Hui C S
Department of Physiology and Biophysics, Indiana University Medical Center, Indianapolis 46223.
J Gen Physiol. 1991 Aug;98(2):287-314. doi: 10.1085/jgp.98.2.287.
Charge movements were measured in frog intact fibers with the three-microelectrode technique and in cut fibers with the double Vaseline gap technique. At 13-14 degrees C, the ON segments of charge movement records from both preparations showed an early I beta component and a late I gamma hump component. When an intact fiber was cooled to 4-7 degrees C, the time-to-peak of I gamma (tp,gamma) was prolonged, but I gamma still appeared as a hump. Q-V plots from intact fibers at 4-7 degrees C were fitted with a sum of two Boltzmann distribution functions (method 1). The more steeply voltage-dependent component, identified with Q gamma, accounted for 32.1% (SEM 2.2%) of the total charge. This fraction was larger than the 22.6% (SEM 1.5%) obtained by separating the ON currents with a sum of two kinetic functions (method 2). The total charge in cut fibers stretched to a sarcomere length of 3.5 microns at 13-14 degrees C was separated into Q beta and Q gamma by methods 1 and 2. The fraction of Q gamma in the total charge was 51.3% (SEM 1.7%) and 53.7% (SEM 1.8%), respectively, suggesting that cut fibers have a larger proportion of Q gamma:Q beta than intact fibers. When cut fibers were stretched to a sarcomere length of 4 microns, the proportion of Q gamma:Q beta was unchanged. Between 4 and 13 degrees C, the Q10 of l/tp,gamma in intact fibers was 2.33 (SEM 0.33) and that of 1/tau beta was less than 1.44 (SEM 0.04), implying that the kinetics of I gamma has a steeper temperature dependence than the kinetics of I beta. When cut fibers were cooled from 14 to 6 degrees C, I gamma in the ON segment generally became too broad to be manifested as a hump. In a cut fiber in which I gamma was manifested as a hump, the Q10 of l/tp,gamma was 2.08 and that of l/tau beta was less than 1.47. Separating the Q-V plots from cut fibers at different temperatures by method 1 showed that the proportion of Q gamma:Q beta was unaffected by temperature change. The appearance of I gamma humps at low temperatures in intact fibers but generally not in cut fibers suggests an intrinsic difference between the two fiber preparations.
采用三微电极技术在完整的蛙肌纤维中以及采用双凡士林间隙技术在切断的肌纤维中测量电荷移动。在13 - 14℃时，两种标本的电荷移动记录的开启段均显示出早期的Iβ成分和晚期的Iγ驼峰成分。当完整肌纤维冷却至4 - 7℃时，Iγ的峰值时间（tp,γ）延长，但Iγ仍表现为驼峰。4 - 7℃下完整肌纤维的Q - V曲线用两个玻尔兹曼分布函数之和拟合（方法1）。与Qγ相关的电压依赖性更强的成分占总电荷量的32.1%（标准误2.2%）。该比例大于用两个动力学函数之和分离开启电流所得到的22.6%（标准误1.5%）（方法2）。在13 - 14℃下将切断的肌纤维拉伸至肌节长度为3.5微米时，通过方法1和方法2将总电荷分离为Qβ和Qγ。Qγ在总电荷中的比例分别为51.3%（标准误1.7%）和53.7%（标准误1.8%），表明切断肌纤维中Qγ:Qβ的比例高于完整肌纤维。当切断肌纤维拉伸至肌节长度为4微米时，Qγ:Qβ的比例不变。在4至13℃之间，完整肌纤维中1/tp,γ的Q10为2.33（标准误0.33），1/τβ的Q10小于1.44（标准误0.04），这意味着Iγ的动力学比Iβ的动力学具有更陡峭的温度依赖性。当切断肌纤维从14℃冷却至6℃时，开启段的Iγ通常变得过宽而无法表现为驼峰。在一根Iγ表现为驼峰的切断肌纤维中，1/tp,γ的Q10为2.08，1/τβ的Q10小于1.47。用方法1分离不同温度下切断肌纤维的Q - V曲线表明，Qγ:Qβ的比例不受温度变化的影响。完整肌纤维在低温下出现Iγ驼峰而切断肌纤维一般不出现，这表明两种肌纤维标本存在内在差异。
