Meeting Abstract
P3.4 Tuesday, Jan. 6 FMRFamide and 5HT Increase IP3 levels in gastropod hearts DEATON, L. E.; Univ. of Louisiana at Lafayette led9784@louisiana.edu
The hearts of molluscs are myogenic, but the cardiac output is modulated by a variety of classical neurotransmitters and endogenous neuropeptides. Both 5-hydroxytryptamine (5HT) and the molluscan neuropeptide FMRFamide are cardioexcitatory in gastropod molluscs. However, the mechanisms involved in the effects of these agents on the ventricle are poorly understood. To clarify the possible roles of cellular signaling pathways in the excitatory effects of FMRFamide and 5HT on the hearts of molluscs, ventricles were isolated from the marine snail Melongena corona and exposed to seawater (SW) or to SW containing either 5HT or FMRFamide for 10 sec. The tissues were then homogenized and assayed for cAMP and IP3 with commercial kits. The cAMP content of controls was 0.38 pmol/mg wet wt. The cAMP level in 5HT (10-6 M) and FMRFamide (10-6 M)-treated tissues was, respectively, 0.42 and 0.47 pmol/mg. Ventricles treated with forskolin (10-5 M) had a cAMP level of 0.31 pmol/mg. Control ventricles contained 0.13 pmol/mg IP3. The level of IP3 was 0.32 pmol/mg in 5HT-treated tissues and 0.55 pmol/mg in FMRFamide-treated hearts. In addition, phorbol esters caused positive inotropy similar to the effects of 5HT and FMRFamide in isolated hearts. Neither forskolin nor cholera toxin had any effect on the mechanical activity of isolated hearts. These results suggest that the excitation of gastropod hearts by 5HT and FMRFamide involves the activation of the phosphoinositol phosphate cellular signaling pathway, but not the cAMP second messenger pathway.
