A single glass micropipette voltage clamp technique with intracellular dialysis was used to study Ba2+ currents in isolated ventricular cells from guinea-pig hearts. Effects of the 1,4-dihydropyridine Bay K 8644 on whole-cell currents were evaluated at 37 degrees C. 2. Bay K 8644 increased the Ba2+ peak currents at test potentials between -50 and +20 mV and shifted the current-voltage relationships towards hyperpolarizing potentials (leftward shift for Ca2+ channel activation, 13.8 +/- 4.1 mV; n = 9; Bay K 8644, 5 mumol/l). 3. The peak times of the Ba2+ currents were diminished over the voltage range tested between -40 and +20 mV after Bay K 8644 in parallel with a shortening of the time constant of activation that was estimated from fits of the recorded currents with a d2f model. 4. The decay of the Ba2+ currents was fitted with two exponentials including a pedestal. The compound Bay K 8644 accelerated the fast decay over the whole voltage range. The amplitude of the rapidly inactivated component of the Ba2+ currents was strikingly increased after application of Bay K 8644. 5. The steady-state inactivation using a 0.5 or 5 s pre-pulse was shifted towards hyperpolarizing potentials (leftward shift 10.3 +/- 5.2 mV; n = 4; Bay K 8644, 5 mumol/l). 6. The change in the time course of Bay K 8644-modified Ba2+ currents cannot be described solely by a decrease of the backward rate coefficient from an open to a closed state of the Ca2+ channel (Sanguinetti, Krafte & Kass, 1986). The described effects of Bay K 8644 on the inactivation can be both qualitatively and quantitatively described by a model of current-dependent inactivation (Standen & Stanfield, 1982), assuming a lower affinity of an internal binding site for Ba2+ than for Ca2+.
摘要
采用细胞内透析的单玻璃微吸管电压钳技术，研究豚鼠心脏分离心室细胞中的Ba2+电流。在37℃下评估1,4-二氢吡啶类药物Bay K 8644对全细胞电流的影响。2. Bay K 8644使测试电位在-50至+20 mV之间时的Ba2+峰值电流增加，并使电流-电压关系向超极化电位方向移动（Ca2+通道激活向左移位，13.8±4.1 mV；n = 9；Bay K 8644，5 μmol/l）。3. 在Bay K 8644作用后，在-40至+20 mV测试电压范围内，Ba2+电流的峰值时间缩短，同时根据记录电流与d2f模型拟合估算的激活时间常数也缩短。4. Ba2+电流的衰减用包含一个平台的两个指数函数拟合。复合药物Bay K 8644在整个电压范围内加速了快速衰减。应用Bay K 8644后，Ba2+电流快速失活成分的幅度显著增加。5. 使用0.5或5 s预脉冲的稳态失活向超极化电位方向移动（向左移位10.3±5.2 mV；n = 4；Bay K 8644，5 μmol/l）。6. Bay K 8644修饰的Ba2+电流时间进程的变化不能仅通过Ca2+通道从开放状态到关闭状态的反向速率系数降低来描述（Sanguinetti、Krafte和Kass，1986）。假设内部结合位点对Ba2+的亲和力低于对Ca2+的亲和力，则电流依赖性失活模型可以定性和定量地描述Bay K 8644对失活的上述影响（Standen和Stanfield，1982）。
