Notice

¹⁷O NMR studies of ¹⁷O enriched water solutions containing superoxide dismutase have been performed between pH 7.5 and 11.7. Whereas T₁ measurements do not reveal any interaction between ¹⁷O and the paramagnetic copper center, the linewidth results appreciably increased with increasing pH with an apparent pK_a of 11.3. Comparison with ¹H NMR relaxation studies allows to interpret the present data as due to binding to the copper ion of an OH^? anion at high pH. The binding position should be of “equatorial” type, not involving the binding position of the coordinated water.     

Desensitization of the human neutrophil degranulation response: Studies with 5,12-dihydroxy-6,8,10,14-eicosatetraenoic acid

The human polymorphonuclear neutrophil degranulation response to 5,12-dihydroxy-6,8,10,14-eicosatetraenoic acid was completely desensitized by preincubating the cells with small amounts of this same fatty acid. Desensitization developed within 1 min, persisted in thoroughly washed cells, and was not due to inactivation of the stimulus. These desensitized cells, however, degranulated partially in response to the ionophore A23187 and normally in response to C5a, N-formyl-methionyl-leucyl-phenylalanine, 1-$\text{0}\text{-}\text{alkyl-2-}\text{0}\text{-}\text{acetyl}\text{-}\text{sn}\text{-}\text{glycero-3-phosphocholine}$, and phorbol myristate acetate. Thus, the dihydroxy fatty acid is a unique stimulus which degranulates and desensitizes neutrophils by pathways at least partially distinct from those utilized by the other stimuli. The fatty acid, although rapidly formed in degranulating neutrophils, is unlikely to be an essential or universal mediator of the degranulation response.     

Microfilament accumulation and the transport of amino acids and glucose in adult rat hepatocytes cultured on collagen gel/nylon mesh

Transport of α-aminoisobutyric acid in cultured hepatocytes is temperature- and energy-dependent, whereas transport of 2-deoxy-D-glucose is not energy-dependent. In early cultures of hepatocytes (day 2) on a collagen gel/nylon mesh, the cells contain few microfilaments and the transport of amino acids and glucose is 5–7 times more than in late cultures of hepatocytes (day 6) which contain an apical, extensive accumulation of microfilaments. Cytochalasin D has little effect on the transport of amino acids and glucose in day 2 cultures of hepatocytes, but enhances transport of both compounds in day 6 cultures. These findings suggest that the microfilament accumulation in cultured hepatocytes inhibits transport of amino acids and glucose.     

Release, purification, and characterization of platelet-activating factor (PAF)

Platelet-activating factor (PAF) is a phospholipid mediator, released by basophils, macrophages and neutrophils under immunological and non immunological stimuli. It aggregates platelets and liberates their vasoactive contents. We studied the "spontaneous" release of PAF from hog blood leukocytes : optimal conditions were 22 degrees C, pH 9.5 in BSA and Ca2+-containing Tyrode's. This release was inhibited by the Ca2+-chelating agent, EDTA, and by the phospholipase A2 inhibitor, bromophenacyl bromide. Disruption of the cells did not yield PAF, indicating that it is not a "preformed" mediator. A preparative procedure for the extraction and purification of bulk quantities of PAF was developed. Purification was performed by silicic acid columns followed by high pressure liquid chromatography. The active fraction was eluted between sphingomyelin and lysophosphatidylcholine. The PAF purest fractions were still contaminated with these phospholipids as shown by thin layer chromatography and chemical ionization mass spectrometry. PAF activity was not affected by treatment with diazomethane, acetylation or hydrogenation. Our results combined with those obtained from our previous studies of the PAF structure using specific phospholipases indicate that PAF is a glycero-phospholipid devoid of ester function at position 1. This allowed us to establish precise criteria to distinguish PAF from other aggregating agents.     

