ABSTRACT
Potentiation of hormone actions can occur by different mechanisms, including inhibition of degrading enzymes, interaction with the hormone receptor leading to stabilization of bioactive conformation or leading to receptor homo- and hetero-oligomerization, receptor phosphorylation and dephosphorylation or can occur by directly influencing the signal transduction and ion channels. In this review the potentiation of bradykinin actions in different systems by certain compounds will be reviewed. Despite many long years of experimental research and investigation the mechanisms of potentiating action remain not fully understood. One of the most contradictory findings are the distinct differences between the inhibition of the angiotensin I-converting enzyme and the potentiation of the bradykinin induced smooth muscle reaction. Contradictory findings and hypothesized mechanisms in the literature are discussed in this review and in some cases compared to own results. Investigation of potentiating actions was extended from hypotension, smooth muscle reaction and cellular actions to activation of immunocompetent cells. In our opinion the potentiation of bradykinin action can occur by different mechanisms, depending on the system and the applied potentiating factor used.
ABSTRACT
Synthetic analogues of the bradykinin potentiating nonapeptide BPP9alpha indicate significantly different structural requirements for potentiation of the bradykinin (BK)-induced smooth muscle contraction (GPI) and the inhibition of isolated somatic angiotensin I-converting enzyme (ACE). The results disprove the ACE inhibition as the only single mechanism and also the direct interaction of potentiating peptides with the bradykinin receptors in transfected COS-7 cells as molecular mechanism of potentiation. Our results indicate a stimulation of inositol phosphates (IPn) formation independently from the B2 receptor. Furthermore, the results with La3+ support the role of extracellular Ca2+ and its influx through corresponding channels. The missing effect of calyculin on the GPI disproves the role of phosphatases in the potentiating action. These experimental studies should not only contribute to a better understanding of the potentiating mechanisms but also incorporate a shift in the research towards the immune system, in particular towards the immunocompetent polymorphonuclear leukocytes. The chemotaxis of these cells can be potentiated most likely by exclusive inhibition of the enzymatic degradation of bradykinin. Thus the obtained results give evidence that the potentiation of the bradykinin action can occur by different mechanisms, depending on the system and on the applied potentiating factor.
Subject(s)
Angiotensin-Converting Enzyme Inhibitors/pharmacology , Bradykinin/pharmacology , Muscle Contraction/drug effects , Teprotide/analogs & derivatives , Amino Acid Sequence , Angiotensin-Converting Enzyme Inhibitors/chemical synthesis , Angiotensin-Converting Enzyme Inhibitors/chemistry , Animals , COS Cells , Calcium/metabolism , Chlorocebus aethiops , Drug Synergism , Guinea Pigs , Humans , Inositol Phosphates/biosynthesis , Molecular Sequence Data , Muscle, Smooth/drug effects , Peptides/chemical synthesis , Peptides/chemistry , Peptides/pharmacology , Peptidyl-Dipeptidase A/drug effects , Phosphoprotein Phosphatases/antagonists & inhibitors , Receptor, Bradykinin B2/agonists , Receptor, Bradykinin B2/genetics , Signal Transduction/drug effects , Teprotide/chemistryABSTRACT
To study the intramolecular signal transduction, we performed single point and cassette mutations in transmembranal and intracellular regions of the bradykinin B2 receptor. We studied the influence of the two intramembranal Cys residues at positions 304 and 348, the role of Arg at position 177 in the highly conserved tripeptide sequence Asp-Arg-Tyr, the cytosolic G-protein binding area, and attempted to verify the general hypothesis of an ion tunnel-like interface in GPCRs. Wild type receptor, His-tagged receptor, and His-tagged mutant receptors were expressed in COS-7 cells and functionally compared by bradykinin-induced formation of inositolphosphate and arachidonic acid. To investigate the expression, all mutants were modified at the N-terminus by insertion of two successive His-tags and detected with an anti-poly-His antibody. Replacement of the second and third cytosolic loop by a loop from another membrane protein as well as single replacement of Arg at position 177 by Ala leads to a fully inactive receptor mutant without any ligand binding affinity and stimulatory activity. Mutants with replacement of Cys residues 304 and 348 by Ser showed only moderate effects. Regardless of the replacement of Asp 407 by Ala, the receptor is able to increase the agonist-induced levels of inositolphosphate and of arachidonic acid, indicating that our studies can not verify the postulated ion tunnel hypothesis.
