© 2002 by European Society of Cardiology
Copyright © 2001, European Society of Cardiology
Endotoxin induces desensitization of cardiac endothelin-1 receptor signaling by increased expression of RGS4 and RGS16
aMedizinische Klinik, Abteilung für Kardiologie, Universitäts-Krankenhaus Hamburg Eppendorf, Martinistr. 52, 20246 Hamburg, FRG
bInstitut für Experimentelle und Klinische Pharmakologie und Toxikologie, Universitäts-Krankenhaus Hamburg Eppendorf, Martinistr. 52, 20246 Hamburg, FRG
* Corresponding author. Tel.: +49-40-42803-5989; fax: +49-40-42803-4884 patten{at}uke.uni-hamburg.de
Objective: Endotoxin (LPS)-induced acute cardiac failure during sepsis is associated with alterations in G protein mediated signal transduction. We therefore examined the expression of the G proteins Gi, Gq, and Gs and of four ‘regulators of G protein signaling’ (RGS) proteins, RGS1, RGS4, RGS5, and RGS16 in rat hearts. Methods: For in vivo experiments, Wistar rats were treated with 600 µg/day E. coli LPS, intravenously) and hearts were excised after 6, 24 and 72 h. Cultured neonatal rat cardiomyocytes were treated with 4 µg/ml LPS for 24 and 72 h. Isolated membrane proteins were used for Western blot analysis and for evaluation of phospholipase C (PLC) activity. RGS16 mRNA was detected by RNAse protection. Results: LPS induced Gi protein 1.4-fold 72 h after in vivo administration of LPS, whereas expression of Gs and Gq was unaltered. After 6 h of LPS treatment, RGS16 mRNA was transiently up-regulated 3.7-fold, followed by transient protein induction (24 h: 2.5-fold; 72 h: 1.5-fold). Similarly, RGS4 protein was transiently induced (24 h: 3.1-fold; 72 h: 1.5-fold), whereas expression of RGS1 and RGS5 was not altered. Similar to the LPS-treated rat hearts, RGS16 expression was transiently induced by LPS in cultured neonatal rat cardiomyocytes (24 h: 1.6-fold, 72 h: 0.9-fold). To determine the functional consequences of the RGS protein induction phospholipase C (PLC) activity was analyzed in membranes obtained from solvent and LPS-treated hearts. Basal and endothelin-1-stimulated PLC activity was transiently repressed by LPS with a maximum after 24 h although no apparent changes in PLCβ1 or endothelin receptor expression could be detected. Conclusion: These data suggest that the rapid up-regulation of cardiac RGS4 and RGS16 is associated with a desensitization of endothelin-1 receptor signaling. Up-regulation of these RGS proteins may thus be involved in the early onset of cardiac failure during sepsis.
KEYWORDS Endotoxins; Heart failure; G-Proteins; Sepsis; Signal transduction