Anesthetic drugs have complex effects on airway function. These actions have the potential for both benefit (e.g., relief of bronchospasm in asthmatic patients) and harm (e.g., interference with normal mechanisms that match ventilation to perfusion in the lung). The overall goal of this research program is to continue the study of how anesthetics affect these airways. Prior work has shown that these drugs relax airway smooth muscle (AWSM) by depressing neural pathways innervating the smooth muscle cell (neural effects) and by affecting the smooth muscle cell itself (a direct effect). The goal of this proposal is to elucidate mechanisms responsible for this direct effect.
Two specific aims will be pursued, concentrating on the actions of halothane and ketamine, two drugs currently recommended in the management of asthmatic patients, as representative anesthetic agents. Reductions in the concentration of cytosolic calcium ([Ca2+]i), an important mediator of AWSM contraction, may play a key role in anesthetic effects.
AIM A will explore mechanisms related to this action in isolated canine and human AWSM preparations by measuring [Ca2+]i, extracellular calcium influx, and the release of calcium from intracellular stores. Anesthetics may also decrease the amount of force produced for a given [Ca2+]i (i.e., decrease the """"""""calcium sensitivity"""""""" of the myofibrillar contractile system).
AIM B will examine mechanisms responsible for this effect. Permeabilized AWSM preparations, in which [Ca2+]i can be held constant by controlling extracellular calcium concentration, will be used to investigate these calcium-independent actions. Experiments will determine which of the systems that regulate calcium sensitivity is affected by anesthetics. Measurements of smooth muscle mechanics will provide insight into anesthetic effects on actin-myosin crossbridge kinetics. It is hypothesized that anesthetics affect both [Ca2+]i and calcium sensitivity, and that the relative importance of each of these mechanisms depends on the type and intensity of AWSM membrane receptor stimulation, the timing of anesthetic administration, and the specific anesthetic agent. An understanding of the complex mechanisms producing these effects may guide the proper application of these drugs in the perioperative period, and may also provide insights into general mechanisms of anesthetic actions in other tissues, as many of the intracellular signal transduction pathways found in AWSM are common to other cell types. In addition, these anesthetics may have unique mechanisms of action in AWSM which may suggest strategies for the future development of therapeutic bronchodilators.
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