| Budget Amount *help |
¥4,010,000 (Direct Cost: ¥3,500,000、Indirect Cost: ¥510,000)
Fiscal Year 2007: ¥2,210,000 (Direct Cost: ¥1,700,000、Indirect Cost: ¥510,000)
Fiscal Year 2006: ¥1,800,000 (Direct Cost: ¥1,800,000)
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| Research Abstract |
Recent studies have shown that the impairment of L-type Ca^<2+> channel function is associated with arrhythmia such as atrial fibrillation. Aiming at clarifying the signaling molecular complex involved in the regulation of L-type Ca^<2+> channel in atria (calcium signalosome), we screened proteins associated with the carboxyl terminal region of Cav1.2. We found that the C-terminal region of Cav1.2 interacts with phosphatidylcholine transfer protein-like protein (PCTP-USTARD10). PCTP-L was expressed in embryonic whole heart and, in adult heart, in atria but not in ventricle. In rat atrial myocytes, PCTP-L colocalized and was coimmunoprecipitated with Cav1.2. PCTP-L attenuated the voltage-dependent inactivation of Cav1.2 through the specific interaction with the C-terminal region of Cav1.2. In the present study, our findings are as follows :
1) The knockdown of PCTP-L by RNAi, in atrial myocytes, resulted in the shorteningof action potential duration and an increase in the frequency of sp
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ontaneous action potentials as well as Ca^<2+> transients. In addition, in atria of pressure-overloaded atrial fibrillation model rats, the mRNA expression level of PCTP-L was significantly reduced. These results suggest that PCTP-L is involved in the regulation of the excitability of atrial myocytes.
2) To elucidate the role of Cav1.3, an atrial-specific subtype of L-type Ca^<2+> channels, we compared the electrophysiological properties with those of Cav1.2. In addition to lower voltage-dependence of activation and inactivation, Cav1.3 exibited slower voltage-dependent inactivation (VDI) and faster recovery from the inactivation compared to Cav1.2. Under voltage-clamp with SA nodal pacemaker action potential (AP) waveform, Cav1.3 current activated during diastolic depolarization and reactivated during repolarizing phase, while Cav1.2 current activated at the threshold of AR. Under repetitive depolarization, Cav1.3 maintained higher availability than Cav1.2. Computer simulation indicates that slow VDI and fast recovery kinetics of Cav1.3 contribute to maintain its availability under repetitive depolarizarion in SA node.
3) The functional interaction between Cav1.2 and PCTP-L was impaired by replacing the C-terminal region of Cav1.2 by the comparable region of Cav1.3, thus indicating that PCTP-L interacts with Cav1.2 in a subtype-specific manner.
4) ln order to clarify thefunctional role of PCTP-L in the Ca^<2+> signalosome surrounding the L-type Ca^<2+> channel in atria, we generated PCTP-L-KO mice. Phenotypes of PCTP-L-KO mice are under investigation. Less
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