Departments of Pharmacology, 1459 Oxford Street, PO Box 15000 Dalhousie University Halifax, Nova Scotia, Canada B3H 4R2.
Eur J Pharmacol. 2012 Sep 15;691(1-3):163-72. doi: 10.1016/j.ejphar.2012.07.012. Epub 2012 Jul 14.
This study used the selective protein kinase A (PKA) inhibitor H-89 (N-[2-(p-Bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide) to determine the role of basal PKA activity in modulating cardiac excitation-contraction coupling in the absence of β-adrenergic stimulation. Basal intracellular cyclic AMP (cAMP) levels measured in isolated murine ventricular myocytes with an enzyme immunoassay were increased upon adenylyl cyclase activation (forskolin; 1 and 10 μM) or phosphodiesterase inhibition (3-isobutyl-1-methylxanthine, IBMX; 300 μM). Forskolin and IBMX also caused concentration-dependent increases in peak Ca(2+) transients (fura-2) and cell shortening (edge-detector) measured simultaneously in field-stimulated myocytes (37 °C). Similar effects were seen upon application of dibutyryl cAMP. In voltage-clamped myocytes, H-89 (2 μM) decreased basal Ca(2+) transients, contractions and underlying Ca(2+) currents. H-89 also decreased diastolic Ca(2+) and the gain of excitation-contraction coupling (Ca(2+) release/Ca(2+) current), especially at negative membrane potentials. This was independent of alterations in sarcoplasmic reticulum (SR) Ca(2+) loading, as SR stores were unchanged by PKA inhibition. H-89 also decreased the frequency, amplitude and width of spontaneous Ca(2+) sparks measured in quiescent myocytes (loaded with fluo-4), but increased time-to-peak. Thus, H-89 suppressed SR Ca(2+) release by decreasing Ca(2+) current and by reducing the gain of excitation-contraction coupling, in part by decreasing the size of individual Ca(2+) release units. These data suggest that basal PKA activity enhances SR Ca(2+) release in the absence of ß-adrenergic stimulation. This may depress contractile function in models such as aging, where the cAMP/PKA pathway is altered due to low basal cAMP levels.
本研究使用选择性蛋白激酶 A（PKA）抑制剂 H-89（N-[2-（对溴肉桂酰胺基）乙基]-5-异喹啉磺酰胺），以确定基础 PKA 活性在缺乏β-肾上腺素能刺激的情况下调节心脏兴奋-收缩偶联的作用。用酶免疫测定法测量分离的鼠心室肌细胞中的基础细胞内环腺苷酸（cAMP）水平，在激活腺苷酸环化酶（forskolin；1 和 10 μM）或抑制磷酸二酯酶（3-异丁基-1-甲基黄嘌呤，IBMX；300 μM）时会升高。forskolin 和 IBMX 还导致同时在电场刺激的肌细胞（37°C）中测量的峰值 Ca（2+）瞬变（fura-2）和细胞缩短（边缘检测）浓度依赖性增加。应用二丁酰基 cAMP 也会产生类似的效果。在电压钳制的肌细胞中，H-89（2 μM）降低了基础 Ca（2+）瞬变、收缩和基础 Ca（2+）电流。H-89 还降低了舒张期 Ca（2+）和兴奋-收缩偶联的增益（Ca（2+）释放/Ca（2+）电流），特别是在负膜电位下。这与肌浆网（SR）Ca（2+）负载的改变无关，因为 PKA 抑制不会改变 SR 储存。H-89 还降低了在静止肌细胞（用 fluo-4 负载）中测量的自发 Ca（2+）火花的频率、幅度和宽度，但增加了峰值时间。因此，H-89 通过降低 Ca（2+）电流和降低兴奋-收缩偶联的增益来抑制 SR Ca（2+）释放，部分原因是降低了单个 Ca（2+）释放单位的大小。这些数据表明，基础 PKA 活性在缺乏β-肾上腺素能刺激的情况下增强了 SR Ca（2+）的释放。在由于基础 cAMP 水平低而导致 cAMP/PKA 途径改变的衰老等模型中，这可能会降低收缩功能。
