Beta1-adrenoceptor-mediated relaxation with isoprenaline and the role of MaxiK channels in guinea-pig esophageal smooth muscle

• Published in: Journal of smooth muscle research Vol. 40; no. 2; pp. 43 - 52
• Main Authors: Tanaka, Yoshio, Shinoda, Keiko, Sekiya, Sarasa, Yamaki, Fumiko, Shibano, Mari, Yamashita, Yoko, Horinouchi, Takahiro, Koike, Katsuo
• Format: Journal Article
• Language: English
• Published: Japan 01.04.2004
• Subjects: Adrenergic beta-Agonists - pharmacology; Animals; Esophagus - drug effects; Esophagus - physiology; Female; Guinea Pigs; Isoproterenol - pharmacology; Large-Conductance Calcium-Activated Potassium Channels; Male; Muscle Relaxation - drug effects; Muscle, Smooth - drug effects; Muscle, Smooth - physiology; Peptides - pharmacology; Potassium Channel Blockers - pharmacology; Potassium Channels - physiology; Potassium Channels, Calcium-Activated - physiology; Potassium Chloride - pharmacology; Receptors, Adrenergic, beta-1 - physiology
• ISSN: 0916-8737; 1884-8796
• DOI: 10.1540/jsmr.40.43

The possible functional coupling between beta1-adrenoceptor and MaxiK channels which results in smooth muscle relaxation was examined in the guinea-pig esophageal muscularis mucosae. Isoprenaline-elicited relaxation of esophageal smooth muscle was confirmed to be mediated through beta1-adrenoceptors as the response was competitively antagonized by a beta1-selective antagonist atenolol with a pA2 value of 7.01. Iberiotoxin (IbTx, 10(-7) M), a selective MaxiK channel inhibitor, substantially diminished the relaxant response to isoprenaline. The extent of the MaxiK channel contribution to the relaxant response was 15-40% of the control response when estimated as the E50%-Emax responses to isoprenaline. The relaxation to isoprenaline was also attenuated by high-KCl (80 mM) to the same degree as the relaxant response generated in the presence of IbTx, and thus the estimated extent of the K+ channel contribution was 10-40%. These findings indicate that beta1-adrenoceptors are substantially coupled with MaxiK channels to produce relaxation of esophageal smooth muscle in the guinea-pig. Although MaxiK channels account for the contribution of K+ channels to the beta1-adrenoceptor-mediated relaxation in this smooth muscle preparation, their contribution seems to be less when compared to the beta2-adrenoceptor-mediated relaxation of tracheal smooth muscle.