Table of Contents
ISRN Pharmacology
Volume 2013 (2013), Article ID 207671, 8 pages
http://dx.doi.org/10.1155/2013/207671
Research Article

An Inotropic Action Caused by Muscarinic Receptor Subtype 3 in Canine Cardiac Purkinje Fibers

1Department of Rational Medicinal Science, Faculty of Pharmaceutical Sciences, Doshisha Women’s College, Kyoto, Kyotanabe-shi 610-0395, Japan
2Department of Pathological Physiology, Faculty of Pharmaceutical Sciences, Doshisha Women’s College, Kyoto, Kyotanabe-shi 610-0395, Japan
3Department of Pharmacology, Hatano Research Institute, Food and Drug Safety Center, Kanagawa, Hadano-shi 257-8523, Japan

Received 5 July 2013; Accepted 28 August 2013

Academic Editors: K. Cimanga, R. Fantozzi, M. C. Olianas, and J. D. Salamone

Copyright © 2013 Katsuharu Tsuchida et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Objective. The objective of this study was to investigate the inotropic mechanisms and the related muscarinic receptor subtype of acetylcholine (ACh) in canine cardiac Purkinje fibers. Materials and Methods. Isolated Purkinje fiber bundles were used for the measurement of contraction. The receptor subtype was determined using PCR and real-time PCR methods. Results. ACh evoked a biphasic response with a transient negative inotropic effect followed by a positive inotropic effect in a concentration-dependent manner. The biphasic inotropic actions of ACh were inhibited by the pretreatment with atropine. Caffeine inhibited the positive inotropic effect of ACh. ACh increased inositol-1,4,5-trisphosphate content in the Purkinje fibers, which was abolished by atropine. Muscarinic subtypes 2 (M2) and 3 (M3) mRNAs were detected in the canine Purkinje fibers albeit the amount of M3 mRNA was smaller than M2 mRNA. M1 mRNA was not detected. Conclusion. These results suggest that the positive inotropic action of ACh may be mediated by the activation of IP3 receptors through the stimulation of M3 receptors in the canine cardiac Purkinje fibers.