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Ca 2+ responses to thyrotropin‐releasing hormone and angiotensin II: the role of plasma membrane integrity and effect of G 11 α protein overexpression on homologous and heterologous desensitization
Author(s) -
Ostasov Pavel,
Krusek Jan,
Durchankova Dana,
Svoboda Petr,
Novotny Jiri
Publication year - 2008
Publication title -
cell biochemistry and function
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.933
H-Index - 61
eISSN - 1099-0844
pISSN - 0263-6484
DOI - 10.1002/cbf.1453
Subject(s) - receptor , homologous desensitization , medicine , endocrinology , desensitization (medicine) , angiotensin ii , stimulation , g protein coupled receptor , signal transduction , thyrotropin releasing hormone , hormone , g protein , chemistry , biology , microbiology and biotechnology
The molecular mechanisms involved in GPCR‐initiated signaling cascades where the two receptors share the same signaling cascade, such as thyrotropin‐releasing hormone (TRH) and angiotensin II (ANG II), are still far from being understood. Here, we analyzed hormone‐induced Ca 2+ responses and the process of desensitization in HEK‐293 cells, which express endogenous ANG II receptors. These cells were transfected to express exogenously high levels of TRH receptors (clone E2) or both TRH receptors and G 11 α protein (clone E2M11). We observed that the characteristics of the Ca 2+ response, as well as the process of desensitization, were both strongly dependent on receptor number and G 11 α protein level. Whereas treatment of E2 cells with TRH or ANG II led to significant desensitization of the Ca 2+ response to subsequent addition of either hormone, the response was not desensitized in E2M11 cells expressing high levels of G 11 α . In addition, stimulation of both cell lines with THR elicited a clear heterologous desensitization to subsequent stimulation with ANG II. On the other hand, ANG II did not affect a subsequent response to TRH. ANG II‐mediated signal transduction was strongly dependent on plasma membrane integrity modified by cholesterol depletion, but signaling through TRH receptors was altered only slightly under these conditions. It may be concluded that the level of expression of G‐protein‐coupled receptors and their cognate G‐proteins strongly influences not only the magnitude of the Ca 2+ response but also the process of desensitization and resistance to subsequent hormone addition. Copyright © 2007 John Wiley & Sons, Ltd.