NO对新生大鼠下丘脑钙激活钾通道的直接激活作用

目的：研究NO对下丘脑神经元钙激活钾通道（K_Ca）的作用及其机制。方法：采用膜片钳技术内面向外式。结果：NO可显著提高通道的开放概率，这种增强作用是通过延长通道开放时间及增加开放频率实现的。结论：下丘脑神经元中NO可直接激活K_Ca，它的病理生理作用还有待于进一步研究。     

医用磷酸钙骨水泥的制备及性能的实验研究

探索了磷酸四钙（Ca4（PO4）2O，TTCP）的制备，并合成了磷酸钙骨水泥（CPC），对CPC固化时间、引起浸泡液pH值的变化、抗压强度、产物物相组成及微观结构进行了研究。结果表明：在真空条件下、1500℃下煅烧6h可制得TTCP，并含有少量CaO。CPC初凝时间为4min、终凝时间为15min，浸泡1d和7d后的抗压强度分别为20MPa和35MPa，浸泡液的pH值在6．4～8．9之间变化，这些性能均符合临床用CPC的性能要求。CPC水化产物为片状或针状羟基磷灰石（Ca5（PO4）3OH，HA），相互交错呈连续分布的网状结构，这种结构有利于材料强度的提高。实验研制的CPC材料可用于骨缺损的修复治疗。     

Juvenile sudden death in a family with polymorphic ventricular arrhythmias caused by a novel RyR2 gene mutation: evidence of specific morphological substrates

We report on a family with a history of sudden death and effort-induced polymorphic ventricular arrhythmias. The index case was a 17-year-old boy who died suddenly and at postmortem had evidence of fibrofatty replacement in the right ventricular free wall, consistent with arrhythmogenic right ventricular cardiomyopathy, as well as calcium phosphate deposits within the myocytes. A molecular genetics investigation carried out in the paraffin-embedded myocardium of the subject and in blood samples of family members disclosed a missense mutation in exon 3 (230C-->T; A77V) of the cardiac ryanodine receptor type 2 gene. The carriers showed effort-induced polymorphic ventricular tachycardia in the setting of normal resting electrocardiogram and trivial echocardiographic abnormalities, consistent with catecholaminergic polymorphic ventricular tachycardia. The observation of both arrhythmogenic right ventricular cardiomyopathy type 2 and catecholaminergic polymorphic ventricular tachycardia in the same family suggests that the two entities might correspond to different degrees of phenotypic expression of the same disease. This experience underscores the importance of a precise autopsy diagnosis in the case of sudden cardiac death, including molecular genetics, and the mission of pathologists to guide further clinical investigation of family members.     

Regulation of GABA release by depolarisation-evoked Ca2+ transients at a single hippocampal terminal

We correlated dynamic changes in free cytosolic [Ca²⁺] ([Ca²⁺]_i) within single presynaptic terminals of cultured hippocampal neurones with the postsynaptic GABA-mediated currents. The local changes in [Ca²⁺]_i and evoked inhibitory postsynaptic currents (eIPSCs) were recorded simultaneously using Fura-2 fluorescence and whole-cell patch-clamp respectively. The Ca²⁺ signals and eIPSCs were evoked by direct extracellular electrical stimulation of a single presynaptic terminal by short depolarising pulses. The presynaptic Ca²⁺ transient was graded by varying the amplitude of extracellular stimulating pulses. The probability of the release event, P, estimated for each stimulation strength, reached a maximum (P=1) when the Ca²⁺ signal became maximal and remained at this level at higher stimulation strength, despite the subsequent decrease in the amplitude of the Ca²⁺ transient. A gradual, linear increase in stimulation amplitude (V_stim) resulted in a bell-shaped dependence of the averaged amplitudes of Ca²⁺ signals and corresponding averaged amplitudes of eIPSCs. Analysis of the eIPSC demonstrated that the decrease in both the mean eIPSC amplitude and the mean quantal content of release resulted from a reduction in the probability of multivesicular release, i.e. in the disappearance of failures and in the decrease of individual eIPSC amplitude. The Ca²⁺ signals of similar amplitude resulted in both random and determinate (non-random) neurotransmitter release. We conclude that depolarisation-induced elevation of [Ca²⁺]_i within the terminal is necessary but not sufficient for activation of vesicular release of neurotransmitter.     

