alexa CaMKII-dependent Troponin-I Phosphorylation Contributes To The Frequency-dependent Acceleration Of Relaxation In Ventricular Myocytes
ISSN: 2161-0665

Pediatrics & Therapeutics
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JOINT EVENT on 11th International Conference on Clinical Pediatrics & 2nd International Conference on Pediatric Surgery
June 29- July 01, 2017 London, UK

Yanggan Wang
Zhongnan Hospital of Wuhan University, China
Posters & Accepted Abstracts: Pediatr Ther
DOI: 10.4172/2161-0665-C1-040
Previous studies suggest that CaMKII activity is required for FDAR but the molecular targets remain elusive. We propose that CaMKII regulates FDAR by a mechanism that involves CaMKII-dependent alteration of myofilament sensitivity to Ca2+. [Ca2+] i and sarcomere length were measured by IonOptix Ca2+ image system. Myofilament sensitivity to Ca2+ was assessed by measuring the gradient of cell length-fura2 trajectory during contraction and late relaxation. Increasing pacing rate from 0.5 Hz to 4 Hz in left ventricular (LV) myocytes accelerated Ca2+ decline and sarcomere relaxation time constants (from 152±13 ms to 60±5 ms and from 36±2 ms to 18±1 ms, respectively, p<0.05, n=27) and increased the length-fura2 trajectory gradient (ECa50 increased from 1.62±0.06 to 1.84±0.06, p<0.05) and shifted the trajectory loop to the right, indicating a consistency of FDAR with the reduction of myofilament sensitivity to Ca2+. Inhibition of PKA (H89, 1μM) or PKC (CHE, 1μM) had no effect on myofilament Ca2+ desensitization and FDAR, whereas CaMKII inhibitor KN93 (1μM) abolished frequency-dependent myofilament desensitization to Ca2+ and FDAR. We determined the Ser23/24 phosphorylation in LV myocytes and found that Ser23/24 phosphorylation was largely reduced by PKA and PKC inhibitors but not by CaMKII inhibition. However, a phospho-Ser-antibody showed that CaMKII inhibitor KN93 significantly reduced Tn-I phosphorylation in the Tn-I immunoprecipitates, indicating that CaMKII phosphorylates Tn-I at sites different from the PKA and PKC sites. Indeed, a co-immunoprecipitation of CaMKII and Tn-I has been detected. Our results suggest that FDAR is regulated by a frequency-dependent desensitization of myofilament sensitivity to Ca2+, in which CaMKII-dependent Tn-I phosphorylation plays a major role.

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