Temperature dependence of macroscopic L-type calcium channel currents in single guinea pig ventricular myocytes
Temperature dependence of macroscopic L-type calcium channel currents in single guinea pig ventricular myocytes
复制标题
DOI：
10.1111/j.1540-8167.1996.tb00532.x
复制
发表时间：
1996-04-01
影响因子：
2.7
通讯作者：
Allen, TJA
中科院分区：
文献类型：
--
作者：
Allen, TJA
简介：降低温度大大减少了钙离子通过钙通道的流入。对许多组织的研究表明，峰值内向电流I-Ca表现出Q（10），值范围为1.8至3.5;然而，尚不清楚钙通道门控的哪些组分可能引起这种大的温度敏感性。可能影响通道可用性的门控组件包括磷酸化和[Ca 2 +]的变化，这些过程的相关性取决于所检查的通道。本研究解决了这个问题，通过检查温度敏感性（从34度到14摄氏度）的心脏I-Ca在控制条件下，在衰减或激活蛋白激酶A（PKA）的活性，当细胞内[Ca 2 +]已被elevated.Methods和Results：I-Ca进行了研究，使用全细胞配置的膜片钳技术。在对照中，将温度从34 ° C降低到24 ° C导致最大斜率（V-a）和峰值电流（Y-max）的电位向更正的膜电位偏移。反映可用通道数量的Y-max和宏观斜率电导（G（max））降低的Q（10）值分别为3.15 +/- 0.19和2.57 +/- 0.13。在0 mV时，Ca 2+电流呈双指数衰减，两个时间常数（tau（1）和tau（2））显示Q（10）值为1.79 +/- 0.21和2.06 +/- 0.38，而它们对总电流（I-1和I-2）的贡献显示Q（10）为5.99 +/- 0.83和1.61 +/- 0.22。在负载足以抑制I-Ca增加至1 μ M异丙肾上腺素的PKA循环抑制剂的肌细胞中，某些动力学参数的Q（10）值随着I-1的Q（10）增加至17.06 +/- 3.48而增加。通过将肌细胞暴露于1 μ M异丙肾上腺素刺激伊卡，降低了Y-max G（max）和I-1的温度敏感性，分别产生2.00 +/- 0.18、1.85 +/- 0.07和2.04 +/- 0.15的值。提高[Ca ~（2+）]（i）以增强Ca ~（2+）依赖的失活，同时影响失活和活化动力学，与对照相比，对温度敏感性影响很小。在实验条件下（2.3 ~ 2.4），达到峰值时间的Q（10）变化很小。结论：增加钙通道的磷酸化状态，而不是Ca-i（2+）依赖性失活，降低了某些门控参数的温度敏感性。这些数据表明，不可用之间的转换率，也在各种封闭状态之间的变化在相反的方向诱导的PKA依赖性磷酸化。过程，例如，抑制机制，可能涉及维持通道在不可用或“非磷酸化"状态，它可能是这些有助于宏观通道电流的高Q（10）。
Introduction: Lowering temperature greatly reduces calcium influx through calcium channels. Studies on a number of tissues demonstrate that the peak inward current, I-Ca, exhibits Q(10), values ranging from 1.8 to 3.5; however, it remains unclear which component(s) of calcium channel gating may give rise to this large temperature sensitivity. Components of gating that may affect channel availability include phosphorylation and changes in [Ca2+], processes that vary in pertinence depending on the channel examined. This study addresses this problem by examining the temperature sensitivity (from 34 degrees to 14 degrees C) of cardiac I-Ca under control conditions, during attenuation or activation of protein kinase A (PKA) activity, and when intracellular [Ca2+] has been elevated.Methods and Results: I-Ca was studied using the whole cell configuration of the patch clamp technique. In control, lowering temperature from 34 degrees to 24 degrees C resulted in a shift in the potential for maximum slope (V-a) and the peak current (Y-max) toward more positive membrane potentials. The Q(10) values for the decrease in Y-max and the macroscopic slope conductance (G(max)), which reflects the number of available channels, were 3.15 +/- 0.19 and 2.57 +/- 0.13, respectively. At 0 mV the Ca2+ current decayed biexponentially, and the two time constants (tau(1) and tau(2)) showed Q(10) values of 1.79 +/- 0.21 and 2.06 +/- 0.38, while their contribution to the total current (I-1 and I-2) showed a Q(10) of 5.99 +/- 0.83 and 1.61 +/- 0.22. In myocytes loaded with inhibitors of the PKA cycle sufficient to inhibit the increase of I-Ca to 1 mu M isoprenaline, the Q(10) values for some of the kinetic parameters were increased with the Q(10) for I-1 increasing to 17.06 +/- 3.48. Stimulation of ICa by exposing myocytes to 1 mu M isoprenaline reduced the temperature sensitivity of Y-max G(max) and I-1, yielding respective values of 2.00 +/- 0.18, 1.85 +/- 0.07, and 2.04 +/- 0.15. Raising [Ca2+](i) to enhance Ca-i(2+)-dependent inactivation, while affecting inactivation and activation kinetics, affected temperature sensitivity little compared to control. The Q(10) for time to peak changed little under experimental conditions (2.3 to 2.4).Conclusions: Increasing the phosphorylated states of calcium channels, but not Ca-i(2+)-dependent inactivation, reduces temperature sensitivity of certain gating parameters. The data suggest that the rate of the transitions between the unavailable and also between the various closed states are changed in the opposite direction to that induced by PKA-dependent phosphorylation. Processes, e.g., inhibitory mechanisms, may be involved to maintain channels in unavailable or ''unphosphorylated'' states, and it may be these that contribute to the high Q(10) of macroscopic channel currents.