毛细胞PMCA2在小鼠内耳Ca2+调节和听觉平衡中的作用

目的： 研究小鼠内耳毛细胞细胞膜Ca²⁺-ATP酶2型蛋白（PMCA2）在听觉平衡生理中的作用及意义。 方法：利用不同基因型小鼠PMCA2^-/-(突变纯合子)、PMCA2^+/-(杂合子)和PMCA2^+/+(野生型)为实验对象，采用听觉脑干反应(ABR)、畸变产物耳声发射(DPOAE)和耳蜗内电位(EP)检测等方法，分别检测不同基因型小鼠的内耳生理功能。结果：PMCA2^+/+野生型鼠的听力正常，ABR的短声(click)阈值为(13.75±11.08)dB SPL；EP均值为(91.3±11.0)mV。PMCA2^+/-杂合子小鼠听力低于同窝PMCA2^+/+野生型鼠，ABR的短声阈值为(63.89±12.90)dB SPL，与PMCA2^+/+小鼠比较差异显著(P<0.01)；PMCA2^+/-小鼠没有检测出DPOAE的高频区辐值，其EP均值为(80.7±9.0)mV。PMCA2^-/-小鼠的ABR在100 dB SPL无反应，表现出全聋和平衡功能失调，其EP均值为(56.6±13.0)mV；PMCA2^-/-小鼠没有检测出DPOAEs。结论：PMCA2是内耳毛细胞纤毛丛上的重要Ca²⁺转运通道，对维持内耳的Ca²⁺代谢和听觉平衡功能有重要作用。     

A rapidly inactivating Ca2+-dependent K+ current in pheochromocytoma cells (PC12) of the rat

The membrane electrical properties of undifferentiated pheochromocytoma cells of the rat (PC12) were studied using both current-and voltage-clamp techniques with the use of low-resistance blunt-tipped micropipettes (patch electrodes). In the presence of tetrodotoxin (TTX, 2–3 M), a spike-like wave form with a prominent after-hyperpolarization (AHP) was recorded following brief (< 10 ms) depolarizing current pulses. The inorganic divalent cations, Cd²⁺ (0.5 mM), Mn²⁺ (4mM), and 0 mM Ca²⁺/4 mM Mg²⁺ solution prolonged the duration, attenuated the AHP, slowed the rate of repolarization, and slightly enhanced the amplitude of this wave form. A rapidly inactivating outward current was recorded in over 70% of the cells under voltage-clamp conditions. This transient current was elicited at about ±30 mV, and was blocked by tetraethylammonium (5 mM), inorganic divalent cations (Cd²⁺, 0.5 mM; Mn²⁺, 4 mM; Ba²⁺, 3 mM), and removal of Ca²⁺ (0 mM Ca²⁺/4 mM Mg²⁺) from the local perfusion medium. In addition, 4-aminopyridine (5 mM), which blocks the transient outward K⁺ current I_A in a variety of excitable cells, did not have any appreciable effect on this rapidly inactivating current. Moreover, it was possible to elicit the current at a holding potential of ±40 mV. The reversal potential of this current was ±90 mV, and shifted positively when extracellular K⁺ concentrations were elevated. It is concluded that PC12 cells have a rapidly inactivating Ca²⁺ -dependent K⁺ current. A possible explanation for the transient nature of this current may be the presence of an effective intracellular Ca²⁺ buffering (uptake or extrusion) system.     

