Jones Peter P, Bazzazi Hojjat, Kargacin Gary J, Colyer John
Institute of Membrane and Systems Biology, University of Leeds, Leeds LS2 9JT, United Kingdom.
Biophys J. 2006 Jul 15;91(2):433-43. doi: 10.1529/biophysj.106.083931. Epub 2006 Apr 21.
The space between the t-tubule invagination and the sarcoplasmic reticulum (SR) membrane, the dyad, in ventricular myocytes has been predicted to experience very high [Ca2+] for short periods of time during a Ca2+ transient. The dyadic space accommodates many protein kinases responsible for the regulation of Ca2+ handling proteins of the cell. We show in vitro that cAMP-dependent protein kinase (PKA) is inhibited by high [Ca2+] through a shift in the ratio of CaATP/MgATP toward CaATP. We further generate a three-dimensional mathematical model of Ca2+ and ATP diffusion within dyad. We use this model to predict the extent to which PKA would be inhibited by an increased CaATP/MgATP ratio during a Ca2+ transient in the dyad in vivo. Our results suggest that under normal physiological conditions a myocyte paced at 1 Hz would experience up to 55% inhibition of PKA within the cardiac dyad, with inhibition averaging 5% throughout the transient, an effect which becomes more pronounced as the myocyte contractile frequency increases (at 7 Hz, PKA inhibition averages 28% across the dyad throughout the duration of a Ca2+ transient).
在心室肌细胞中，横管内陷与肌浆网（SR）膜之间的区域，即二联体，预计在钙离子瞬变期间的短时间内会经历非常高的[Ca2+]浓度。二联体区域容纳了许多负责调节细胞钙离子处理蛋白的蛋白激酶。我们在体外实验中发现，环磷酸腺苷依赖性蛋白激酶（PKA）会因高[Ca2+]浓度而受到抑制，这是通过CaATP/MgATP比值向CaATP方向转变实现的。我们进一步构建了一个关于二联体中钙离子和ATP扩散的三维数学模型。我们利用这个模型来预测在体内二联体的钙离子瞬变过程中，PKA会因CaATP/MgATP比值增加而受到抑制的程度。我们的研究结果表明，在正常生理条件下，以1赫兹频率起搏的心肌细胞，其心脏二联体中的PKA会受到高达55%的抑制，在整个瞬变过程中平均抑制率为5%，随着心肌细胞收缩频率增加，这种效应会更加明显（在7赫兹时，在钙离子瞬变的整个持续时间内，二联体中PKA的平均抑制率为28%）。
