal channels in their single channel conductance (4 to 100 pS), but different in that a given channel population slowly activates and may not inactivate at all. Single-channel kinetics reveal a broad range of open times (ms to s) and closed times (up to 100 s). Further progress in elucidating plant K⁺ channels will critically depend on molecular cloning, and the availability of channel-specific (phyto)toxins.     

The function of Ca channel subtypes in exocytotic secretion: new perspectives from synaptic and non-synaptic release

By mediating the Ca²⁺ influx that triggers exocytotic fusion, Ca²⁺ channels play a central role in a wide range of secretory processes. Ca²⁺ channels consist of a complex of protein subunits, including an ₁ subunit that constitutes the voltage-dependent Ca²⁺-selective membrane pore, and a group of auxiliary subunits, including β, γ, and ₂–δ subunits, which modulate channel properties such as inactivation and channel targeting. Subtypes of Ca²⁺ channels are constituted by different combinations of ₁ subunits (of which 10 have been identified) and auxiliary subunits, particularly β (of which 4 have been identified). Activity-secretion coupling is determined not only by the biophysical properties of the channels involved, but also by the relationship between channels and the exocytotic apparatus, which may differ between fast and slow types of secretion. Colocalization of Ca²⁺ channels at sites of fast release may depend on biochemical interactions between channels and exocytotic proteins. The aim of this article is to review recent work on Ca²⁺ channel structure and function in exocytotic secretion. We discuss Ca²⁺ channel involvement in selected types of secretion, including central neurotransmission, endocrine and neuroendocrine secretion, and transmission at graded potential synapses. Several different Ca²⁺ channel subtypes are involved in these types of secretion, and their function is likely to involve a variety of relationships with the exocytotic apparatus. Elucidating the relationship between Ca²⁺ channel structure and function is central to our understanding of the fundamental process of exocytotic secretion.     

Electrophysiology of mammalian Schwann cells

Schwann cells are the satellite cell of the peripheral nervous system, and they surround axons and motor nerve terminals. The review summarises evidence for the ion channels expressed by mammalian Schwann cells, their molecular nature and known or speculated functions. In addition, the recent evidence for gap junctions and cytoplasmic diffusion pathways within the myelin and the functional consequences of a lower-resistance myelin sheath are discussed.

The main types of ion channel expressed by Schwann cells are K⁺ channels, Cl⁻ channels, Na⁺ channels and Ca²⁺ channels. Each is represented by a variety of sub-types. The molecular and biophysical characteristics of the cation channels expressed by Schwann cells are closely similar or identical to those of channels expressed in peripheral axons and elsewhere. In addition, Schwann cells express P₂X ligand-gated ion channels. Possible in vivo roles for each ion channel type are discussed. Ion channel expression in culture could have a special function in driving or controlling cell proliferation and recent evidence indicates that some Ca²⁺ channel and Kir channel expression in culture is dependent upon the presence of neurones and local electrical activity.     

Electrophysiological characterization of pathways for K+ uptake into growing and non-growing leaf cells of barley

Potassium is a major osmolyte used by plant cells. The accumulation rates of K⁺ in cells may limit the rate of expansion. In the present study, we investigated the involvement of ion channels in K⁺ uptake using patch clamp technique. Ion currents were quantified in protoplasts of the elongation and emerged blade zone of the developing leaf 3 of barley ( Hordeum vulgare L.). A time-dependent inward-rectifying K⁺-selective current was observed almost exclusively in elongation zone protoplasts. The current showed characteristics typical of Shaker-type channels. Instantaneous inward current was highest in the epidermis of the emerged blade and selective for Na⁺ over K⁺. Selectivity disappeared, and currents decreased or remained the same, depending on tissue, in response to salt treatment. Net accumulation rates of K⁺ in cells calculated from patch clamp current–voltage curves exceeded rates calculated from membrane potential and K⁺ concentrations of cells measured in planta by factor 2.5–2.7 at physiological apoplastic K⁺ concentrations (10–100 m m ). It is concluded that under these conditions, K⁺ accumulation in growing barley leaf cells is not limited by transport properties of cells. Under saline conditions, down-regulation of voltage-independent channels may reduce the capacity for growth-related K⁺ accumulation.     

Coupling of the Cloned μ-Opioid Receptor with the ω-Conotoxin-Sensitive Ca2+ Current in NG108-15 Cells

Abstract: Voltage-dependent Ca²⁺ currents were measured in NG108-15 neuroblastoma × glioma hybrid cells transformed to express the rat μ-opioid receptor by the whole-cell configuration of the patch-clamp technique with Ba²⁺ as charge carrier. A μ-opioid receptor-selective agonist, [ d -Ala², N -Me-Phe⁴,Gly⁵-ol]enkephalin caused significant inhibition of voltage-dependent Ca²⁺ currents in μ-receptor-transformed NG108-15 cells but not in nontransfected or vector-transformed control cells. On the other hand, a δ-opioid receptor-selective agonist, [ d -penicillamine², d -penicillamine⁵]enkephalin, induced inhibition of voltage-dependent Ca²⁺ currents in both control and μ-receptor-transformed cells, which is mediated by the δ-opioid receptor expressed endogenously in NG108-15 cells. The inhibition of voltage-dependent Ca²⁺ currents induced by [ d -Ala², N -Me-Phe⁴,Gly⁵-ol]enkephalin and [ d -penicillamine², d -penicillamine⁵]enkephalin was reduced by pretreatment of the cells with pertussis toxin or ω-conotoxin GVIA. These results indicate that the μ-opioid receptor expressed from cDNA functionally couples with ω-conotoxin-sensitive N-type Ca²⁺ channels through the action of pertussis toxin-sensitive G proteins in NG108-15 cells.     

