Abstract
Modulation of the spontaneous myogenic contraction of the lateral oviduct by biogenic monoamines octopamine and serotonin was studied in the cricket Gryllus bimaculatus. Octopamine and serotonin caused an increase and a decrease in the frequency of myogenic contraction, respectively. Application of the octopamine receptor antagonist phentolamine and the serotonin receptor antagonist ketanserin attenuated the effects of octopamine and serotonin, respectively. The excitatory action of octopamine could be mimicked by application of 8-bromo-cAMP, a membrane-permeable cAMP analog. GsMTx-4, a peptide toxin that possesses specific blocking activity for the stretch-activated (SA) channel decreased the frequency of myogenic contraction. In order to determine whether SA channel is involved in the modulation of myogenic contraction, single SA channel currents were recorded from the cell-attached membrane patches in myocytes isolated from the cricket lateral oviduct. Application of octopamine and serotonin on myocytes increased and decreased the open probability (Po) of the SA channels, respectively. Phentolamine and ketanserin reduced the octopamine- and serotonin-induced effect, respectively. An increase in Po was also observed by bath application of 8-bromo-cAMP. These results indicate that SA channel is involved in the modulation of the myogenic contraction by octopamine and serotonin and that cAMP signaling pathway is involved in the excitatory action of octopamine. [J Physiol Sci. 2008;58 Suppl:S84]
