Abstract 227: Phosphorylation Patterning Determined by AMP-Activated Kinase, the LKB1/MO25/STRAD Complex, and Protein Phosphatase 1 Alters Contractile Function in Cardiac Rat Trabeculae
Post-translational modifications (PTM) of myofilament proteins alter contractile function of the heart in healthy as well as diseased myocardium and the patterning of PTMs can influence cardiac disease progression. PTM of the thin filament regulatory protein cardiac troponin I (cTnI) is known to modify contractile properties, including steady-state Ca2+ sensitivity of force and crossbridge cycling rates. Accordingly, the purpose of this study was to determine the effect of cTnI PTM patterning on myofilament function. Therefore, I hypothesize that the impact of cTnI PTM on contractile function will depend on the relative phosphorylation levels. To do this, demembranated rat cardiac trabeculae from 2 month-old male Sprague-Dawley rats were treated with AMP activated kinase (AMPK) (0.005 U/ µL), Protein Phosphatase 1 (PP1) (1U/µL), and the upstream AMPK kinase, the LKB1/MO25/STRAD complex (0.2 mU/µL). Fibers that were incubated with activated AMPK displayed an increase in Ca2+ sensitivity compared to untreated control fibers (EC50 1.41±0.08 μM [n=2] vs. 2.52±0.43 μM [n=9] p<0.001). PP1 treatment, previously shown to decrease cTnI phosphorylation, tended to increase Ca2+ sensitivity compared to untreated fibers (EC50 2.31 μM [n=1] vs. 2.52±0.43 μM [n=9]). Interestingly, PP1 treatment also increased passive tension generation by 27% compared to control fibers (P<0.001 [n=3]). Surprisingly, the LKB1/MO25/STRAD complex decreased overall tension development (14.18±2.27 mN/mm2 [n=2] vs 37.03 ± 16.72 mN/mm2 [n=9] p=0.002), and desensitized the myofilament to Ca2+ (EC50 4.18 ±0.0001 µM [n=2] vs 2.52±0.43 μM [n=9] p<0.001). In conclusion, I have shown that the functional outcomes are determined by the differential PTM patterning of cTnI. Furthermore, we have identified the LKB1/MO25/STRAD complex as a potential novel regulator of myofilament function.
- © 2013 by American Heart Association, Inc.