Abstract 18673: Gαi2- Mediated Protection from Ischemic Injury is Modulated by Regulator of G Protein Signaling Proteins
Background: Agonists that act at Gαi-coupled receptors protect the heart from ischemic injury. The activity of Gαi is modulated by regulator of G protein signaling (RGS) proteins that terminate Gαi signaling by catalyzing the hydrolysis of Gαi-bound GTP. Gαi2 is the primary Gαi isoform in the myocardium. We used knock-in mice in which interactions between Gαi2 and RGS proteins are disrupted by a Gαi2G184S (GS) point mutation to determine whether interactions between Gαi2 and endogenous RGS proteins modulate Gαi-mediated protection from ischemic injury. We hypothesized that disruption of interactions between Gαi2 and RGS proteins would protect the heart from ischemic injury.
Methods: Hearts isolated from wildtype (+/+) mice and mice homozygous (GS/GS) or heterozygous (GS/+) for Gαi2G184S were perfused by the Langendorff method using the following protocol: 55 min perfusion; 30 min ischemia; 120 min reperfusion. Contractile function was monitored by an intraventricular balloon, and infarct size was measured by triphenyltetrazolium chloride staining. Hearts were paced at 500 bpm. All data from +/+, GS/+, and GS/GS hearts were compared by one way ANOVA and Tukey posthoc analysis.
Results: Infarcts in GS/GS hearts (12 ± 2% of area at risk; n = 8; p < 0.001) and GS/+ hearts (23 ± 3.0 % of area at risk; n = 15; p < .01) were significantly smaller than those of +/+ hearts (37 ± 3 % of AAR; n = 16). Expression of Gαi2G184S had no effect on preischemic contractile function. However, postischemic recovery of developed pressure (+/+: 36 ± 4 % GS/+: 50 ± 4 % GS/GS: 62 ± 2 % of preischemic value), +dP/dT (+/+:33 ± 5% GS/+: 50 ± 4 % GS/GS: 67 ± 3 % of preischemic value), and -dP/dT (+/+: 30 ± 4 % GS/+: 44 ± 4 % GS/GS: 59 ± 3 % of preischemic value) was significantly enhanced in GS/GS (p < .001) and GS/+ (p < .05) hearts compared to +/+ hearts (n = 8–16). Perfusion of 200 μM 5-hydroxydecanoic acid (5-HD) for 30 min prior to ischemia and for the first 15 min of reperfusion reversed the cardioprotective phenotype of GS/GS and GS/+ hearts.
Conclusion: Inhibition of interactions between endogenous RGS proteins and Gαi2 protects the heart from ischemic injury through a mechanism that involves 5-HD sensitive K+ channels. RGS proteins may provide a novel therapeutic target to protect the heart from ischemic injury.
- © 2010 by American Heart Association, Inc.