Wang H Z, Li J, Lemanski L F, Veenstra R D
Department of Pharmacology, State University of New York Health Science Center, Syracuse 13210.
Biophys J. 1992 Jul;63(1):139-51. doi: 10.1016/S0006-3495(92)81573-4.
Numerous two-cell voltage-clamp studies have concluded that the electrical conductance of mammalian cardiac gap junctions is not modulated by the transjunctional voltage (Vj) profile, although gap junction channels between low conductance pairs of neonatal rat ventricular myocytes are reported to exhibit Vj-dependent behavior. In this study, the dependence of macroscopic gap junctional conductance (gj) on transjunctional voltage was quantitatively examined in paired 3-d neonatal hamster ventricular myocytes using the double whole-cell patch-clamp technique. Immunolocalization with a site-specific antiserum directed against amino acids 252-271 of rat connexin43, a 43-kD gap junction protein as predicted from its cDNA sequence, specifically stained zones of contact between cultured myocytes. Instantaneous current-voltage (Ij-Vj) relationships of neonatal hamster myocyte pairs were linear over the entire voltage range examined (0 less than or equal to Vj less than or equal to +/- 100 mV). However, the steady-state Ij-Vj relationship was nonlinear for Vj greater than +/- 50 mV. Both inactivation and recovery processes followed single exponential time courses (tau inactivation = 100-1,000 ms, tau recovery approximately equal to 300 ms). However, Ij recovered rapidly upon polarity reversal. The normalized steady-state junctional conductance-voltage relationship (Gss-Vj) was a bell-shaped curve that could be adequately described by a two-state Boltzmann equation with a minimum Gj of 0.32-0.34, a half-inactivation voltage of -69 and +61 mV and an effective valence of 2.4-2.8. Recordings of gap junction channel currents (ij) yielded linear ij-Vj relationships with slope conductances of approximately 20-30 and 45-50 pS. A kinetic model, based on the Boltzmann relationship and the polarity reversal data, suggests that the opening (alpha) and closing (beta) rate constants have nearly identical voltage sensitivities with a Vo of +/- 62 mV. The data presented in this study are not consistent with the contingent gating scheme (for two identical gates in series) proposed for other more Vj-dependent gap junctions and alternatively suggest that each gate responds to the applied Vj independently of the state (open or closed) of the other gate.
众多双细胞电压钳研究得出结论，哺乳动物心脏间隙连接的电导不受跨连接电压（Vj）分布的调节，尽管据报道新生大鼠心室肌细胞低电导对之间的间隙连接通道表现出Vj依赖性行为。在本研究中，使用双全细胞膜片钳技术在配对的3日龄新生仓鼠心室肌细胞中定量检测了宏观间隙连接电导（gj）对跨连接电压的依赖性。用针对大鼠连接蛋白43（根据其cDNA序列预测的一种43-kD间隙连接蛋白）氨基酸252 - 271的位点特异性抗血清进行免疫定位，特异性地标记了培养的肌细胞之间的接触区域。在整个检测的电压范围内（0≤Vj≤±100 mV），新生仓鼠肌细胞对的瞬时电流 - 电压（Ij - Vj）关系呈线性。然而，对于Vj大于±50 mV时，稳态Ij - Vj关系是非线性的。失活和恢复过程均遵循单指数时间进程（tau失活 = 100 - 1000 ms，tau恢复约等于300 ms）。然而，Ij在极性反转时迅速恢复。归一化的稳态连接电导 - 电压关系（Gss - Vj）是一条钟形曲线，可用双态玻尔兹曼方程充分描述，最小Gj为0.32 - 0.34，半失活电压为 - 69和 + 61 mV，有效价为2.4 - 2.8。间隙连接通道电流（ij）的记录产生线性ij - Vj关系，斜率电导约为20 - 30和45 - 50 pS。基于玻尔兹曼关系和极性反转数据的动力学模型表明，开放（α）和关闭（β）速率常数具有几乎相同的电压敏感性，Vo为±62 mV。本研究中呈现的数据与为其他更多Vj依赖性间隙连接提出的偶然门控方案（用于串联的两个相同门）不一致，相反表明每个门独立于另一个门的状态（开放或关闭）对施加的Vj作出反应。
