Subject(s)
Anemia, Hemolytic, Autoimmune/complications , Polyradiculoneuropathy, Chronic Inflammatory Demyelinating/complications , Aged, 80 and over , Anemia, Hemolytic, Autoimmune/diagnosis , Anemia, Hemolytic, Autoimmune/drug therapy , Glucocorticoids/therapeutic use , Humans , Male , Polyradiculoneuropathy, Chronic Inflammatory Demyelinating/diagnosis , Polyradiculoneuropathy, Chronic Inflammatory Demyelinating/drug therapy , Prednisone/therapeutic useABSTRACT
We examined the ionic mechanisms underlying the responses of canine trachealis to superoxide (generated in vitro by using xanthine oxidase or added exogenously) and peroxide (generated spontaneously in vitro by the dismutation of superoxide or added exogenously). Although neither had any effect on resting tone, both triggered relaxations in carbachol-precontracted tissues. These relaxations were eliminated by catalase but were much less sensitive to the hydroxyl radical scavenger dimethylthiourea, indicating they were mediated primarily by peroxide. These relaxations were decreased in magnitude and/or slowed by nifedipine (10(-6) M), ouabain (10(-6) M), or tetraethylammonium (25 mM), but not by 4-aminopyridine (5 mM), and were small or absent in tissues precontracted with 30 mM KCl. Finally, peroxide triggered membrane hyperpolarization and elevated cytosolic concentration of Ca(2+) (primarily via release from the internal store). Thus peroxide-mediated relaxations seem to involve Ca(2+) release, opening of Ca(2+)-dependent K(+) channels, hyperpolarization, closure of Ca(2+) channels, and relaxation. In addition, some other free radical (hydroxyl radical?) may activate the Na(+)-K(+) pump, also hyperpolarizing the membrane and causing relaxation.
Subject(s)
Hydrogen Peroxide/pharmacology , Muscle Relaxation/drug effects , Potassium Channels/metabolism , Sodium-Potassium-Exchanging ATPase/metabolism , Superoxides/pharmacology , Trachea/drug effects , Animals , Calcium/metabolism , Calcium/physiology , Dogs , Dose-Response Relationship, Drug , Enzyme Inhibitors/pharmacology , Free Radical Scavengers/pharmacology , Free Radicals/metabolism , Free Radicals/pharmacology , Hydrogen Peroxide/metabolism , In Vitro Techniques , Membrane Potentials/drug effects , Muscle Relaxation/physiology , Muscle Tonus/drug effects , Muscle Tonus/physiology , Muscle, Smooth/cytology , Muscle, Smooth/drug effects , Muscle, Smooth/physiology , Nifedipine/pharmacology , Ouabain/pharmacology , Sodium-Potassium-Exchanging ATPase/antagonists & inhibitors , Superoxides/metabolism , Tetraethylammonium/pharmacology , Thiourea/analogs & derivatives , Thiourea/pharmacology , Trachea/physiology , Xanthine/metabolism , Xanthine/pharmacology , Xanthine Oxidase/metabolism , Xanthine Oxidase/pharmacologyABSTRACT
We examined cytosolic concentration of Ca2+ ([Ca2+]i) in canine airway smooth muscle using fura 2 fluorimetry (global changes in [Ca2+]i), membrane currents (subsarcolemmal [Ca2+]i), and contractions (deep cytosolic [Ca2+]i). Acetylcholine (10(-4) M) elicited fluorimetric, electrophysiological, and mechanical responses. Caffeine (5 mM), ryanodine (0.1-30 microM), and 4-chloro-3-ethylphenol (0.1-0.3 mM), all of which trigger Ca2+-induced Ca2+ release, evoked Ca2+ transients and membrane currents but not contractions. The sarcoplasmic reticulum (SR) Ca2+-pump inhibitor cyclopiazonic acid (CPA; 10 microM) evoked Ca2+ transients and contractions but not membrane currents. Caffeine occluded the response to CPA, whereas CPA occluded the response to acetylcholine. Finally, KCl contractions were augmented by CPA, ryanodine, or saturation of the SR and reduced when SR filling state was decreased before exposure to KCl. We conclude that 1) the SR forms a superficial buffer barrier dividing the cytosol into functionally distinct compartments in which [Ca2+]i is regulated independently; 2) Ca2+-induced Ca2+ release is preferentially directed toward the sarcolemma; and 3) there is no evidence for multiple, pharmacologically distinct Ca2+ pools.
