Allergic responses reduce the relaxant effect of beta-agonists but not potassium channel openers in guinea-pig isolated trachea

Abstract

This study was conducted to determine whether the relaxant effect of adenosine triphosphate (ATP)-sensitive potassium channel (KATP) openers on airway smooth muscle are reduced during the hyporesponsiveness of beta-adrenergic receptors. Isometric tension was measured and dose-response curves were constructed for levcromakalim (a KATP opener), Y-26763 (another KATP opener), isoprenaline and theophylline in guinea-pig isolated trachea that was challenged with ovalbumin or pretreated in vitro with either isoprenaline or the KATP openers. Antigen challenge in vitro significantly reduced the potency but not the efficacy of isoprenaline in tracheal strips from actively sensitized guinea-pigs. The concentration of drug that produced a half-maximum inhibition (IC50) was 0.014 +/- 0.004 microM in the challenge group versus 0.006 +/- 0.001 microM in the control group (p < 0.05; n = 9). The IC50 of levcromakalim (1.73 +/- 0.17 microM; n = 6) and of theophylline (110 +/- 3.1 microM; n = 6) were unaffected. Exposure to 4 microM isoprenaline for 30 min evoked beta-adrenergic hyporesponsiveness: the IC50 of isoprenaline rose significantly from 0.010 +/- 0.001 to 0.017 +/- 0.002 microM (p < 0.01; n = 6). No effect was observed on the relaxant actions of levcromakalim and theophylline. In contrast, prior incubation with either levcromakalim or Y-26763 (300 microM for 30 min) significantly reduced the subsequent potency and efficacy of levcromakalim, but did not alter the effects of isoprenaline and theophylline. We conclude that the relaxant effect of the adenosine triphosphate-sensitive potassium channel openers was independent of beta-adrenergic hyporesponsiveness in airway smooth muscle of guinea-pigs.

High throughput measurement of Ca2+ dynamics for drug risk assessment in human stem cell-derived cardiomyocytes by kinetic image cytometry

“…1c) cannot fully describe chaotic behaviors, they nonetheless were in general agreement with EC 50 or IC 50 values described in the literature. Specifically, the KIC values were in agreement with the values reported for the L-type Ca 2+ channel blocker verapamil (Zahradnik, et al, 2008; Zhang, et al, 1999), the L-type Ca 2+ channel activator Bay K 8644 (Ogawa, et al, 1992), the K ATP channel opener levcromakalim (Houjou, Iizuka, Dobashi, & Nakazawa, 1996), the hERG K + channel activator NS1463 (Hansen, et al, 2006) and the hERG blockers cisapride (Mohammad, et al, 1997; Potet, Bouyssou, Escande, & Baró, 2001; Toga, et al, 2007) and E-4031 (Fossa, et al, 2004). We identified a lower than reported EC 50 for the hERG blocker dofetilide (Snyders & Chaudhary, 1996), and sotalol (Peng, Lacerda, Kirsch, Brown, & Bruening-Wright) as well as for the Na + channel blocker flecainide (Ramos & O'Leary, 2004).…”