Effects of alkaline pH on sarcoplasmic reticulum Ca2+ release and Ca2+ uptake.

Alkalinization-induced Ca2+ release from isolated frog or rabbit sarcoplasmic reticulum vesicles appears to consist of two distinct components: 1) a direct activation of ruthenium red-sensitive Ca2+ release channels in terminal cisternae and 2) an increased ruthenium red-insensitive Ca2+ efflux through some other efflux pathway distributed throughout the sarcoplasmic reticulum. The first of these releases exhibits an alkalinization-induced inactivation process and does not depend on the ruthenium red-insensitive form of Ca2+ release as a triggering agent for secondary Ca(2+)-induced Ca2+ release. Both releases are inhibited when the extravesicular (i.e. cytoplasmic) free [Ca2+] is reduced. This may reflect an increased sensitivity of the Ca2+ release channels to Ca2+ at alkaline pH. The pH sensitivity of the ruthenium red-sensitive Ca2+ release channels could be of significance during excitation-contraction coupling. The ruthenium red-insensitive form of Ca2+ release is less likely to be physiologically relevant, but it probably has contributed greatly to reports of alkalinization-induced decreases in net sarcoplasmic reticulum Ca2+ uptake, particularly under conditions where oxalate supported Ca2+ uptake is much less affected, as here.     

Drug-induced Ca2+ release from isolated sarcoplasmic reticulum. II. Releases involving a Ca2+-induced Ca2+ release channel

Calcium ions that have been preloaded into isolated sarcoplasmic reticulum subfractions in the presence of ATP and pyrophosphate may be released upon addition of a large number of diverse pharmacologic substances. We report here that not only caffeine, but also Ca2+ ions, thymol, quercetin, menthol, halothane, chloroform, 1-ethyl-2-methylbenzimidazole, ryanodine, tetraphenylboron, ketoconazole, miconazole, clotrimazole, W-7, doxorubicin, 5,5'-dithiobis-(2-nitrobenzoic acid), p-chloromercuribenzoic acid, and low concentrations of Ag+ induce Ca2+ release from such triadic sarcoplasmic reticulum. All these drugs induce increased undirectional Ca2+ efflux. We believe all these drug-induced Ca2+ releases are mediated by Ca2+ efflux through the same ion channel since these releases are all greatly attenuated when light sarcoplasmic reticulum is substituted for triads and are even more pronounced when transverse tubule-free terminal cisternae are substituted for triads, and all these forms of drug-induced Ca2+ release are inhibited by submicromolar concentrations of ruthenium red, and by submillimolar concentrations of tetracaine, 9-aminoacridine, and Ba2+, yet they are not affected by nifedipine even at a concentration of 50 microM.     

下丘脑外侧区注射TRH对大鼠胃酸分泌的影响

本文采用连续收集胃腔灌流法,观察下丘脑外侧区(LHA)注射促甲状腺激素释放激素(TRH)对大鼠胃酸分泌的影响,并分析TRH在LHA促进胃酸分泌的作用机制。结果表明:(1)LHA注射TRH(1μg)明显地刺激胃酸分泌;(2)预先向LHA注射酚妥拉明(10μg)、美多心安(5μg)及胃泌素抗体1μl(1:640)并不影响TRH的泌酸作用,如预先向LHA注射阿托品(5μg)则可消除TRH的泌酸效应;(3)垂体摘除及肾上腺切除均不影响TRH的泌酸作用;(4)隔下迷走神经切断后,LHA注入TRH的泌酸效应仍然出现,但持续时间显著缩短;腹腔交感神经节摘除后,TRH仍能促进胃酸分泌,但分泌量少而平稳。以上结果提示:LHA是TRH中枢泌酸效应的有关结构之一,其中枢机制是通过胆碱能M受体中介的,腹腔交感神经节和膈下迷走神经是TRH泌酸效应的传出途径。前者引起的泌酸反应出现较早且引起泌酸高峰,但持续时间短;后者则引起低平的持续分泌。     

Binding and transcytosis of glycoalbumin by the microvascular endothelium of the murine myocardium: evidence that glycoalbumin behaves as a bifunctional ligand

The binding and transport of glycoalbumin (gA) by the endothelium of murine myocardial microvessels were studied by perfusing in situ 125I-gA or gA-gold complexes (gA-Au) and examining the specimens by radioassays and EM, respectively. After a 3-min perfusion, the uptake of radioiodinated gA is 2.2-fold higher than that of native albumin; it is partially (approximately 55%) competed by either albumin or D-glucose, and almost completely abolished by the concomitant administration of both competitors or by gA. D-mannose and D-galactose are not effective competitors. Unlike albumin-gold complexes that bind restrictively to plasmalemmal vesicles, gA-Au labels the plasma-lemma proper, plasmalemmal vesicles open on the lumen, and most coated pits. Competing albumin prevents gA-Au binding to the membrane of plasmalemmal vesicles, while glucose significantly reduces the ligand binding to plasmalemma proper. Competition with albumin and glucose gives additive effects. Transcytosis of gA-Au, already detected at 3 min, becomes substantial by 30 min. No tracer exit via intercellular junctions was detected. gA-Au progressively accumulates in multivesicular bodies. The results of the binding and competition experiments indicate that the gA behaves as a bifunctional ligand which is recognized by two distinct binding sites: one, located on the plasma membrane, binds as a lectin the glucose residues of gA; whereas the other, confined to plasmalemmal vesicles, recognizes presumably specific domains of the albumin molecule.     

