An antagonistic 5-HT receptor system in the auricles of the systemic heart complex of Sepia officinalis L. (Cephalopoda) shows 5-HT1 and 5-HT4 subtype properties |
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Authors: | Lehr Tobias Schipp Rudolf |
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Affiliation: | Institut für Allgemeine und Spezielle Zoologie, Abteilung Entwicklungsbiologie, Stephanstrasse 24, D-35390 Giessen, Germany. |
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Abstract: | In pharmacological bioassays on isolated ring-shaped auricle preparations of Sepia officinalis, the action of the specific 5-hydroxytryptamine (5-HT) agonists 8-OH-DPAT (5-HT1a), CP-93129 (5-HT1b), TFMPP (5-HT1b) and RS-67333 (5-HT4) on these autonomously contractile compartments was studied. 8-OH-DPAT and CP-93129 induced mainly positive effects on frequency and tone on the isotonically suspended auricles. The positive effect of 8-OH-DPAT on frequency was blocked by the specific 5-HT1a antagonist NAN-190. The 5-HT1b agonist TFMPP caused similar effects on tone and a positive impact on the auricular amplitude. The highly specific 5-HT4 agonist RS-67333 induced an effect opposite to the action of 5-HT1 agonists inducing mainly negative effects on frequency, amplitude and tone, causing a diastolic standstill at a concentration of 10(-6) M. These negative effects were blocked by the adenylyl cyclase inhibitor SQ-22,536 in the absence of a diastolic standstill. The opposing action of 5-HT1 and 5-HT4 agonists on auricular contractile activity suggests that an antagonistic 5-HT-receptor system exists within the auricular myocardial cells of S. officinalis, probably consisting of 5-HT1- and 5-HT4-like subtypes. The results also suggest that adenylyl cyclase acts as the intracellular target enzyme of both signal transduction mechanisms. |
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Keywords: | 5-HT 5-hydroxytryptamine (=serotonin) 8-OH 8-OH-DPAT cN centi Newton CP CP-93129 maximum excitatory concentration half-maximum excitatory concentration h hour(s) min minute NAN NAN-190 RS RS-67333 S.E.M. standard error of the mean SQ SQ-22,536 (adenylyl cyclase inhibitor) SW sea water v/v volume/volume Invertebrate Adenylyl cyclase cAMP Cephalopod Mollusc 5-HT receptor Pharmacological bioassay |
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