この記事では、ランゲンドルフ灌流ウサギの心臓における詳細なプロトコルおよび膜貫通電位 (Vm)のデュアル光学マッピングとフリーイントラ筋小胞体(SR)のために必要な機器のCa 2+を説明しています。この方法は、無傷の中心部にあるV mとSRのCa 2+動態の直接観察と定量化を可能にします。
Sarcoplasmic reticulum (SR) Ca2+ handling plays a key role in normal excitation-contraction coupling and aberrant SR Ca2+ handling is known to play a significant role in certain types of arrhythmia. Because arrhythmias are spatially distinct, emergent phenomena, they must be investigated at the tissue level. However, methods for directly probing SR Ca2+ in the intact heart remain limited. This article describes the protocol for dual optical mapping of transmembrane potential (Vm) and free intra-SR [Ca2+] ([Ca2+]SR) in the Langendorff-perfused rabbit heart. This approach takes advantage of the low-affinity Ca2+ indicator Fluo-5N, which has minimal fluorescence in the cytosol where intracellular [Ca2+] ([Ca2+]i) is relatively low but exhibits significant fluorescence in the SR lumen where [Ca2+]SR is in the millimolar range. In addition to revealing SR Ca2+ characteristics spatially across the epicardial surface of the heart, this approach has the distinct advantage of simultaneous monitoring of Vm, allowing for investigations into the bidirectional relationship between Vm and SR Ca2+ and the role of SR Ca2+ in arrhythmogenic phenomena.
Dual optical mapping of intracellular Ca2+ and transmembrane potential (Vm) in the intact Langendorff-perfused heart has become a mainstay of investigations in cardiac electrophysiology, including mechanisms of arrhythmia and excitation-contraction coupling1-4. This approach has provided unprecedented knowledge into normal and abnormal electrophysiology and, importantly, into the bidirectional relationship between Vm and intracellular Ca2+. However, optical mapping of intracellular Ca2+ with high-affinity fluorescent indicators (such as Rhod-2 and Fluo-4) only reports on bulk changes in intracellular Ca2+ and is unable to distinguish whether these changes are due to transmembrane Ca2+ flux, release and reuptake into intracellular stores, or in most instances, some combination of both. Furthermore, high-affinity Ca2+ indicators have slow on-off kinetics and may not accurately report rapid changes in Ca2+ concentration5.
Each action potential triggers a rise in intracellular Ca2+, known as the intracellular Ca2+ transient (CaT). In the mammalian heart, approximately 70 – 90% of the total CaT is due to release of Ca2+ from the sarcoplasmic reticulum (SR) via opening of ryanodine receptors (RyRs)6. Within the SR, approximately half of the total Ca2+ is bound to calsequestrin (CSQ) and other intra-SR buffers7, which play an important role in SR Ca2+ homeostasis8,9. The amount of free SR Ca2+ dictates the driving force for SR Ca2+ release as well as gating of RyR, and therefore has a significant impact on the intracellular CaT. Furthermore, alterations in SR Ca2+ release or reuptake can, in turn, impact Vm via the electrogenic Na+-Ca2+ exchange, which may have arrhythmogenic consequences. Therefore, in addition to the CaT, monitoring of free SR Ca2+ can provide important insights into contractile and electrophysiological dysfunction.
Over the past several years, investigators have made significant advances in the monitoring of SR Ca2+ in isolated cardiac myocytes and from a single location on the intact heart. One such method requires rapid pulses of caffeine to open RyRs and the SR Ca2+ content is then inferred or calculated from the immediate rise in intracellular Ca2+10. Another intriguing approach uses low-affinity Ca2+ indicators, such as Fluo-5N11 or Mag-Fluo412, which bind to free SR Ca2+. These indicators have dissociation constants (Kd) in the range of 10 – 400 μM and therefore exhibit minimal fluorescence in the cytosol compared to the SR lumen, where the Ca2+ concentration ([Ca2+]SR) is in the millimolar range. Using low-affinity Ca2+ indicators, several aspects of SR Ca2+ cycling have been investigated at the level of the isolated myocyte, including fractional SR Ca2+ release and the mechanisms of Ca2+ alternans13,14. However, in order to fully understand the heterogeneous nature of SR Ca2+ cycling in the intact heart and the role of SR Ca2+ in spatially distinct arrhythmic phenomena, methods for imaging SR Ca2+ across the epicardial surface of the intact heart are required15.
This article describes methodology for dual optical mapping of free SR Ca2+ and Vm in the intact Langendorff-perfused rabbit heart with the low-affinity Ca2+ indicator Fluo-5N. In addition to revealing SR Ca2+ characteristics spatially across the epicardial surface of the heart, this approach has the advantage of simultaneous monitoring of Vm, allowing for investigations into the bidirectional relationship between Vm and SR Ca2+.
成功のFluo-5Nの色素負荷への鍵は、色素の大量を必要とせずに高いのFluo-5N濃度を可能にする小容量循環灌流セットアップ、ロード時間(1時間)の長さ、およびロードを実行していますRTで。ロードが生理的温度、細胞の酵素活性で実行された場合、色素が細胞質ゾルに染料分子を捕捉し、それらは、SR膜を通過することができない、細胞膜を横切るときに迅速-AMタグを切断します。 RTで、しか…
The authors have nothing to disclose.
This work was supported in part by the US National Institutes of Health (R01 HL 111600) and the American Heart Association (12SDG9010015).
NaCl | Fisher Scientific | S271-1 | Component of Tyrode's solution |
CaCl2 (2H2O) | Fisher Scientific | C79-500 | Component of Tyrode's solution |
KCl | Fisher Scientific | S217-500 | Component of Tyrode's solution |
MgCl2 (6H2O) | Fisher Scientific | M33-500 | Component of Tyrode's solution |
NaH2PO4 (H2O) | Fisher Scientific | S369-500 | Component of Tyrode's solution |
NaHCO3 | Fisher Scientific | S233-3 | Component of Tyrode's solution |
D-Glucose | Fisher Scientific | D16-1 | Component of Tyrode's solution |
95% O2 5% CO2 | AirGas | carbogen | For oxygenation and pH of Tyrode's solution |
Blebbistatin | Tocris Bioscience | 1760 | Excitation-contraction uncoupler |
RH237 | Biotium | 61018 | Voltage-sensitive dye |
Fluo-5N AM | Invitrogen | F-26915 | Low-affinity Ca2+ indicator; Alternative: Invitrogen F-14204; Loading must be performed at room temperature |
Pluronic F127 | Biotium | 59004 | For Ca2+ indicator loading; Warm until the solutiion is clear before use |
Dimethyl sulphoxide (DMSO) | Sigma-Aldrich | D2650 | For dissolving blebbistatin and dyes |
Filter | EMD Millipore | NY1104700 | 11um in-line filter |
Pressure Transducer | WPI | BLPR2 | For measuring perfusion pressure |
Transbridge Transducer Amplifier | WPI | SYS-TBM4M | For transducing/amplifing pressure signal; PowerLab may also be used with appropriate BioAmp |
PowerLab 26T | ADInstruments | For continuous recording of pressure and ECG signals | |
THT Macroscope | SciMedia | Macroscopic optical setup. Details: 0.63x objective (NA=0.31), 2x condensing objective, resultant field of view = 3.1×3.1 cm, depth of focus = ~1.5mm | |
MiCam Ultima-L CMOS | SciMedia | Optical mapping cameras | |
Precision LED Spot Light | Mightex | PLS-0470-030-15-S | LED light source |