論文 - 佐藤　達也

The beginning of the calcium transient in rat embryonic heart.

Takeshi Kobayashi, Sachiko Maeda, Nobutoshi Ichise, Tatsuya Sato, Takehito Iwase, Sumihiko Seki, Yoichi Yamada, Noritsugu Tohse

The journal of physiological sciences : JPS   61 ( 2 ) 141 - 9  2011年03月  [査読有り]  [国内誌]

　概要を見る

Although many researchers have tried to observe the beginning of the heartbeat, no study has shown the beginning of the calcium transient. Here, we evaluate the beginning of the calcium transient in the Wistar rat heart. We first tried to reveal when the heart of the Wistar rat begins to contract because no previous study has evaluated the beginning of the heartbeat in Wistar rats. Observation of embryos transferred to a small incubator mounted on a microscope revealed that the heart primordium, the so-called cardiac crescent, began to contract at embryonic day 9.99-10.13. Observation of embryos loaded with fluo-3 AM revealed that the beginning of the calcium transient precedes the initiation of contraction which precedes the appearance of the linear heart tube. Nifedipine (1 μM), but not ryanodine (1 μM), abolished the calcium transients. These results indicate that calcium transients in the early embryonic period involve exclusively calcium entry through L-type calcium channels in contrast to the situation in mature hearts. This study provides the first demonstration of the relationship between morphological changes in the heart primordium and the beginning of the calcium transient and contraction.

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Hypertensive hypertrophied myocardium is vulnerable to infarction and refractory to erythropoietin-induced protection.

Toshiyuki Yano, Takayuki Miki, Masaya Tanno, Atsushi Kuno, Takahito Itoh, Akifumi Takada, Tatsuya Sato, Hidemichi Kouzu, Kazuaki Shimamoto, Tetsuji Miura

Hypertension (Dallas, Tex. : 1979)   57 ( 1 ) 110 - 5  2011年01月  [査読有り]  [国際誌]

　概要を見る

The objective of this study was to examine the hypothesis that hypertensive hypertrophy is vulnerable to infarction and defective in cytoprotective mechanisms by modification of intracellular signaling and mitochondrial proteins. Myocardial infarction was induced by 20-minute coronary occlusion/reperfusion in spontaneously hypertensive stroke-prone rats (SHR-SPs) and their controls (Wistar-Kyoto rats [WKYs]). Infarct size expressed as a percentage of area-at-risk was larger by 29% in SHR-SPs than in WKYs. Pretreatment with erythropoietin (EPO) significantly limited infarct size in WKYs but not in SHR-SPs. Ca(2+) retention capacity of mitochondria, an index of the threshold for opening of the mitochondrial permeability transition pore, on reperfusion was reduced in SHR-SPs compared with that in WKYs. Suppression of reactive oxygen species by N-(2-mercaptopropionyl)-glycine increased Ca(2+) retention capacity after reperfusion and limited infarct size in SHR-SPs to levels in WKYs. EPO induced phosphorylation of Akt, extracellular signal-related kinase, and glycogen synthase kinase-3β in the myocardium in both WKYs and SHR-SPs. EPO enhanced interaction of phospho-glycogen synthase kinase-3β and adenine nucleotide translocase on reperfusion in WKYs, although such an effect of EPO was not detected in SHR-SPs. The results suggest that enhanced opening of mitochondrial permeability transition pores by reactive oxygen species and modification of the signal downstream of phospho-glycogen synthase kinase-3β in the mitochondria underlie the increased vulnerability to infarction and the lack of anti-infarct tolerance by EPO, respectively, in hypertensive hypertrophied hearts.

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Erythropoietin (EPO) affords more potent cardioprotection by activation of distinct signaling to mitochondrial kinases compared with carbamylated EPO.

Yoshiaki Terashima, Tatsuya Sato, Toshiyuki Yano, Ole Maas, Takahito Itoh, Takayuki Miki, Masaya Tanno, Atsushi Kuno, Kazuaki Shimamoto, Tetsuji Miura

Cardiovascular drugs and therapy   24 ( 5-6 ) 401 - 8  2010年12月  [査読有り]  [国際誌]

　概要を見る

PURPOSE: Erythropoietin (EPO) and its non-erythrogenic derivative, carbarmylated EPO (CEPO), have been reported to activate different receptors (homomeric EPO receptor vs. heteromeric receptor consisting of EPO receptor monomer and common β-subunit). The aim of this study was to examine differences between EPO and CEPO in efficacy of cardioprotection against infarction and in activation of pro-survival kinases. METHODS: In isolated rat hearts, infarction was induced by global ischemia followed by reperfusion. Infarct size was determined 2 h after reperfusion, and ventricular tissues for immunoblotting were sampled at 5 min after reperfusion. RESULTS: Pretreatment with EPO (10 units/ml) before ischemia reduced infarct size (% of risk area; %IS/AR) from 47.0 ± 2.1% of the control after 20-min ischemia to 24.7 ± 4.3% and from 62.0 ± 3.0% after 25-min ischemia to 45.5 ± 4.1%. Desialylated EPO (asialoEPO, 100 ng/ml) mimicked the protection by EPO. However, CEPO (100 ng/ml) failed to reduce infarct size after 20-min ischemia (%IS/AR = 47.5 ± 5.9%) and that after 25-min ischemia (%IS/AR = 56.1 ± 4.2%). The infarct size-limiting effect of CEPO was not shown either by increasing CEPO dose to 500 ng/ml or by shortening ischemia to 15 min. Both EPO and CEPO enhanced phosphorylation of cytosolic GSK-3β upon reperfusion. In contrast, phosphorylation of GSK-3β, Akt, and PKC-ε in mitochondria upon reperfusion was significantly enhanced by EPO but not by CEPO. CONCLUSION: EPO affords more potent protection against infarction than does CEPO by distinct activation of signaling leading to phosphorylation of pro-survival protein kinases in mitochondria upon reperfusion.

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Mitochondrial kinase signalling pathways in myocardial protection from ischaemia/reperfusion-induced necrosis.

Tetsuji Miura, Masaya Tanno, Tatsuya Sato

Cardiovascular research   88 ( 1 ) 7 - 15  2010年10月  [査読有り]  [国際誌]

　概要を見る

Multiple cardioprotective signal pathways that are activated by ischaemic preconditioning (IPC) and those by IPC mimetics converge on mitochondria. Recent studies have shown that pools of Akt, protein kinase C-ε, extracellular-regulated kinases, glycogen synthase kinase-3beta (GSK-3beta), and hexokinases (HK) I and II, are localized in mitochondria in addition to their pools in the cytosol. Accumulating evidence indicates that such 'mitochondrial protein kinases' receive signals from cytosolic molecules and enhance tolerance of myocytes to injury. Proteomic analyses suggest that these kinases form complexes with each other and with subunit proteins of the mitochondrial permeability transition pore (mPTP). Functional relationships between the protein kinases in mitochondria have not been fully clarified, but GSK-3beta and HKs appear to be at the end of the signal pathways and directly responsible for inhibition of opening of the mPTP and, thus, for myocyte protection from necrosis. In this review, recent findings supporting roles of mitochondrial protein kinases in protection from myocardial necrosis after ischaemia/reperfusion are summarized and discussed.

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