Studies on the Roles of $Na^+\;-Ca^{2+}$ Exchange according to Postnatal Age in the Negative Staircase Effect of the Rat Heart

흰쥐 심근의 역 사다리 효과에 있어서 생후 연령에 따른 $Na^+\;-Ca^{2+}$ 교환의 역할에 관한 연구

  • Lee, Hae-Yong (Department of Pediatrics, Wonju-College of Medicine and Institute of Basical Medicine, Yonsei University) ;
  • Kim, Soon-Jin (Department of Pharmacology, Wonju-College of Medicine and Institute of Basical Medicine, Yonsei University) ;
  • Ko, Chang-Mann (Department of Pharmacology, Wonju-College of Medicine and Institute of Basical Medicine, Yonsei University)
  • 이해용 (연세대학교 원주의과대학 소아과학교실, 기초의학 연구소) ;
  • 김순진 (연세대학교 원주의과대학 약리학교실 및 기초의학 연구소) ;
  • 고창만 (연세대학교 원주의과대학 약리학교실 및 기초의학 연구소)
  • Published : 1997.12.21

Abstract

Recent reports revealed that the $Na^+-Ca^{2+}$ exchangers and feet structures of sarcoplasmic reticulum(SR) are located in close vicinity in the specific compartment. Therefore, we investigated the possibility that the $Na^+-Ca^{2+}$ exchanger may decrease the tension development by transporting the $Ca^{2+}$ out of the cell right after it released from SR, on the basis of this anatomical proximity. We exammined the negative force-frequency relationship of the developed tension in the electrically field stimulated left atria of postnatal developing rat(1, 3 day, 1 week and 4 week old after birth). Cyclopiazonic $acid(3{\times}10^{-5}\;M)$ treatment decreased the developed tension further according to postnatal age. $Monensin(3{\times}10^{-6}\;M)$ treatment did not increase the maximal tension in 4 week-old rat, preserving negative staircase, while the negative staircase in the younger rat were flattened. $Ca^{2+}$ depletion in the buffer elicited more suppression of the maximal tension according to the frequency in all groups except the 4 week-old group. The % decrease of the maximal developed tension of 4 week-old group at 1 Hz to that of 0.1 Hz after $Na^+$ and $Ca^{2+}$ depletion was only a half of those of the yonger groups. Taken together, it is concluded that the $Na^+-Ca^{2+}$ exchange transports more $Ca^{2+}$ released from SR out of the cell in proportion to the frequency, and this is responsible for the negative staircase effect of the rat heart.

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