Gi Proteins Regulate Adenylyl Cyclase Activity Independent of Receptor Activation
| Autor: | Øivind Ørstavik, Tor Skomedal, Kurt A. Krobert, Finn Olav Levy, Caroline Bull Melsom, Jan-Bjørn Osnes |
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| Jazyk: | angličtina |
| Rok vydání: | 2014 |
| Předmět: |
Male
Cell signaling lcsh:Medicine Signal transduction GTP-Binding Protein alpha Subunits Gi-Go Phosphodiesterase 3 Inhibitors Bioinformatics Signaling Molecules Adenylyl cyclase chemistry.chemical_compound Medicine and Health Sciences Cyclic AMP Myocytes Cardiac lcsh:Science Multidisciplinary ADCY9 Signaling cascades Stereoisomerism cAMP signaling cascade Cell biology ADP-ribosylation population characteristics geographic locations Research Article Adenylyl Cyclases Signal Inhibition G protein Adenylyl Cyclase Signaling Pathway Cardiology Pertussis toxin Cardiovascular Pharmacology ADCY10 parasitic diseases Animals Rats Wistar Adenylyl cyclase signaling cascade Fenoterol G protein-coupled receptor Biology and life sciences lcsh:R social sciences Cyclic Nucleotide Phosphodiesterases Type 4 Rats Enzyme Activation Pertussis Toxin chemistry lcsh:Q Phosphodiesterase 4 Inhibitors human activities Adrenergic Signal Transduction |
| Zdroj: | PLoS ONE, Vol 9, Iss 9, p e106608 (2014) PLoS ONE |
| ISSN: | 1549-1277 |
| Popis: | BACKGROUND AND PURPOSE: Despite the view that only β2- as opposed to β1-adrenoceptors (βARs) couple to G(i), some data indicate that the β1AR-evoked inotropic response is also influenced by the inhibition of Gi. Therefore, we wanted to determine if Gi exerts tonic receptor-independent inhibition upon basal adenylyl cyclase (AC) activity in cardiomyocytes. EXPERIMENTAL APPROACH: We used the Gs-selective (R,R)- and the Gs- and G(i)-activating (R,S)-fenoterol to selectively activate β2ARs (β1AR blockade present) in combination with Gi inactivation with pertussis toxin (PTX). We also determined the effect of PTX upon basal and forskolin-mediated responses. Contractility was measured ex vivo in left ventricular strips and cAMP accumulation was measured in isolated ventricular cardiomyocytes from adult Wistar rats. KEY RESULTS: PTX amplified both the (R,R)- and (R,S)-fenoterol-evoked maximal inotropic response and concentration-dependent increases in cAMP accumulation. The EC50 values of fenoterol matched published binding affinities. The PTX enhancement of the Gs-selective (R,R)-fenoterol-mediated responses suggests that Gi regulates AC activity independent of receptor coupling to Gi protein. Consistent with this hypothesis, forskolin-evoked cAMP accumulation was increased and inotropic responses to forskolin were potentiated by PTX treatment. In non-PTX-treated tissue, phosphodiesterase (PDE) 3 and 4 inhibition or removal of either constitutive muscarinic receptor activation of Gi with atropine or removal of constitutive adenosine receptor activation with CGS 15943 had no effect upon contractility. However, in PTX-treated tissue, PDE3 and 4 inhibition alone increased basal levels of cAMP and accordingly evoked a large inotropic response. CONCLUSIONS AND IMPLICATIONS: Together, these data indicate that Gi exerts intrinsic receptor-independent inhibitory activity upon AC. We propose that PTX treatment shifts the balance of intrinsic G(i) and Gs activity upon AC towards Gs, enhancing the effect of all cAMP-mediated inotropic agents. |
| Databáze: | OpenAIRE |
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