Matching ATP supply and demand in cardiac pacemaker cells

匹配心脏起搏细胞中的 ATP 供应和需求

• 批准号: 8931611
• 负责人: Edward Lakatta
• 金额: $ 11.59万
• 依托单位: NATIONAL INSTITUTE ON AGING
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/8931611
• 关键词: Action Potentials; Adenosine Triphosphate; Adenylate Cyclase; Calmodulin; Cells; Consumption; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Feedback; Flavoproteins; Fluorescence; Glycolysis Inhibition; Heart; Homeostasis; Intervention; Isoproterenol; Link; Measures; Mediating; Membrane; Mitochondria; Muscle Cells; Nature; Oryctolagus cuniculus; Phosphorylation; Physiological; Production; Protein phosphatase; Proteins; Pump; Receptor Activation; Saline; Sarcoplasmic Reticulum; Signal Transduction; Sinoatrial Node; Surface; Suspension substance; Suspensions; Tissues; Ventricular; beta-adrenergic receptor; calmodulin-dependent protein kinase II; density; falls; feeding; meetings; nodal myocyte; phosphoric diester hydrolase; response

In sinoatrial node cells (SANC), Ca2+ activates adenylate cyclase (AC) to generate a high basal level of cAMP-mediated/protein kinase A (PKA)-dependent phosphorylation and Ca2+/calmodulin-dependent protein kinase II (CaMKII) protein phosphorylation of Ca2+ cycling proteins. These result in spontaneous sarcoplasmic reticulum (SR)-generated rhythmic Ca2+ oscillations during diastolic depolarization that not only trigger the surface membrane to generate rhythmic action potentials (APs), but, in a feed-forward manner, also activate AC/PKA/CaMKII signaling. ATP is consumed to pump Ca2+ to the SR, to produce cAMP, to support contraction and to maintain cell ionic homeostasis. Since feedback mechanisms link ATP-demand to ATP production, we hypothesized that (1) both basal ATP supply and demand in SANC would be Ca2+-cAMP/PKA/CaMKII dependent. (2) Due to its feed-forward nature, a decrease in flux through the Ca2+-cAMP/PKA signaling axis will reduce the basal ATP production rate. (3) Basal state calmodulin-CaMKII signaling is also linked to basal ATP production rate. SANC possess a high mitochondrial density, similar to other heart tissues O2 consumption in spontaneous beating SANC was comparable to ventricular myocytes (VM) stimulated at 3 Hz. Graded reduction of basal Ca2+-cAMP/PKA/CaMKII signaling to reduce ATP demand in rabbit SANC produced graded ATP depletion, and reduced O2 consumption and flavoprotein fluorescence. Graded reductions in basal CaMKII activity also reduced the cAMP level. In contrast to SANC, reductions in ATP demand in VM do not appreciably change the steady ATP levels. Neither inhibition of glycolysis, selectively blocking contraction nor specific inhibition of mitochondrial Ca2+ flux reduced the ATP level. We can conclude that feed-forward basal Ca2+-cAMP/PKA/CaMKII signaling both consumes ATP to drive spontaneous APs in SANC and is tightly linked to mitochondrial ATP production. Interfering with Ca2+-cAMP/PKA /CaMKII signaling not only slows the firing rate and reduces ATP consumption, but also appears to reduce ATP production so that ATP levels fall. This distinctly differs from VM, which lack this basal feed-forward basal cAMP/PKA/CaMKII signaling, and in which the ATP level remains constant when the demand changes. In response to beta-adrenergic receptor activation, the spontaneous AP firing rate and the demand for ATP increase. To increase ATP demand, single isolated rabbit SANC were superfused by physiological saline at 350.5C with isoproterenol, or by phosphodiesterase or protein phosphatase inhibition. We measured cytosolic and mitochondrial Ca2+ and flavoprotein fluorescence in single SANC and we measured cAMP, ATP and O2 consumption in SANC suspensions. Although the increase in spontaneous AP firing rate was accompanied by an increase in O2 consumption, the ATP level and flavoprotein fluorescence remained constant, indicating that ATP production had increased. Both Ca2+m and cAMP increased concurrently with the increase in AP firing rate. When Ca2+m was reduced by Ru360, the increase in spontaneous AP firing rate in response to isoproterenol was reduced by 25%. Thus, both an increase in Ca2+m and an increase in Ca2+ activated cAMP-PKA-CaMKII signaling regulate the increase in ATP supply to meet ATP demand above the basal level.

在窦房结细胞（SANC）中，Ca 2+激活腺苷酸环化酶（AC）以产生高基础水平的cAMP介导的/蛋白激酶A（PKA）依赖性磷酸化和Ca 2 +/钙调蛋白依赖性蛋白激酶II（CaMKII）蛋白磷酸化的Ca 2+循环蛋白。这些导致在舒张期去极化期间自发肌浆网（SR）产生的节律性Ca 2+振荡，其不仅触发表面膜产生节律性动作电位（AP），而且以前馈方式激活AC/PKA/CaMKII信号传导。消耗ATP以将Ca 2+泵送到SR，产生cAMP，支持收缩并维持细胞离子稳态。由于反馈机制将ATP需求与ATP产生联系起来，我们假设（1）SANC中的基础ATP供应和需求都是Ca 2 +-cAMP/PKA/CaMK II依赖性的。(2)由于其前馈性质，通过Ca 2 +-cAMP/PKA信号传导轴的流量减少将降低基础ATP产生速率。(3)基础状态钙调素-CaMKII信号传导也与基础ATP产生速率相关。SANC具有与其他心脏组织相似的高线粒体密度，在自发搏动中SANC的O2消耗与在3 Hz下刺激的心室肌细胞（VM）相当。在兔SANC中，基础Ca 2 +-cAMP/PKA/CaMKII信号传导的分级减少以减少ATP需求，产生分级的ATP消耗，并减少O2消耗和黄素蛋白荧光。基础CaMKII活性的分级降低也降低了cAMP水平。与SANC相反，VM中ATP需求的减少不会明显改变稳定的ATP水平。无论是抑制糖酵解，选择性阻断收缩，也没有特定的抑制线粒体Ca 2+流量降低ATP水平。我们可以得出结论，前馈基础Ca 2 +-cAMP/PKA/CaMKII信号转导既消耗ATP以驱动SANC中的自发AP，又与线粒体ATP产生紧密相关。干扰Ca 2 +-cAMP/PKA /CaMKII信号传导不仅减慢了放电速率并减少了ATP消耗，而且似乎还减少了ATP的产生，从而使ATP水平下降。这与VM明显不同，VM缺乏这种基础前馈基础cAMP/PKA/CaMKII信号传导，并且其中ATP水平在需求变化时保持恒定。 响应于β-肾上腺素能受体激活，自发AP放电率和对ATP的需求增加。为了增加ATP需求，将单个分离的兔SANC用含异丙肾上腺素的350.5 ℃生理盐水或磷酸二酯酶或蛋白磷酸酶抑制剂灌流。我们测量了单个SANC的胞浆和线粒体Ca 2+和黄素蛋白荧光，并测量了SANC悬浮液中的cAMP、ATP和O2消耗。虽然自发AP放电率的增加伴随着O2消耗的增加，但ATP水平和黄素蛋白荧光保持不变，表明ATP产生增加。Ca ~（2+）m和cAMP均随AP放电频率的增加而增加。当Ru 360降低Ca 2 +m时，响应于异丙肾上腺素的自发AP放电率的增加减少了25%。因此，Ca 2 +m的增加和Ca 2+激活的cAMP-PKA-CaMK II信号传导的增加调节ATP供应的增加以满足高于基础水平的ATP需求。