Su Zhi, Sugishita Kazuro, Li Fenghua, Ritter Michael, Barry William H
Cardiology Division, University of Utah Health Sciences Center, Salt Lake City, Utah 84132, USA.
J Pharmacol Exp Ther. 2003 Jan;304(1):334-41. doi: 10.1124/jpet.102.041210.
FK506 binding proteins (FKBPs 12 and 12.6) interact with ryanodine receptor (RyR) and modulate its functions. FK506 binds to and reverses effects of FKBP on RyR, thus increasing RyR sensitivity to Ca2+, decreasing RyR cooperativity, and increasing RyR open probability. FK506 would thus be expected to have an effect on excitation-contraction coupling, but which of these FK506 effects predominates and how the [Ca2+]i transient would be altered are difficult to predict. FK506 has been reported to increase the [Ca2+]i transient in rat myocytes, but effects in other species have not been described. We compared the effects of FK506 on [Ca2+]i transients, L-type Ca2+ channel and Na/Ca exchange currents, membrane potential, and sarcoplasmic reticulum (SR) Ca2+ content in adult mouse and rabbit ventricular myocytes (VM). FK506 (10 microM) increased the [Ca2+]i transient in mouse VM (656 +/- 116 to 945 +/- 144 nM, p < 0.001) but decreased the amplitude of [Ca2+]i transients in rabbit VM (627 +/- 61 to 401 +/- 37 nM, p < 0.001). Similar effects were observed with rapamycin. The effects of FK506 and rapamycin on [Ca2+]i transients in VM of both species were reversible upon washout. FK506 did not alter SR Ca2+ content in mouse VM (0.79 +/- 0.1 versus 0.78 +/- 0.1 pC/pF) but reduced the SR Ca2+ content in rabbit VM (0.43 +/- 0.05 versus 0.30 +/- 0.04 pC/pF, P < 0.05) [pC = the integral (pA. s) of the caffeine-induced inward I(Na/Ca) normalized by cell capacitance (pF)]. FK506 had no effects on membrane potential, I(Ca,L) and outward I(Na/Ca) in either mouse or rabbit VM. These results indicate that alteration of the functions of RyR by FK506-mediated dissociation of FKBP from RyR has different species-dependent effects on SR Ca2+ load and thus [Ca2+]i transients. This difference may result from the fact that [Na+]i is low in rabbit myocytes, allowing extrusion by Na+/Ca2+ exchange of Ca2+ released by FK506-induced dissociation of FKBP12.6 from SR RyR.
FK506结合蛋白（FKBP12和FKBP12.6）与兰尼碱受体（RyR）相互作用并调节其功能。FK506与FKBP结合并逆转其对RyR的作用，从而增加RyR对Ca2+的敏感性，降低RyR的协同性，并增加RyR的开放概率。因此，预计FK506会对兴奋-收缩偶联产生影响，但这些FK506效应中哪一种占主导以及细胞内钙离子浓度（[Ca2+]i）瞬变将如何改变很难预测。据报道，FK506可增加大鼠心肌细胞中的[Ca2+]i瞬变，但尚未描述其在其他物种中的作用。我们比较了FK506对成年小鼠和兔心室肌细胞（VM）中[Ca2+]i瞬变、L型Ca2+通道和钠/钙交换电流、膜电位以及肌浆网（SR）Ca2+含量的影响。FK506（10 microM）增加了小鼠VM中的[Ca2+]i瞬变（从656±116 nM增加到945±144 nM，p<0.001），但降低了兔VM中[Ca2+]i瞬变的幅度（从627±61 nM降低到401±37 nM，p<0.001）。雷帕霉素也观察到类似的效应。FK506和雷帕霉素对两种物种VM中[Ca2+]i瞬变的影响在洗脱后是可逆的。FK506未改变小鼠VM中的SR Ca2+含量（0.79±0.1对0.78±0.1 pC/pF），但降低了兔VM中的SR Ca2+含量（0.43±0.05对0.30±0.04 pC/pF，P<0.05）[pC = 咖啡因诱导的内向钠/钙交换电流（I(Na/Ca)）的积分（pA·s），通过细胞电容（pF）归一化]。FK506对小鼠或兔VM中的膜电位、L型钙电流（I(Ca,L)）和外向钠/钙交换电流均无影响。这些结果表明，FK506介导的FKBP与RyR解离导致的RyR功能改变对SR Ca2+负荷以及因此对[Ca2+]i瞬变具有不同的物种依赖性效应。这种差异可能是由于兔心肌细胞中的细胞内钠离子浓度（[Na+]i）较低，使得FK506诱导的FKBP12.6从SR RyR解离释放的Ca2+能够通过钠/钙交换排出。
