PubMed · 7272335
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L Vassilev, G Russev. 1981. Ion activity decrease in the presence of sucrose.. https://doi.org/10.1016/0304-4165(81)90229-4
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The i.v. administration of calcium before or shortly after treatment of supraventricular tachycardia with verapamil has been suggested to counteract a hypotensive response to verapamil. We discuss the case of a patient who presented to the emergency department with an accelerated wide-complex tachycardia and minimal symptoms. Immediately after i.v. administration, of 1 g calcium chloride as pretreatment for verapamil administration, ventricular fibrillation developed. Emergency physicians should be aware of potential dangers after the administration of i.v. calcium preparations when trying to prevent known hypotensive side effects of i.v. verapamil administration.
The effects of phospholipid vesicles and their fatty acid compositions on the acceleration of Protein C activation by thrombin-thrombomodulin was studied in vitro. Four main phospholipid fractions were prepared from cultured human umbilical vein endothelial cells, and purified thrombomodulin from human placenta was reconstituted into vesicles consisting of phosphatidylcholine (PtdCho) alone, PtdCho plus phosphatidylethanolamine (PtdEtn), PtdCho plus phosphatidylserine (PtdSer) and PtdCho plus PtdIns (1:1, w/w in each case). Vesicles of PtdCho, PtdIns/PtdCho, PtdSer/PtdCho and PtdEtn/PtdCho increased thrombin-thrombomodulin-catalysed protein C activation by 1.2-, 1.9-, 4.3- and 8.4-fold respectively compared with that in the absence of phospholipid. This Protein C activation was not affected by distearoyl PtdEtn/distearoyl PtdCho, whereas it was markedly increased with increasing content of unsaturated fatty acid in PtdEtn. The thrombin-dependent Protein C activation by thrombomodulin reconstituted into dilinolenoyl PtdEtn/distearoyl PtdCho was 14.6 times that by thrombomodulin reconstituted into distearoyl PtdEtn/distearoyl PtdCho, as a result of a decrease in the dissociation constant (Kd) for thrombin and the Michaelis constant (Km) for Protein C of thrombomodulin. Binding of Protein C to PtdEtn/PtdCho fixed to a microwell plate required the presence of CaCl2 and increased with increasing degree of unsaturation of fatty acid in PtdEtn. As PtdEtn appeared on the outside of the plasma membrane in cultured human umbilical vein endothelial cells after thrombin stimulation, it was presumed that Protein C activation could be elevated by PtdEtn at the outer surface of the plasma membrane via an increased affinity between thrombomodulin, thrombin and Protein C, resulting from both increased formation of the thrombin-thrombomodulin complex via a conformational change in thrombomodulin and increased binding of Protein C to the membrane phospholipid in a Ca(2+)-dependent manner.
Ultrafast computed tomography (UFCT) has the potential to quantify coronary hydroxyapatite (HAP). However, no definitive studies validating this technique are available. We constructed a human chest phantom model with coronary arteries represented by cylindrical holes containing: (1) calcium chloride solutions, (2) a block of HAP immersed in paraffin (without partial volume effect), and (3) HAP granules embedded in a gelatin matrix (with partial volume effect). We scanned this model to determine the relationship between measured CT number per voxel and density of the calcium per voxel. The relationships between CT number and concentration of calcium chloride was linear (r = 0.992 to 0.999). Using a commercially available standard bone mineral phantom, we were able to estimate the concentration of HAP to an accuracy from 94 to 97% when partial volume effects were absent. However, when partial volume effects were present, two methods of estimating HAP produced significant errors (1 to 384%, and 17 to 52%). We conclude that significant partial voluming errors degrade the accuracy of HAP quantitation and that further evaluation and corrections are needed before such quantitation is clinically applied.