No abstract is provided for this article.
No abstract is provided for this article.
EditorialCalcium-channel blockers and asthma The concentration of free calcium ions (Ca++) in the cytoplasm regulates many aspects of cell function, including muscle contraction and the secretion of mediators, neurotransmitters and hormones.Con- traction of airway smooth muscle, secretion of mast cell mediators and mucus, and vagal neurotransmis- sion, all of which may be increased in asthma, are dependent on movement of Ca++ into the cell.This raises the possibility that an increase in Ca++ flux may be a fundamental abnormality in asthma and might be an explanation for bronchial hyperreactivity.'The development of drugs that interfere with the entry of Ca++ into cells has now made it possible to study the role of Ca++ in disease, and these drugs are widely used in the treatment of cardiovascular disease.There has recently been increasing interest in the use of calcium-channel blockers in asthma, not because of their therapeutic potential but because of what they may reveal about underlying mechanisms. CALCIUM IONS AND CELL FUNCTIONThe concentration of free intracellular Ca++ in rest- ing cells is approximately 0-1 ,moIIl, whereas that in extracellular fluid is 1 mmo0l/;2 3 and recent studies using bioluminescent indicators of free intracellular Ca++ have found that the Ca++ concentration increases 100-fold after cell activation.45When intracellular Ca++ rises to a critical concentration (about 1 ,umol/l) it binds to a specific binding protein called calmodulin, which then activates the specific kinase and enzyme system that brings about the response, such as contraction or secretion.This increase in cytoplasmic Ca++ is derived from extracellular Ca`+ or intracellular stores (mainly sarcoplasmic reticulum), or both.Indeed, the entry of Ca++ into the cell may trigger the release of Ca++ from intracellular stores.The source of Ca++ required for the cellular response may differ from tissue to tissue.The cell membrane itself is impermeable to Ca++ and Ca++ moves into the cell through specific channels.These are macromolecular structures traversing the membrane
Based on data described previously, the wallstent is a versatile stent that, by virtue of its longitudinal flexibility and low profile, can be deployed with a high degree of success in complex lesions of both native coronary arteries and bypass vein grafts. This article discusses its structural design, the experimental studies of thrombogenicity and polymeric coating, early and late clinical experience with the wallstent, clinical evaluation of the less shortening wallstent, and the current indications of the coronary wallstent.