Physiological mechanisms of TRPC activation

TRPC (canonical transient receptor potential) channels are vertebrate homologs of the Drosophila photoreceptor channel, TRP. Considerable research has been brought to bear on the seven members of this family, especially with regard to their possible role in calcium entry. Unfortunately, the current literature presents a confusing picture, with different laboratories producing widely differing results and interpretations. It appears that ectopically expressed TRPC channels can be activated by phospholipase C products (generally, diacylglycerols), by stimulation of trafficking to the plasma membrane, or by depletion of intracellular Ca²⁺ stores. Here, I discuss the possibility that these diverse experimental findings arise because TRPC channels can, under both experimental as well as physiological conditions, be activated in three distinct ways, possibly depending on their subunit composition and/or signaling complex environment. The TRPCs may be unique among ion-channel subunit families in being able to participate in the assembly and function of multiple types of physiologically important ion channels.     

Cx40和Cx43调节大鼠肠系膜上动脉收缩反应性与钙敏感性的机制

目的：研究连接蛋白Cx40/Cx43对大鼠肠系膜上动脉内膜依赖的血管收缩反应性与钙敏感性的调节作用机制。方法:以SD大鼠肠系膜上动脉（SMA）为研究对象，用Cx40或Cx43反义寡脱氧核苷酸（Cx40/Cx43AODN）阻断SMA Cx40或Cx43表达，观察缺氧处理后SMA的收缩反应性、钙敏感性、肌球蛋白轻链磷酸酶/激酶（MLCP/MLCK)的活性、20 kD的肌球蛋白轻链（MLC₂₀）磷酸化程度的变化。结果:Cx40AODN可以降低正常组、1 h和3 h缺氧组SMA MLCP活性，增加MLC₂₀磷酸化水平，改善血管的钙敏感性和内膜依赖的收缩反应性；Cx43AODN可以增加各组血管的MLCP活性，减少MLC₂₀磷酸化水平，降低血管的钙敏感性和内膜依赖的收缩反应性。Cx40和Cx43AODN对SMA MLCK活性无明显作用。结论:Cx40和Cx43主要通过调节血管平滑肌细胞的MLCP活性和MLC₂₀磷酸化水平调节血管的钙敏感性，从而调节休克后内膜依赖的血管收缩反应性。     

急性脑梗塞患者血浆内皮素与血小板内钙含量和聚集关系的探讨

本文用放射免疫分析测定了１６例急性脑梗塞病人的血浆内皮素，用比浊法测定了血小板聚集，用Ｆｕｒａ－２／ＡＭ荧光技术测定了血小板内游离Ｃａ＾２＋含量。急性脑梗塞病人血浆内皮素明显升高（Ｐ〈０．０１），血小板聚集率增设增高（Ｐ〈０．０１），血小板内Ｃａ２＾＋含量增高（Ｐ〈０．０１），且观察到ＡＤＰ诱导的血小板聚集与血小板内Ｃａ＾２＋含量之间呈正相关（ｒ＝０．７８，Ｐ〈０．０１），而血浆内皮素与血小反聚集     

Effects of Na+, K+ and Mg2+ on45Ca2+ uptake by pancreatic islets

Microdissected pancreatic islets of noninbredob/ob-mice were used to study ionic effects on the lanthanum-nondisplaceable⁴⁵Ca²⁺ uptake by islet cells. Omission of Mg²⁺ from the incubation medium had no effect, but the⁴⁵Ca²⁺ uptake was increased by omission of Na⁺ and decreased by omission of K⁺. Excess Mg²⁺ (1.2–15 mM) inhibited and excess K⁺ (4.7–25 mM) stimulated the⁴⁵Ca²⁺ uptake in a concentration-dependent manner. Stimulation of⁴⁵Ca²⁺ uptake in Na⁺-deficient islets was associated with an enhancement of the basal insulin release. Total abolishment of glucose-stimulated⁴⁵Ca²⁺ uptake in K⁺-deficient islets did not preclude a significant secretory response to glucose. It is concluded that the lanthanum-nondisplaceable⁴⁵Ca²⁺ uptake shows a partial correlation to insulin release.