Effects of azelastine on contraction of guinea pig tracheal smooth muscle.
Azelastine [4-(p-chlorobenzyl)-2-(hexahydro-1-methyl-1H-azepine-4-yl)-1(2H)-phthalazinone hydrochloride] is a new anti-asthmatic drug. We examined the mechanism of its inhibitory action on guinea pig tracheal smooth muscle contraction by measuring membrane potential and isometric force using intracellular microelectrodes and a micro-force transducer. The mean resting membrane potential of guinea pig tracheal muscle cells was -54 mV. Perfusion with 20 mM tetraethylammonium (TEA) caused membrane depolarization and elicited spontaneous action potentials. Azelastine (1-100 microM) suppressed both the amplitude and maximal rate of rise of the action potentials in a concentration-dependent manner. Complete abolition occurred at 100 microM. Similarly, azelastine (0.1-100 microM) inhibited and abolished 50 mM KCl-induced contractions. These results suggest that azelastine may inhibit voltage-dependent Ca2+ channels. Next, pretreatment of tracheal muscle (for 15 min) with azelastine (0.01-100 microM) inhibited subsequent acetylcholine (ACh) (0.01-100 microM)-induced contractions. Azelastine, 100 microM, completely abolished the ACh-induced contractions. In contrast, high concentrations of Ca2+ channel antagonists diltiazem (10-100 microM) or nifedipine (20 microM), and Ca2(+)-free solution, only partially depressed the ACh contractions suggesting that azelastine has an additional effect on intracellular Ca2+ release. In Ca2(+)-free solution (containing 0.5 mM EGTA), azelastine (1-100 microM) depressed and abolished the transient contractions induced by 10 microM ACh. We conclude that azelastine inhibits airway constriction by inhibiting both voltage-sensitive Ca2+ slow channels on the cell membrane and Ca2+ release from a intracellular storage site.
Lee
H K
HK
Department of Physiology and Biophysics, University of Cincinnati College of Medicine, OH 45267.
Ohya
Y
Y
Doupnik
C A
CA
Sperelakis
N
N
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001993:Bronchodilator Agents / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008839:Microelectrodes; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D010793:Phthalazines / Q000494:pharmacology*; D011189:Potassium Chloride / Q000494:pharmacology; D014132:Trachea / Q000187:drug effects
D001993:Bronchodilator Agents; D010793:Phthalazines; D011189:Potassium Chloride; C020976:azelastine