FMRFamide-activated signal transduction pathways in the crop-gizzard of the earthworm, Lumbricus terrestris

Author

Jamey Krauss

Graduation Date

2007

Document Type

Thesis

Program

Other

Program

Thesis (M.A.)--Humboldt State University, Biology, 2007

Committee Chair Name

Bruce A. O'Gara

Committee Chair Affiliation

HSU Faculty or Staff

Keywords

Humboldt State University -- Theses -- Biology, Earthworms, FMRFamide, Signal transduction pathways, Lumbricus terrestris, Crop-gizzard

Abstract

In this study, I examined the effects of FMRFamide on the isolated crop-gizzard of the earthworm, Lumbricus terrestris. The peptide induced contractions of both the longitudinal and circular muscles of the crop-gizzard at concentrations examined (10-9 to 10-5 M). The responses were quantified by measuring increases in basal tonus, peak tension, integrated area, mean contraction amplitude, and contraction rate. FMRFamide application induced concentration-dependent decreases in basal tonus increase, peak tension, integrated area, and mean contraction amplitude of the longitudinal muscles. However, FMRFamide application induced a biphasic response in contraction rate where at low concentrations (10-9 to 10-7 M) there was an increase in contraction rate, but at high concentrations (10-6 – 10-5 M) the rate decreased and approached control values. FMRFamide application induced a complex multiphasic effect in basal tonus increase, peak tension, and integrated area of the circular muscles. At low concentrations (10-9 – 10-8 M) there was a decrease in each FMRFamide-induced response, whereas at higher concentrations (10-7 – 10-6 M) the FMRFamide-induced responses increased before falling at the highest exposure (10-5 M). Additionally, FMRFamide induced a concentration-dependent biphasic effect on mean contraction amplitude, whereas the contraction rate revealed an excitatory trend as FMRFamide concentrations increased. The main aim of this study was to determine which signal transduction pathways were activated by FMRFamide in the crop-gizzard. It was discovered that the crop-gizzard lacks amiloride-sensitive sodium channels gated by FMRFamide. Second messenger pathway manipulation experiments suggested that the phosphatidylinositol and arachidonic acid pathways are involved in the FMRFamide-induced responses. FMRFamide-induced responses were reduced by the protein kinase C inhibitors, H-7 (5 ×10-5 M) and BIM I (10-5 M), calcium-calmodulin kinase II inhibitor, KN-62 (10-5 M), phospholipase A2 inhibitor, 4-BPB (10-6 M), and the phospholipase A2 and phospholipase C inhibitor, U-73122 (18 × 10-6 M). However, there was no evidence to suggest that the cAMP or NO-induced cGMP second messenger pathways were involved in the FMRFamide induced responses. FMRFamide-induced responses were unaffected by the protein kinase A inhibitor, H-89 (10-6 M), adenylyl cyclase inhibitor, MDL-12,330A (10-5 M), and guanylyl cyclase inhibitor, ODQ (10-6 M). Additionally, application of the cAMP analog, 8-Br-cAMP (10-5 M), NO donor, SNAP (10-5 M), and cGMP analog, 8-Br-cGMP (10-5 M) produced contractile responses that did not resemble those induced by FMRFamide. Certain drug treatments alone induced distinct contractile responses of the crop-gizzard, indicating the role of specific transduction mechanisms in mediating crop-gizzard spontaneous activity. Normal crop-gizzard spontaneous activity was altered by the calmodulin inhibitor, W-7 (10-4 M), and the tyrosine kinase inhibitor, genistein (5 × 10-5 M).

https://scholarworks.calstate.edu/concern/theses/6q182n61v

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