Kameyama M, Hescheler J, Hofmann F, Trautwein W
Pflugers Arch. 1986 Aug;407(2):123-8. doi: 10.1007/BF00580662.
The calcium current (ICa) in the heart is increased by phosphorylation of a protein which is part of, or close to, the Ca channel. The phosphorylation is catalysed by cAMP-dependent protein kinase (cAMP-PK). The question whether dephosphorylated channels are available to open on depolarization was examined in ventricular myocytes of guinea pig by recording whole cell ICa during dialysis with either regulatory (R) subunit of cAMP-PK or protein kinase inhibitor (PKI) or adenosine-5'-(gamma-thio)-triphosphate (ATP gamma S). The following results were obtained: 1) R subunit reduced and PKI reversed the isoprenaline (ISP)-induced enhancement of ICa, suggesting their ability to inhibit cAMP-PK. 2) R subunit and PKI, however, reduced basal (i.e. non beta-adrenergically stimulated) ICa only by about 20%. 3) Dialysis with ATP gamma S resulted in a slow increase in basal ICa, presumably due to dephosphorylation-resistant thiophosphorylation. 4) When, however, the cell was dialyzed with PKI the effect of ATP gamma S was almost completely suppressed, suggesting no detectable phosphorylation related to the channel activity in this condition. These results support the view that even in the dephosphorylated state Ca channels are available to open on depolarization and that phosphorylation by cAMP-PK increases the opening probability.
心脏中的钙电流（ICa）会因一种蛋白质的磷酸化作用而增强，该蛋白质是钙通道的组成部分或与之紧密相关。这种磷酸化作用由环磷酸腺苷依赖性蛋白激酶（cAMP-PK）催化。通过在用cAMP-PK的调节（R）亚基、蛋白激酶抑制剂（PKI）或腺苷-5'-（γ-硫代）-三磷酸（ATPγS）进行透析期间记录豚鼠心室肌细胞的全细胞ICa，来研究去磷酸化通道在去极化时是否可用于开放。获得了以下结果：1）R亚基降低，PKI逆转了异丙肾上腺素（ISP）诱导的ICa增强，表明它们具有抑制cAMP-PK的能力。2）然而，R亚基和PKI仅使基础（即非β-肾上腺素能刺激的）ICa降低了约20%。3）用ATPγS进行透析导致基础ICa缓慢增加，推测是由于抗去磷酸化的硫代磷酸化作用。4）然而，当用PKI对细胞进行透析时，ATPγS的作用几乎被完全抑制，表明在这种情况下与通道活性相关的磷酸化作用无法检测到。这些结果支持这样一种观点，即即使处于去磷酸化状态，钙通道在去极化时也可用于开放，并且cAMP-PK的磷酸化作用会增加开放概率。
