2004 Fiscal Year Final Research Report Summary
Study for detection of intracellular sodium transients and their pathophysiological roles in myocytes
| Project/Area Number |
15590733
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Circulatory organs internal medicine
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| Research Institution | Hamamatsu University School of Medicine |
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Principal Investigator |
SATOH Hiroshi Hamamatsu University School of Medicine, Department of Medicine, Research Associate, 医学部附属病院, 助手 (30293632)
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| Co-Investigator(Kenkyū-buntansha) |
KATOH Hideki Hamamatsu University School of Medicine, Department of Medicine, Research Associate, 医学部, 助手 (80314029)
TERADA Hajime Hamamatsu University School of Medicine, Department of Medicine, Research Associate, 医学部附属病院, 講師 (50252177)
URUSHIDA Tsuyoshi Hamamatsu University School of Medicine, Department of Medicine, Research Associate, 医学部附属病院, 助手 (20334980)
WATANABE Yasuhide Hamamatsu University School of Medicine, Department of Nursing, Professor, 医学部, 教授 (50305380)
HAYASHI Hideharu Hamamatsu University School of Medicine, Department of Medicine, Professor, 医学部, 教授 (50135258)
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| Project Period (FY) |
2003 – 2004
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| Keywords | Sodium ion / Calcium ion / Myocytes / Na^+ / Ca^<2+> exchange / Excitation-contraction coupling |
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| Research Abstract |
In cardiac myocytes the Ca^<2+>-induced Ca^<2+> release (CICR) from the sarcoplasmicr reticulum (SR) plays pivotal roles in Ca transients. However, the changes in intracellular Na^+ concentration ([Na^+]_i) also contribute significantly to CICR via Na^+/Ca^<2+> exchange. The negative inotropic effect of Na^+ channel blockers (NCB) is mediated by disturbance of intracellular Ca^<2+> regulation. The Na^+ channel gating could induce intracellular Na^+ accumulation, thereby increasing Ca^<2+> influx via the reverse-mode Na^+/Ca^<2+> exchange (rNCX). The primary aim of this study was to investigate whether the reduction of cellular Na^+ accumulation by NCB actually contributes to the negative inotropic effects through the elimination of Ca^<2+> influx via rNCX. To elucidate the involvement of rNCX in the negative inotropic effects of Na^+ channel blockers, we examined the effects of a pure Na^+ channel blocker, pilsicainide, on the frequency-dependent increases in twitch cell shortenings (C
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S) and Ca^<2+> transients (CaT) in Indo-1 or fluo-3 loaded guinea pig ventricular myocytes. The changes in [Na^+]_i was also evaluated with Sodium-Green and laser scanning confocal microscopy. Na^+/Ca^<2+> exchange current (I_<NCX>) was measured by the whole cell patch clamp method. (1) Pilsicainide (>5 μM) significantly reduced CaT at all stimulation rates, and the reduction was more prominent use-dependently (p<0.05 vs. control, n=7). (2) An inhibitor of rNCX, 1 μM KB-R7943 decreased CS and CaT only at 2 Hz (peak indo-1 ratio ; from 1.02±0.13 to 0.98±0.11 at 0.5 Hz, n.s., 1.96±0.11 to 1.45±0.11 at 2 Hz, p<0.05, n=7). (3) On diminishing CS and CaT by 30 μM plisicainide at 2 Hz, the following addition of 1 μM KB-R7943 had no further effects. (4) 100 μM Pilsicainide did not affect to I_<NCX>. (5) The significant cytosolic Na^+ accumulation was observed only at 2 Hz in control, and Pilsicainide suppressed the accumulation in [Na^+]_i dose-dependently at 2 Hz. (p<0.05 vs. control, n=5). The negative inotropic effects of NCB could involve the reduction of Ca^<2+> influx via rNCX by preventing cytosolic (not only subsarcolemmal) Na^+ accumulation. The mechanism would have a more important implication in failed heart with tachyarrhythmia. Less
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