Ise Shinji, Nishimura Junji, Hirano Katsuya, Hara Nobuyuki, Kanaide Hideo
Department of Molecular Cardiology, Research Institute of Angiocardiology, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
Br J Pharmacol. 2003 Nov;140(5):939-47. doi: 10.1038/sj.bjp.0705508. Epub 2003 Sep 29.
Theophylline, a nonselective phosphodiesterase inhibitor, has long been regarded as a major bronchodilator in the treatment of human asthma. Using front-surface fluorometry with fura-2 and alpha-toxin permeabilization, the effects of theophylline on intracellular Ca2+ concentration ([Ca2+]i), tension development and Ca2+ sensitivity of the contractile apparatus were investigated in porcine tracheal smooth muscle strips. Application of theophylline induced a relaxation without a significant decrease in [Ca2+]i when strips were precontracted by 40 mm K+ depolarization, while theophylline significantly decreased both [Ca2+]i and tension induced by carbachol. The effects of theophylline on the increases in [Ca2+]i and tension induced by carbachol were significantly inhibited by iberiotoxin, an inhibitor of large-conductance Ca2+-activated K+ channels. In the absence of extracellular Ca2+, theophylline significantly attenuated carbachol-induced transient increases in tension development, while it did not affect carbachol-induced transient increase in [Ca2+]i. The [Ca2+]i-force relationship, which was determined by cumulative applications of extracellular Ca2+ (0-5 mm) during 40 mm K+ depolarization, was significantly shifted to the right by theophylline. In alpha-toxin permeabilized strips, theophylline significantly increased the EC50 value of [Ca2+]i for contraction and enhanced the effect of cAMP, but not of cGMP. These results indicate that theophylline induces relaxation of the porcine tracheal smooth muscle through an activation of BK channels, and a resultant decrease in [Ca2+]i and an attenuation of Ca2+ sensitivity, presumably through the action of cAMP.
氨茶碱，一种非选择性磷酸二酯酶抑制剂，长期以来一直被视为治疗人类哮喘的主要支气管扩张剂。使用fura-2前表面荧光测定法和α-毒素通透技术，研究了氨茶碱对猪气管平滑肌条细胞内Ca2+浓度（[Ca2+]i）、张力发展以及收缩装置Ca2+敏感性的影响。当条带通过40 mM K+去极化预收缩时，应用氨茶碱可诱导舒张，而[Ca2+]i无显著下降，而氨茶碱可显著降低卡巴胆碱诱导的[Ca2+]i和张力。氨茶碱对卡巴胆碱诱导的[Ca2+]i和张力增加的作用被大电导Ca2+激活K+通道抑制剂iberiotoxin显著抑制。在无细胞外Ca2+的情况下，氨茶碱显著减弱卡巴胆碱诱导的张力发展的瞬时增加，而不影响卡巴胆碱诱导的[Ca2+]i瞬时增加。在40 mM K+去极化期间通过累积应用细胞外Ca2+（0 - 5 mM）测定的[Ca2+]i-力关系被氨茶碱显著向右移动。在α-毒素通透的条带中，氨茶碱显著增加收缩的[Ca2+]i的EC50值，并增强cAMP的作用，但不增强cGMP的作用。这些结果表明，氨茶碱通过激活BK通道诱导猪气管平滑肌舒张，导致[Ca2+]i降低和Ca2+敏感性减弱，推测是通过cAMP的作用实现的。
