Effect of Voltage-Sensitive Calcium Channel Antagonists on the Release of 5-Hydroxytryptamine from Rat Hippocampus In Vivo

The effect of calcium channel antagonists on the release of 5-hydroxytryptamine from the hippocampus of the chloral hydrate-anaesthetised rat was studied using the technique of intracerebral microdialysis. As the basal concentration of 5-hydroxytryptamine was close to the limit of detection of the HPLC method (8 fmol), the 5-hydroxytryptamine reuptake inhibitor, fluoxetine (10 microM), was included in the perfusion fluid. The L-type voltage-sensitive calcium channel antagonists, PN200-110, diltiazem, and verapamil, all passed through the dialysis membrane, giving a recovery of 20-30%. The N-type voltage-sensitive calcium channel antagonist, omega-conotoxin, penetrated less readily (12% recovery). The dihydropyridine, PN200-110, adhered to the probe, resulting in an effective concentration at the membrane 30% of that in the perfusion fluid. The concentration of 5-hydroxytryptamine in the dialysate samples was reduced by 60% in the absence of calcium. The L channel antagonists had little effect on the release of 5-hydroxytryptamine, which was inhibited, in a dose-dependent manner, to a maximum of 40% by omega-conotoxin. It is concluded that, under physiological conditions, the release of 5-hydroxytryptamine from the rat hippocampus is dependent on the entry of calcium through N-type voltage-sensitive calcium channels, although another calcium channel may also be involved.     

溴化马来松香的合成、表征及其阻燃性的研究

本文以马来松香与液溴加成,合成了溴化马来松香;研究了反应温度、原料的摩尔比、反应时间等因素对反应过程及产物性能的影响.用FT-IR、1H NMR和TG对溴化马来松香进行了表征.结果表明,当反应温度为-2～6℃,反应时间5～6 h,反应物的当量配比约为1.2时,收率可达87.9%.溴化马来松香具有较好的阻燃性,同时也拓宽了松香的应用范围,提高了松香的附加值.     

Predicting Carbon and Nutrient Transformations in Tidal Freshwater Wetlands of the Hudson River

The exchange of water between the main channel of the tidal freshwater Hudson River and its tidal wetlands is a large proportion of the whole-river water volume and causes large changes in concentrations of some dissolved and suspended constituents. Ten representative wetlands were assessed for their ability to alter quantities of inorganic nutrients, suspended particles, dissolved organic carbon (DOC), and dissolved oxygen during tidal exchange. The majority of sites acted as sinks for oxygen and nitrate and as sources of DOC. For other variables such as phosphate and pigments, individual wetlands varied broadly in both the direction and magnitude of change. For some variables (oxygen, DOC) we found mechanistically plausible predictors for the magnitude of alteration. The proportional coverage of submerged vegetation or intertidal marsh graminoid vegetation was related to the degree of change in oxygen and DOC. For most cases, however, we did not find strong predictors and we attribute this to the spatial positioning of “hot spots” or redundancy in the processes actually responsible for the transformation. Our ability to predict ecosystem performance from whole-ecosystem attributes may be impeded by lack of consideration of within-system spatial contingencies or lack of knowledge of which process is actually responsible for the observed alteration in material flux.     

Calcitonin receptors in a cloned human breast cancer cell line (MCF 7)

A human breast cancer cell line, MCF 7, is shown to possess a specific calcitonin receptor and calcitonin responsive adenylate cyclase, and calcitonin treatment results in activation of cyclic AMP-dependent protein kinase. Studies with several analogues of calcitonin show that the receptor and adenylate cyclase response preserve the ability to discriminate among the structure-function relationships of the calcitonin molecule. The same cell line has been shown recently to possess a receptor for the steroid hormone, 1,25(OH)₂-vitamin D. Coexistence in MCF 7 cells of receptors for two calcium-regulating hormones may be related to the osteoclast-like properties of these cells.     

Acetylcholine-evoked uncoupling restricts the passage of Lucifer Yellow between pancreatic acinar cells

Summary Direct cell to cell movement of the fluorescent dye Lucifer Yellow CH (457 daltons) in exocrine acinar tissue is demonstrated by direct observation of living mouse pancreatic segments. Electrical uncoupling of pancreatic acinar cells by local application of a high concentration of acetylcholine significantly restricts cell to cell passage of the fluorescent dye. This result shows that a secretagogue can control direct movement of organic molecules between cells through junctional channels.