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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
Author(s) -
Grieco Maria Angela B.,
Lopes Aníbal Gil
Publication year - 1997
Publication title -
archives of insect biochemistry and physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.576
H-Index - 66
eISSN - 1520-6327
pISSN - 0739-4462
DOI - 10.1002/(sici)1520-6327(1997)36:3<203::aid-arch4>3.0.co;2-u
Subject(s) - rhodnius prolixus , malpighian tubule system , ouabain , biology , protein kinase a , ibmx , endocrinology , medicine , pertussis toxin , g protein , biochemistry , receptor , forskolin , kinase , chemistry , midgut , sodium , insect , ecology , botany , organic chemistry , larva
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 ouabain‐sensitive (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. Insect Biochem. Physiol. 36:203–214, 1997. © 1997 Wiley‐ Liss, Inc.