Electron Microscopy of Mummified Material

It has proved possible to cut ultrathin sections of mummified material obtained from an American Indian burial (approximate age unknown). Small pieces of tissue were placed for 48 hr in a softening fluid consisting of 96% ethyl alcohol, 30 vol.; 1% aqueous formalin, 50 vol.; 5% aqueous Na₂CO₃, 20 vol. During this period the fluid was changed twice. The tissue was then cut with a razor blade into cubes of 1 mm per side or less, dehydrated in graded ethanols, infiltrated and embedded in methacrylate and the plastic polymerised by placing in the oven at 58°C overnight. The blocks were trimmed to a truncated cone leaving a surface area of 0.5 mm² or less, and cut on a Porter Blum ultramicrotome using a glass or a diamond knife.     

Infectivity, growth, development and pathology of Echinostoma caproni (Trematoda) in the golden hamster

Laboratory hamsters (Mesocricetus auratus) were experimentally infected with 75 ± 15 metacercarial cysts of Echinostoma caproni. Worms were recovered from days 7 to 89 post-infection with eight to 90 (average 37) parasites in the small intestine. Worm wet weights averaged 0.85 mg at 10 days, 1.8 mg at 17 days, 3.4 mg at 45 days, and 7.7 mg at 89 days; average dry weights for the identical days were, 0.15, 0.30, 0.70 and 2.2 mg, respectively. The average body area of worms fixed in hot (80°C) alcohol-formalin-acetic acid was 0.21 mm² on day 3, 4.9 mm² on day 10, and 17.7 mm² on day 42. Clinical signs in some hamsters included progressive unthriftiness and watery diarrhea. Gross examination revealed enlarged lymphatic nodules along the length of the small intestine. The histopathological responses of hamsters to the parasite showed erosion of the intestinal villi with lymphocytic infiltration being the primary response; hemorrhagic areas were also observed in the villi.     

Actin Dynamics Regulates Voltage-Dependent Calcium-Permeable Channels of the Vicia faba Guard Cell Plasma Membrane

Free cytosolic Ca²⁺ ([Ca²⁺]_cyt) is an ubiquitous second messenger in plant cell signaling, and [Ca²⁺]_cyt elevation is associated with Ca²⁺-permeable channels in the plasma membrane and endomembranes regulated by a wide range of stimuli. However, knowledge regarding Ca²⁺ channels and their regulation remains limited in planta . A type of voltage-dependent Ca²⁺-permeable channel was identified and characterized for the Vicia faba L. guard cell plasma membrane by using patch-clamp techniques. These channels are permeable to both Ba²⁺ and Ca²⁺, and their activities can be inhibited by micromolar Gd³⁺. The unitary conductance and the reversal potential of the channels depend on the Ca²⁺ or Ba²⁺ gradients across the plasma membrane. The inward whole-cell Ca²⁺ (Ba²⁺) current, as well as the unitary current amplitude and NP_o of the single Ca²⁺ channel, increase along with the membrane hyperpolarization. Pharmacological experiments suggest that actin dynamics may serve as an upstream regulator of this type of calcium channel of the guard cell plasma membrane. Cytochalasin D, an actin polymerization blocker, activated the NPo of these channels at the single channel level and increased the current amplitude at the whole-cell level. But these channel activations and current increments could be restrained by pretreatment with an F-actin stabilizer, phalloidin. The potential physiological significance of this regulatory mechanism is also discussed.     

Hypoosmotic shock activates Ca channels in isolated nerve terminals

Influence of hypotonic swelling on Ca²⁺ (⁴⁵Ca²⁺) uptake in rat brain synaptosomes was studied. A decrease in medium osmolality from 310 to 260-180 mOsm led to a progressive stimulation of ⁴⁵Ca²⁺ accumulation. The effect was blocked by verapamil (IC₅₀ = 5 μM), CoCl₅₀ = 58 μM) and retained at a fixed concentration of external sodium indicating the involvement of Ca²⁺ channels rather than Na⁺/Ca²⁺ exchange in swelling-induced Ca²⁺ influx. The populations of calcium channels observed in hypoosmotic and depolarizing conditions are different in three aspects: (i) kinetics of ⁴⁵Ca²⁺ entry; (ii) insensitivity to dihydropyridines and ω-conotoxin GVIA; (iii) insensitivity to preliminary depolarization by high potassium. The effects of swelling and depolarization on Ca²⁺ uptake were additive. No change in membrane potential monitored with diS-C₃-(5) was recorded during synaptosome hypotonic swelling. The results suggest the existence in synaptosomal plasma membrane of volume-dependent calcium-permeable channels with properties distinct from those of the voltage-dependent calcium channels. Activation of these channels may constitute an early event in volume regulation of nerve terminals in anisoosmotic conditions.     

Depletion of intracellular calcium stores activates an outward potassium current in mast and RBL-1 cells that is correlated with CRAC channel activation

Highly Ca²⁺ selective Ca²⁺ channels activated by store depletion have been recently described in several cell types and have been termed CRAC channels (for calcium release-activated calcium). The present study shows that following store depletion in mast and RBL-1 cells, monovalent outward currents could be recorded if the internal solution contained K⁺ but not Cs⁺. The activation of the outward K⁺ current correlated with the activation of I_CRAC, in both time and amplitude, suggesting that the K⁺ current might be carried by CRAC channels. The amplitude of the outward current was increased if external Ca²⁺ was reduced or replaced by external Ba²⁺. The outward K⁺ conductance might have a physiological role in maintaining the driving force for Ca²⁺ entry during the activation of CRAC channels.