中华白蛉的自育性研究

现场及实验室结果表明,我国黄土高原的大多数中华白蛉(Phlebotomus chinensis)应属自育性品系,它通常在羽化后、吸血前经交配能依靠腹节内脂肪体发育卵泡,一般在产卵后始行吸血。其生理性状是:胃内无血、腹节内有大量块状或条状脂肪体。羽化24小时后,附腺内有暗色颗粒,卵巢内有发育的卵泡。在25℃士1℃下它的生活史分快、慢两型。快型从卵至成虫仅需44—50夭,慢型需要以四龄幼虫滞育,其长短随滞育期而定,最长的滞育期达301天。观察了白蛉幼虫在饥饿状态下对自育性的影响。此外,还比较了吸血白蛉与自育性白蛉的妊卵数。吸血白蛉的妊卵数约较自育性的高出1/5。这种自育性品系的中华白蛉在自然居群约内占92%、主要栖于洞穴内为野栖种类。本文对自育性中华白蛉的生态及其防制策略作了分析和讨论。     

Morphology of isolated triads

The triad is the junctional association of transverse tubule with sarcoplasmic reticulum terminal cisternae. A procedure for the isolation of highly enriched triads from skeletal muscle has been described in the previous paper. In the present study, the structural features of isolated triads have been examined by thin-section, negative-staining, and freeze-fracture electron microscopy. In isolated triads, key features of the structure observed in situ have been retained, including the osmiophilic "feet," junctional structures between the transverse tubule and terminal cisternae. New insight into triad structure is obtained by negative staining, which also enables visualization of feet at the junctional face of the terminal cisternae, whereas smaller surface particles, characteristic of calcium pump protein, are not visualized there. Therefore, the junctional face is different from the remainder of the sarcoplasmic reticulum membrane. Junctional feet as viewed by thin section or negative staining have similar periodicity and extend approximately 100 A from the surface of the membrane. Freeze-fracture of isolated triads reveals blocklike structures associated with the membrane of the terminal cisternae at the junctional face, interjunctional connections between the terminal cisternae and t-tubule, and intragap particles. The intragap particles can be observed to be closely associated with the t-tubule. The structure of isolated triads is susceptible to osmotic and salt perturbation, and examples are given regarding differential effects on transverse tubules and terminal cisternae. Conditions that adversely affect morphology must be considered in experimentation with triads as well as in their preparation and handling.     

Purification of morphologically intact triad structures from skeletal muscle

A procedure has been devised for isolation of triads (t-tubule/sarcoplasmic reticulum (SR) junctional complexes) from rabbit skeletal muscle. The procedure consists of preparation of a heavy microsomal fraction followed by two sequential 90-min sucrose gradient centrifugations to enrich the triads. A pyrophosphate/phosphate/magnesium buffer system was introduced to decrease aggregation in order to achieve effective separation. The preparation time is 12 h. Some differences between purified triads isolated by two variants of this method are noted. The purity of the triad fractions has been estimated by particle counting to be in the vicinity of 50%. There is good retention of morphology and Ca++-loading activity and enrichment in Na+,K+-ATPase and adenylate cyclase. The triads are practically devoid of contractile elements, mitochondria, and free plasmalemma, and low in content of light SR. The method for obtaining enriched triads is reproducible, and sufficient yields are obtained for structural, biochemical, and functional characterization.     

COMPOSITION OF CELLULAR MEMBRANES IN THE PANCREAS OF THE GUINEA PIG : II. Lipids

The lipid composition of rough and smooth microsomal membranes, zymogen granule membranes, and a plasmalemmal fraction from the guinea pig pancreatic exocrine cell has been determined. As a group, membranes of the smooth variety (i.e., smooth microsomes, zymogen granule membranes, and the plasmalemma) were similar in their content of phospholipids, cholesterol and neutral lipids, and in the ratio of total lipids to membrane proteins. In contrast, rough microsomal membranes contained much less sphingomyelin and cholesterol and possessed a smaller lipid/protein ratio. All membrane fractions were unusually high in their content of lysolecithin (up to ~20% of the total phospholipids) and of neutral lipids, especially fatty acids. The lysolecithin content was shown to be due to the hydrolysis of membrane lecithin by pancreatic lipase; the fatty acids, liberated by the action of lipase on endogenous triglyceride stores, are apparently scavenged by the membranes from the suspending media. Similar artifactually high levels of lysolecithin and fatty acids were noted in hepatic microsomes incubated with pancreatic postmicrosomal supernatant. E 600, an inhibitor of lipase, largely prevented the appearance of lysolecithin and fatty acids in pancreatic microsomes and in liver microsomes treated with pancreatic supernatant.