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R Ekerdt

Publications and source records attributed to R Ekerdt.

11 recordsLinked to original sources
PubMed1992

Role of prostanoids in the inflammatory reaction and their therapeutic potential in the skin.

Vasodilatory prostaglandins (PG), contributing to the inflammatory reaction, have gained considerable attention. It is becoming apparent that PG have pharmacological effects traceable to biological activities distinct from smooth muscle relaxation. The data from pharmacological experiments presented here indicate the diverse action of vasodilatory PG analogues in the skin of laboratory animals. Nocloprost, a stable PGE2 analogue, induced erythema in intact skin of rats when applied topically and inhibited in the same dose range an irritant-induced inflammatory reaction in the ears of mice. Iloprost, a stable PGI2 analogue, showed proinflammatory activity after local application by enhancing the leukotriene B4 induced cell infiltration in the skin of mice. The attenuation of the spreading of ear necrosis in mice, on the other hand, indicates an anti-ischemic therapeutic potential of iloprost. Research in the past has elucidated the influence of PG on the vascular component of inflammation, but the role of PG on the cellular component of inflammation is less clear. The diverse effects of PG in skin indicate the need for a better understanding of their local actions.

Animals↗
PubMed1982

Synexin facilitates fusion of specific phospholipid membranes at divalent cation concentrations found intracellularly.

The effect of synexin (an adrenal medullary protein) on the kinetics of Ca2+- and Mg2+-mediated membrane fusion was examined. Membrane fusion was studied by monitoring intermixing of the aqueous contents of phospholipid vesicles. Synexin facilitated Ca2+-mediated, but not Mg2+-mediated, fusion of phosphatidate/phosphatidylethanolamine (1:3) and phosphatidate/phosphatidylserine/phosphatidylethanolamine/cholesterol (1:2:3:2) vesicles. The threshold concentration of Ca2+ for fusion was decreased to approximately equal to 10 microM in the presence of synexin at 6 micrograms/ml and 1.5 mM Mg2+ in vesicle suspensions containing 50 microM lipid. This effect of synexin was drastically inhibited by including 25% phosphatidylcholine (mol/mol) in the vesicle membrane. It is proposed that the Ca2+-dependent lipid-specific enhancement of membrane fusion by synexin contributes to an increase in the sensitivity of specific intracellular membranes to Ca2+ with respect to fusion.

Animals↗
PubMed1982

Intermembrane contact affects calcium binding to phospholipid vesicles.

Binding of Ca2+ to liposomes composed of phosphatidylserine (PtdSer) was analyzed by potentiometric titrations. Ca2+ binding to large unilamellar PtdSer vesicles was saturable at a stoichiometry of 1:2 (Ca2+/PtdSer). At approximately 6 X 10(-4) M [Ca2+]free, the binding curve exhibited a discontinuity that can be attributed to the formation of a Ca2+/PtdSer complex with a higher affinity. When both Ca2+ and Mg2+ are present, depending on the relative concentrations, Mg2+ can either complete or can enhance Ca2+ binding. Concomitant to the enhanced binding, the vesicle suspension was found to aggregate, suggesting that close contact of membranes is a prerequisite for the abrupt change in affinity. This concept was tested by binding studies with liposomes of mixed composition. It was found that the incorporation of 50 mol% phosphatidylethanolamine (PtdEtn) into PtdSer liposomes produced a similar binding pattern to that of pure PtdSer with a saturable stoichiometry of 1:2 (Ca2+/PtdSer). However, incorporation of 50 mol% phosphatidylcholine (PtdCho) completely abolished the discontinuous shift in affinity and apparent saturation was reached at a stoichiometry of 1:4 (Ca2+/PtdSer). In addition, Ca2+ binding to PtdSer liposomes with 10 mol% galactosylcerebroside was not altered when compared to pure PtdSer, whereas 10 mol% of the glycolipid GL-4 abolished the increased binding. The results are closely correlated with recent findings on the role of the membrane composition in Ca2+-induced fusion of liposomes and argue in favor of a specific Ca2+/PtdSer complex (with 1:2 stoichiometry) forming only at points of close contact between membranes and serving as the trigger for membrane fusion.

Calcium↗
PubMed1981

Latent acetylcholinesterase in secretory vesicles isolated from adrenal medulla.

A new procedure is described for the preparation of highly purified and stable secretory vesicles from adrenal medulla. Two forms of acetylcholinesterase, a membrane bound form as well as a soluble form, were found within these vesicles. The secretory vesicles, isolated by differential centrifugation, were further purified on a continuous isotonic Percoll gradient. In this way, secretory vesicles were separated from mitochondrial, microsomal and cell membrane contamination. The secretory vesicles recovered from the gradient contained an average of 2.26 mumol adrenaline/mg protein. On incubation for 30 min at 37 degrees C in media differing in ionic strength, pH, Mg2+ and Ca2+ concentration, the vesicles released less than 20% of total adrenaline. Acetylcholinesterase could hardly be detected in the secretory vesicle fraction when assayed in isotonic media. However, in hypotonic media (less than 400 mosmol/kg) or in Triton X-100 (0.2% final concentration) acetylcholinesterase activity was markedly higher. During hypotonic treatment or when secretory vesicles were specifically lyzed with 2 mM Mg2+ and 2 mM ATP, adrenaline as well as part of acetylcholinesterase was released from the vesicular content. On polyacrylamide gel electrophoresis this soluble enzyme exhibited the same electrophoretic mobility as the enzyme released into the perfusate from adrenal glands upon stimulation. In addition to the soluble enzyme a membrane bound form of acetylcholinesterase exists within secretory vesicles, which sediments with the secretory vesicle membranes and exhibits a different electrophoretic mobility compared to the soluble enzyme. It is concluded, that the soluble enzyme found within isolated secretory vesicles is secreted via exocytosis, whilst the membrane-bound form is transported to the cell membrane during this process, contributing to the biogenesis of the cell membrane.

Acetylcholinesterase↗
PubMed1980

The role of Ca2+ as a trigger for membrane fusion.

As revealed by freeze-fracturing, secretory vesicles isolated from pancreatic islet cells fuse when incubated with low concentration of Ca2+. The properties of this process are described and were found to be similar to those investigated with isolated secretory vesicles from different tissue origin. Secretory vesicle fusion is compared mainly with the ionic requirements of insulin secretion by the pancreatic B-cells and exocytosis by other secretory cells.

Calcium↗