Coordination between Ca2+ Release and Subsequent Re-Uptake in the Sarcoplasmic Reticulum
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- 作者：Yukio Saiki and Noriaki Ikemoto
- 刊名：Biochemistry
- 出版年：1999
- 出版时间：March 9, 1999
- 年：1999
- 卷：38
- 期：10
- 页码：3112 - 3119
- 全文大小：98K
- 年卷期：v.38,no.10(March 9, 1999)
- ISSN：1520-4995
文摘
We here report the results of our recent effort to produce, in the isolated sarcoplasmic reticulum(SR), a biphasic Ca2+ release and Ca2+ re-uptake transient and to resolve the kinetic relationship betweenCa2+ release and re-uptake of the released Ca2+. Ca2+ release from the SR was induced by polylysine(the ryanodine receptor-specific Ca2+ release trigger) at various levels of calcium loading, or at variousdoses of the trigger. The changes in the Ca2+ concentration in the reaction solution and in the lumenalCa2+ concentration were determined by stopped-flow spectroscopy using fluo-3 and mag-fura-2AM,respectively. At higher levels of calcium loading (>150 nmol/mg), polylysine induced monophasic Ca2+release curves (without an appreciable re-uptake phase) as reported in most studies in the literature.However, lowering the calcium loading level to an intermediate range (100-150 nmol/mg) produced thedesired biphasic transient curves consisting of Ca2+ release and Ca2+ re-uptake phases. Under theseconditions, the increase in the polylysine concentration resulted in the increase of both the rate of Ca2+release and that of re-uptake of the released Ca2+. The maximal rate of Ca2+ release and that of re-uptakeshowed a parallel relationship in the polylysine concentration range of 0-10 
M. This indicates thatCa2+ release from the SR and re-uptake of the released Ca2+ via the SR Ca2+ pump are well-coordinatedprocesses. The changes in the lumenal Ca2+ concentration during the release and re-uptake reaction weremonitored at an optimum level of calcium loading while clamping the extravesicular Ca2+ concentrationat a constant value. There was again a tight correlation between Ca2+ release (decrease of the lumenalCa2+ concentration) and re-uptake (increase of the lumenal Ca2+ concentration), indicating that accelerationof the re-uptake is controlled by the rate of decrease of the lumenal Ca2+ concentration. We propose thatone of the mechanisms, by which the mode of coordination between the two components of the biphasicCa2+ transient (viz. Ca2+ release via the ryanodine receptor and Ca2+ re-uptake via the SR Ca2+ pump)is controlled, is the change in the Ca2+ concentration gradient across the SR membrane.
M. This indicates thatCa2+ release from the SR and re-uptake of the released Ca2+ via the SR Ca2+ pump are well-coordinatedprocesses. The changes in the lumenal Ca2+ concentration during the release and re-uptake reaction weremonitored at an optimum level of calcium loading while clamping the extravesicular Ca2+ concentrationat a constant value. There was again a tight correlation between Ca2+ release (decrease of the lumenalCa2+ concentration) and re-uptake (increase of the lumenal Ca2+ concentration), indicating that accelerationof the re-uptake is controlled by the rate of decrease of the lumenal Ca2+ concentration. We propose thatone of the mechanisms, by which the mode of coordination between the two components of the biphasicCa2+ transient (viz. Ca2+ release via the ryanodine receptor and Ca2+ re-uptake via the SR Ca2+ pump)is controlled, is the change in the Ca2+ concentration gradient across the SR membrane.