MCPHERSON, Duane; SZALKOWSKI, Veronica; SUNY at Geneseo; SUNY at Geneseo: Serotonin receptor-specific agonists and cyclic AMP accumulation in Aplysia foot muscle

In foot muscle of the marine mollusc Aplysia californica, serotonin (5-HT) increases the force of motoneuron-evoked contractions and also increases muscle relaxation rate. In isolated foot muscle, the same concentration of 5-HT (10 micromolar, bath-applied) causes a large increase in cAMP content, about 200-fold on average. We are attempting to characterize the muscle 5-HT receptor pharmacologically and have tested four 5-HT agonists, namely, &alpha-methyl-5-HT, 8-hydroxy-DPAT, 5-carboxamidotryptamine (5-CT) and 2-methyl-5-HT. Bath-applied at 10 to 1000 micromolar, the first three did increase cAMP content but even at the highest doses none of them increased cAMP content as much as 5-HT did at 10 micromolar. Application of &alpha-methyl-5-HT at 1000 micromolar caused the largest increase in [cAMP] among the agonists, followed by 5-CT and 8-hydroxy DPAT, while 2-methyl-5-HT did not increase [cAMP] at any dose. These results are discussed in comparison to the pharmacological profiles of other invertebrate and vertebrate serotonin receptors.