Ca²⁺-activated adenylyl cyclase 1 introduces Ca²⁺-dependence to beta-adrenergic stimulation of HCN2 current

详细信息	查看全文 | 推荐本文 |

• 作者：Yelena N. Kryukova^a ; Lev Protas^a ; Richard B. Robinson^a ; ^b ; ^{rbr1@columbia.edu}
• 关键词：Hyperpolarization-activated channels ; Cardiac myocytes ; cAMP ; Adenylyl cyclase ; Adrenergic modulation
• 刊名：Journal of Molecular and Cellular Cardiology
• 出版年：2012
• 期刊代码：171_00222828
• 类别：bio
• 出版时间：June, 2012
• 卷：52
• 期：6
• 页码：1233-1239
• 文件大小：636 K

摘要

Previous observations show that 尾-adrenergic modulation of pacemaker current (I_f) in sinoatrial node (SAN) cells is impaired by disruption of normal Ca²⁺-homeostasis with ryanodine or BAPTA. Recently, the presence of Ca²⁺-activated adenylyl cyclase (AC) 1 was reported in SAN, and was proposed as a possible mechanism of Ca²⁺-dependence of 尾-adrenergic modulation. However, direct evidence that pacemaker (HCN) channels can be regulated by Ca²⁺-activated AC and that such regulation introduces Ca²⁺ dependence, is lacking. Here we co-expressed AC1 or AC6 with HCN2 in neonatal rat ventricular myocytes, which lack AC1. Although both isoforms have equivalent expression level and ability to interact with HCN2, only AC1 increases intracellular cAMP content, accelerates spontaneous beating rate and modifies HCN2 biophysics. Measured HCN2 current in the AC1 group activated ~ 10 mV more positive than in GFP or AC6. The 尾-adrenergic agonist isoproterenol induced a further positive shift under control conditions, but failed to do so after pretreatment with the Ca²⁺ chelator BAPTA. In the AC6 group, isoproterenol shifted the HCN2 activation relation to a similar extent in the absence and presence of BAPTA. Thus, AC1 but not AC6 over-expression introduces Ca²⁺-sensitivity to the 尾-adrenergic response of HCN2. These results demonstrate physical and functional interaction between AC isoforms and the HCN2 pacemaker channel and support a key role of Ca²⁺ activated AC1 as a molecular mechanism in Ca²⁺-dependent modulation of 尾-adrenergic response of heart rate.