Zoological Studies

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

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.