84 research outputs found
Differential release of histamine and prostaglandin D2 in rat peritoneal mast cells: roles of cytosolic calcium and protein tyrosine kinases
AbstractWe studied how the release of histamine and prostaglandin D2 (PGD2) were connected in stimulated rat peritoneal mast cells, and to what extent these processes were controlled by the cytosolic Ca2+ concentration, [Ca2+]i, and protein tyrosine kinases. In the presence of 1 mM CaCl2, the G-protein activating compound 48/80 (10 μg/ml) evoked a transient rise in [Ca2+]i and a relatively high secretion of histamine, but only a low release of PGD2. In contrast, 5 μM thapsigargin (an inhibitor of endomembrane Ca2+-ATPases) and 5 μM ionomycin evoked high and prolonged rises in [Ca2+]i, and stimulated the cells to release relatively small amounts of histamine and high amounts of PGD2. Stimulation of the cells with CaCl2 and 10 μM ATP4− gave only minor quantities of histamine and PGD2, despite of the micromolar level of [Ca+]i reached. When CaCl2 was replaced by EGTA, rises in [Ca2+]i as well as release of histamine and PGD2 were reduced with each agonist, but the preference of agonists to release more histamine or PGD2 remained unchanged. In mast cells with depleted Ca2+ stores, the addition of CaCl2 stimulated the store-regulated Ca2+ entry resulting in a prolonged rise in [Ca2+]i. However, simultaneous addition of compound 48/80 and CaCl2 was required for release of histamine and PGD2. In cells with full stores, PGD2 release evoked by compound 48/80 was greatly reduced by genistein and methyl-2,5-dihydroxycinnamate, two structurally unrelated inhibitors of protein tyrosine kinases, whereas histamine secretion was not influenced by these inhibitors. Similarly, with thapsigargin or ionomycin as agonist, PGD2 release was more sensitive to the tyrosine kinase inhibitors than histamine secretion. We conclude that in activated rat peritoneal mast cells: (i) the influx of extracellular Ca2+ potentiates agonist-evoked rises in [Ca2+]i as well as histamine secretion and PGD2 release; (ii) the amplitude of the [Ca2+]i rise does not determine the preferential effect of agonists to release more histamine or more PGD2; (iii) the relatively high PGD2 release evoked by thapsigargin and ionomycin is probably due to their potency to evoke a prolonged rise in [Ca2+]i and to activate protein tyrosine kinases
System identification to analyse changed kinetics of SERCA in intact rat heart
A mechanistic-based model has been derived of calcium handling in the intact heart. This model incorporates the quantitatively most important processes involved in beat-to-beat calcium homeostasis. Based on a priori physiological information the model has been reduced to yield (kinetic) parameters that could be estimated using time-series data of the free calcium concentration in the sarcoplasma. Observations of the dynamics of the overall system were translated into the underlying mechanisms. Experiments in which the most important calcium extrusion pump (Sarcoplasmic Reticulum Ca 2+ -ATPase, SERCA) was disturbed have been successfully analysed and interpreted using model and identification
Evolution of the family of intracellular lipid binding proteins in vertebrates
Members of the family of intracellular lipid binding proteins (iLBPs) have been implicated in cytoplasmic transport of lipophilic ligands, such as long-chain fatty acids and retinoids. iLBPs are low molecular mass proteins (14-16kDa) sharing a common structural fold. The iLBP family likely arose through duplication and diversification of an ancestral iLBP gene. Phylogenetic analysis undertaken in the present study indicates that the ancestral iLBP gene arose after divergence of animals from fungi and plants. The first gene duplication was dated around 930 millions of years ago, and subsequent duplications in the succeeding 550 millions of years gave rise to the 16 iLBP types currently recognized in vertebrates. Four clusters of proteins, each binding a characteristic range of ligands, are evident from the phylogenetic tree. Evolution of different binding properties probably allowed cytoplasmic trafficking of distinct ligands. It is speculated that recruitment of an iLBP during evolution of animals enabled the mitochondrial oxidation of long-chain fatty acid
Dimensions of compartments and membrane surfaces in the intact rabbit heart of importance in studies on intramyocardial transfer of blood-borne substances
Cardiac studies on the uptake, storage and
intramyocardial transfer of blood-borne substances
require detailed information on the geometric
ultrastructural dimensions of myocardial compartments
and parts thereof, and the membranes separating these
compartments. Such a specific ultrastructural set of data
of the heart is yet lacking. In the present study, we
quantitatively assessed these dimensions in
glutaraldehyde-perfusion fixed rabbit hearts by means of
histological and tailored mathematical techniques.
We showed the true ellipsoid nature of the
myocardial capillary cross section and estimated the
mean capillary diameter dcap. After correction for the
ellipsoid shape, dcap was found to be 5.21±1.41 μm.
Effective widths of the endothelial cell and the
pericapillary interstitium (is1), dimensions of importance
in diffusion, amounted to 187±7 and 160±10 nm,
respectively. The fractional volume of the large vessels
(arteries and veins larger than 10 µm), capillaries,
endothelium, is1, cardiomyocytes, non-pericapillary
interstitium is2, t-tubular compartment and interstitial
cells amounted on average to 5.92%, 9.36%, 1.83%,
1.94%, 73.07%, 5.97%, 0.95% and 0.96%, respectively,
of total myocardial volume, defined as the cardiac tissue
volume, the large blood vessels included. Normalized to
total myocardial volume, the surface area of the luminal
and abluminal endothelial membranes and of the
cardiomyocyte membrane opposing the endothelial cells
amounted to 75.2±5.5x103, 82.2±6.0x103 and
89.1±6.5x103 m2/m3, respectively.
The present study provides quantitative information
about ultrastructural dimensions of the adult rabbit heart,
among others, of importance for studies on cardiac
uptake, and intramyocardial transfer and storage of
blood-supplied substances
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