5-hydroxytryptamine regulates the (Na++K+)ATPase activity in malpighian tubules of Rhodnius prolixus: Evidence for involvement of G-protein and cAMP-dependent protein kinase
✍ Scribed by Maria Angela B. Grieco; Aníbal Gil Lopes
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 143 KB
- Volume
- 36
- Category
- Article
- ISSN
- 0739-4462
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✦ Synopsis
5-Hydroxytryptamine (5-HT, serotonin) acts as a diuretic hormone in Rhodnius prolixus, where it increases to 0.1 µM in the haemolymph during feeding and stimulates the fluid secretion in isolated Malpighian tubules. The ouabain-sensitive (Na + +K + )ATPase activity present in homogenates of Malpighian tubules from unfed Rhodnius prolixus is inhibited 60% by 0.01 µM 5-HT. This inhibition is reversed by ketanserin, a 5-HT 2 receptor antagonist in mammals, and also by GDPβS, a competitive inhibitor of G-protein GTPase activity. GTPγS, a nonhydrolysable analog of GTP, and cholera toxin, a G s -protein activator, also inhibit the ouabainsensitive (Na + +K + )ATPase activity, while pertussis toxin, a G i -protein inhibitor, has no effect. The (Na + +K + )ATPase activity is inhibited 55% by 0.4-100 µM dibutyryl-cAMP in the presence of IBMX, a phosphodiesterase inhibitor, which also potentiates the effect of a low concentration of 5-HT. The cAMP-dependent protein kinase inhibitor peptide abolishes the 5-HT effect. These data suggest that the (Na + +K + )ATPase activity in Malpighian tubules is inhibited by 5-HT through activation of G s -protein and a cAMP-dependent protein kinase. Inhibition of the Na + +K + pump would contribute to the diuretic effect of 5-HT. Arch.