Chen Y H, DeHaan R L
Department of Anatomy and Cell Biology, Emory University Health Science Center, Atlanta, Georgia 30322.
J Membr Biol. 1993 Nov;136(2):125-34. doi: 10.1007/BF02505757.
We have investigated the effects of temperature on the conductance and voltage-dependent kinetics of cardiac gap junction channels between pairs of seven-day embryonic chick ventricle myocytes over the range of 14-26 degrees C. Records of junctional conductance (Gj) and steady-state unit junctional channel activity were made using the whole-cell double patch-clamp technique while the bath temperature was steadily changed at a rate of about 4 degrees C/min. The decrease in Gj upon cooling was biphasic with a distinct break at 21 degrees C. In 12 cell pairs, Q10 was 2.2 from 26 to 21 degrees C, while between 21 and 14 degrees C it was 6.5. The mean Gj at 22 degrees C (Gj22) was 3.0 +/- 2.1 nS, ranging in different preparations from 0.24 to 6.4 nS. At room temperature, embryonic cardiac gap junctions contain channels with conductance states near 240, 200, 160, 120, 80 and 40 pS. In the present study, we demonstrate that cooling decreases the frequency of channel openings at all conductance levels, and at temperatures below 20 degrees C shifts the prevalence of openings from higher to lower conductance states: all 240 pS openings disappear below 20 degrees C; 200 pS openings are suppressed at 17 degrees C; below 16 degrees C 160 and 120 pS events disappear and only 80 and 40 pS states are seen. Temperature also affected the voltage-dependent kinetics of the channels. Application of a 6 sec, 80 mV voltage step across the junction (Vj80) caused a biexponential decay in junctional conductance. Decay was faster at lower temperatures, whereas the rate of recovery of Gj after returning to Vj0 was slowed. Cooling reduced the fast decay time constant, increased both recovery time constants, and decreased the magnitude of Gj decay, thus leaving a 10-16% larger residual conductance (Gss/Ginit, +/- 80 mV Vj) at 18 than at 22 degrees C. From these results we propose that embryonic chick cardiac gap junctions contain at least two classes of channels with different conductances and temperature sensitivities.
我们研究了温度对7日龄鸡胚心室肌细胞对之间心脏缝隙连接通道电导和电压依赖性动力学的影响，温度范围为14至26摄氏度。使用全细胞双膜片钳技术记录连接电导（Gj）和稳态单位连接通道活性，同时以约4摄氏度/分钟的速率稳定改变浴温。冷却时Gj的降低是双相的，在21摄氏度处有明显的断点。在12个细胞对中，26至21摄氏度时Q10为2.2，而21至14摄氏度时为6.5。22摄氏度时的平均Gj（Gj22）为3.0±2.1 nS，不同制剂中的范围为0.24至6.4 nS。在室温下，胚胎心脏缝隙连接包含电导状态接近240、200、160、120、80和40 pS的通道。在本研究中，我们证明冷却会降低所有电导水平下通道开放的频率，并且在低于20摄氏度的温度下，开放的发生率会从高电导状态转变为低电导状态：所有240 pS的开放在低于20摄氏度时消失；200 pS的开放在17摄氏度时受到抑制；低于16摄氏度时，160和120 pS的事件消失，仅可见80和40 pS的状态。温度也影响通道的电压依赖性动力学。在连接处施加6秒、80 mV的电压阶跃（Vj80）会导致连接电导呈双指数衰减。在较低温度下衰减更快，而回到Vj0后Gj的恢复速率减慢。冷却降低了快速衰减时间常数，增加了两个恢复时间常数，并降低了Gj衰减的幅度，因此在18摄氏度时留下的残余电导（Gss/Ginit，±80 mV Vj）比在22摄氏度时大10 - 16%。从这些结果我们提出，鸡胚心脏缝隙连接至少包含两类具有不同电导和温度敏感性的通道。