Biologic activity of extracts of delayed hypersensitivity skin reaction sites

Extracts obtained from skin sites of delayed hypersensitivity reactions show chemotactic activity for monocytes and lymphocytes but not neutrophils. The soluble extractable factors present at these sites have in vivo activity as well; they promote the accumulation of monocytes in peritoneal exudates and cause inflammatory reactions in the skin of nonimmunized animals. The skin inflammatory infiltrates are predominantly mononuclear and are similar to those of delayed hypersensitivity reactions in actively immunized guinea pigs. The extracts which produced these effects had no detectable MIF activity, nor permeability inducing activity in excess of that obtainable from normal skin.These monocyte and lymphocyte chemotactic factors were analyzed by sucrose density ultracentrifugation. By this technique the distribution of monocyte factors corresponded rather closely with that of the monocyte chemotactic factors obtained from an antigen-activated lymphocyte culture. Similar correspondence was obtained for the bulk of the lymphocyte chemotactic activity present in skin extracts and in culture supernatants. This suggests the possibility that the lymphokine-like substances in the skin extracts might in fact represent lymphokines. Further documentation of this point will provide a link between in vitro and in vivo manifestations of delayed hypersensitivity.     

Voltage dependence of current through the Na,K-exchange pump ofRana oocytes

Summary We have studied current (I _Str) through the Na, K pump in amphibian oocytes under conditions designed to minimize parallel undesired currents. Specifically,I _Str was measured as the strophanthidin-sensitive current in the presence of Ba^2–, Cd²⁺ and gluconate (in place of external Cl^–). In addition,I _Str was studied only after the difference currents from successive applications and washouts of strophanthidin (Str) were reproducible. The dose-response relationship to Str in four oocytes displayed a meanK _0.5 of 0.4 m, with 2–5 m producing 84–93% pump' block. From baseline data with 12 Na⁺-preloaded oocytes, voltage clamped in the range [–170, +50 mV] with and without 2–5 m Str, the averageI _Str depended directly onV _m up to a plateau at 0 mV with interpolated zero current at –165 mV. In three oocytes, lowering the external [Na⁺] markedly decreased the voltage sensitivity ofI _p , while producing only a small change in the maximal outwardI _Str. In contrast, decreasing the external [K⁺] from 25 to 2.5mm reducedI _Str at 0 mV without substantially affecting its voltage dependence. At K⁺ concentrations of 1mm, both the absolute value ofI _Str at 0 mV and the slope conductance were reduced. In eight oocytes, the activation of the averagedI _Str by [K⁺] _o over the voltage interval [–30, +30 mV] was well fit by the Hill equation, with K=1.7±0.4mm andnH (the minimum number of K⁺ binding sites) =1.7±0.4. The results unequivocally establish that the cardiotonic-sensitive current ofRana oocytes displays only a positive slope conductance for [K⁺] _o >1mm. There is therefore no need to postulate more than one voltage-sensitive step in the cycling of the Na, K pump under physiologic conditions. The effects of varying external Na⁺ and K⁺ are consistent with results obtained in other tissues and may reflect an ion-well effect.     

Ryanodine Inhibits Caffeine-Evoked Ca2+ Mobilization and Catecholamine Secretion from Cultured Bovine Adrenal Chromaffin Cells

The effects of ryanodine, a selective inhibitor of the Ca(2+)-induced Ca2+ release mechanism, on caffeine-evoked changes in cytosolic Ca2+ concentration ([Ca2+]i) and catecholamine secretion were investigated using cultured bovine adrenal chromaffin cells. Caffeine (5-40 mM) caused a concentration-dependent transient rise in [Ca2+]i and catecholamine secretion in Ca2+/Mg(2+)-free medium containing 0.2 mM EGTA. Ryanodine (5 x 10(-5) M) alone had no effect on either [Ca2+]i or catecholamine secretion. Although the application of ryanodine plus caffeine caused the same increase in both [Ca2+]i and catecholamine secretion as those induced by caffeine alone, ryanodine (4 x 10(-7) - 5 x 10(-5) M) irreversibly prevented the increase in both [Ca2+]i and catecholamine secretion resulting from subsequent caffeine application over a range of concentrations. The secretory response to caffeine was markedly enhanced by replacement of Na+ with sucrose in Ca2+/Mg(2+)-free medium, and this enhanced response was also blocked by ryanodine. Caffeine was found to decrease the susceptibility of the secretory apparatus to Ca2+ in digitonin-permeabilized cells. These results indicate that caffeine mobilizes Ca2+ from intracellular stores, the function of which is irreversibly blocked by ryanodine, resulting in the increase in catecholamine secretion in the bovine adrenal chromaffin cell.