Zoological Studies

Vol. 44 No. 4, 2005

5-HT 2 and 3 Agonists Influence the Contraction Activity of the Auricles from the Central Heart Complex of Sepia officinalis L. (Cephalopoda)

Tobias Lehr1,2 and Rudolf Schipp1,2,*

1Institut für Allgemeine und Spezielle Zoologie, Bereich Entwicklungsbiologie, Stephanstrasse 24, D-35390 Giessen, Germany
2Laboratoire d,Oceanographie Biologique, F-33120 Arcachon, France

Tobias Lehr and Rudolf Schipp (2005) In this study we investigated the effects of specific 5-HT2 and 5-HT3 agonists on the contraction activity of isolated auricles from the cuttlefish Sepia officinalis. We show that the specific 5-HT2 agonists, m-CPP and α-CH3-5- HT, increased the contraction force of the auricles and that the effect of α-CH3-5-HT was blocked by the selective 5-HT2 antagonist ketanserin, the membrane-permeable phospholipase C inhibitor U-73122 and the membrane-permeable D-myo-inositol 1,4,5-trisphosphate (IP3) receptor antagonist 2-aminoethoxy-diphenylborane (2-APB). These results suggest that a subtype of the 5-HT2-like receptor seems to be involved in regulation of the contraction force of the auricle. The blocking effect of the membrane-permeable enzyme inhibitors of the 5- HT2-specific signal transduction enzymes confirms that the cell response is triggered by the phosphatidylinositol-response including phospholipase C activation and the IP3-dependent signal transduction pathway in the auricular myocardium. In addition, we show that the specific 5-HT3-agonists 1-phenylbiguanide (1-PBG), mchlorophenylbiguanide (m-CPBG) and 2-CH3-5-HT evoked concentration-dependent excitatory effects on the isolated auricles. While all tested 5-HT3 agonists increased the frequency of the auricles, only 2-CH3-5HT increased the contraction force of the auricles, and only 1-PBG caused positive effects on the tone of the isolated auricles. These results suggest that except for a 5-HT2-like receptor, signal transduction mechanisms sensitive to 5-HT3 agonists, and possibly an ion channel receptor are involved in the neuroregulation, primarily modulation of the heart frequency, of S. officinalis auricles.

Key words: Mollusca, PI-response, Ion channel, PLC, Sepia.

*Correspondence: Tel: 49-641-9935602. Fax: 49-641-9935609. E-mail: Rudolf.Schipp@allzool.bio.uni-giessen.de