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  • 1
    ISSN: 1432-2013
    Keywords: Airway smooth muscle ; Patch-clamp ; Ca2+-activated K+ channels ; ATP sensitivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Large-conductance Ca2+-activated K+ channels were studied in membranes of cultured rabbit airway smooth muscle cells, using the patch-clamp technique. In cell-attached recordings, channel openings were rare and occurred only at very positive potentials. Bradykinin (10 μM), an agonist which releases Ca2+ from the sarcoplasmic reticulum, transiently increased channel activity. The metabolic blocker 2,4-dinitrophenol (20 μM), which lowers cellular adenosine triphosphate (ATP) levels, induced a sustained increase of channel activity in cell-attached patches. In excised patches, these channels had a slope conductance of 155 pS at 0 mV, were activated by depolarization and by increasing the Ca2+ concentration at the cytoplasmic side above 10−7 mol/l. ATP, applied to the cytoplasmic side of the patches, dose-dependently decreased the channel's open-state probability. An inhibition constant (K i) of 0.2 mmol/l was found for the ATP-induced inhibition. ATP reduced the Ca2+ sensitivity of the channel, shifting the Ca2+ activation curve to the right and additionally reducing its steepness. Our results demonstrate that cytoplasmic ATP inhibits a large-conductance Ca2+-activated K+ channel in airway smooth muscle. This ATP modulation of Ca2+-activated K+ channels might serve as an important mechanism linking energy status and the contractile state of the cells.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-8744
    Keywords: Nitroglycerin ; dinitrate metabolites ; 1,2-glyceryl dinitrate ; 1,3-glyceryl dinitrate ; pharmacodynamics ; metabolite inhibition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Studies were carried out in conscious dogs to determine the effects of 1,2-glyceryl dinitrate (1,2-GDN) and 1,3-glyceryl dinitrate (1,3-GDN) on nitrogtycerin (GTN) pharmacokinetics and pharmacodynamics. In the first set of experiments, steady state plasma levels (Css) of either 1,2-GDN or 1,3-GDN in three dogs were rapidly achieved by giving an iv bolus (77 μg/kg), followed immediately by an infusion (50 μg/min) of the same GDN. A single iv bolus dose of GTN (0.025 μg/kg) was given 50 min after beginning the GDN infusion and compared with plasma concentrations following a similar GTN dose in the absence of dosed GDNs. No significant differences in GTN AUC (p0.9) and CLapp (p 0.7) were found. In a second set of experiments, an infusion of nitroglycerin was begun in each of 4 dogs and continued for 160 min at an infusion rate of 100 gm/min. Steady state concentrations of GTN were achieved within 100 min, at which time the dog received, simultaneously, an iv bolus dose (5.14 mg) of one of the GDNs and an infusion dose (100 gmg/min) of the same GDN. For both dinitrate metabolites no significant differences (p 0.5) were found between control and interaction arterial and venous clearances, although venous GTN clearances tended to decrease in the presence of dosed GDNs. Steady state systolic blood pressure during GDN infusions could be further reduced when GTN doses were administered; however, the steady state systolic blood pressure decrease caused by GTN could not be further reduced by the GDN infusions. Results suggest that the GDNs do not inhibit nitroglycerin metabolism or hemodynamics at the dose levels studied here.
    Type of Medium: Electronic Resource
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