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Pflügers Archiv

, Volume 423, Issue 3–4, pp 300–306 | Cite as

Modulation of sarcoplasmic reticulum Ca2+-release channels by caffeine, Ca2+, and Mg2+ in skinned myocardial fibers of fetal and adult rats

  • Judy Y. Su
  • Yoon I. Chang
Excitable Tissues and Central Nervous Physiology

Abstract

Ryanodine causes depression of the caffeine-induced tension transient (ryanodine depression) in skinned muscle fibers, because it blocks the sarcoplasmic reticulum (SR) Ca2+-release channels [Su, J. Y. (1988) Pflügers Arch 411:132–136, 371–377; (1992) Pflügers Arch 421:1–6]. This study was performed to examine the sensitivity of SR Ca2+-release channels to ryanodine in fetal compared to adult myocardium and to investigate the influence of Ca2+, caffeine, and Mg2+ on ryanodine depression in skinned fibers. Ryanodine (0.3 nM–1 μM) caused a dose-dependent depression in skinned myocardial fibers of the rat, and the fetal fibers (IC50≈74 nM) were 26-fold less sensitive than those of the adult (IC50≈2.9 nM). The depression induced by 0.1 μM or 1 μM ryanodine was a function of [caffeine], or [Ca2+] (pCa<6.0), which was potentiated by caffeine, and an inverse function of [Mg2+]. At pCa>8.0 plus 25 mM caffeine, a 20% ryanodine depression was observed in both the fetal and adult fibers, indicating independence from Ca2+. Ryanodine depression in skinned fibers of the fetus was less affected than that seen in the adult by pCai, [caffeine]i, or 25 mM caffeine plus pCai or plus pMgi (IC50≈pCa 4.5 versus 5.1; caffeine 12.7 mM versus 2 mM; pCa 6.7 versus 7.3; and pMg 3.9 versus 3.3 respectively). The results show that the SR Ca2+-release channel in both fetal and adult myocardium is modulated by Ca2+, caffeine, and Mg2+. It is concluded that less ryanodine depression seen in the skinned fibers of the fetus, indicating a relatively insensitive SR Ca2+-release channel, could contribute to the resistance of intact myocardium to ryanodine.

Key words

Ryanodine Rat Fetus Adult Skinned myocardial fibers Caffeine Calcium Magnesium 

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Copyright information

© Springer-Verlag 1993

Authors and Affiliations

  • Judy Y. Su
    • 1
  • Yoon I. Chang
    • 1
  1. 1.Department of Anesthesiology, RN-10University of WashingtonSeattleUSA

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