Valentijn J A, Louiset E, Vaudry H, Cazin L
European Institute for Peptide Research, C.N.R.S. URA 650, UA I.N.S.E.R.M., University of Rouen, Mont-Saint-Aignan, France.
Brain Res. 1991 Sep 27;560(1-2):175-80. doi: 10.1016/0006-8993(91)91229-t.
The firing patterns of cultured frog melanotrophs were studied using the patch-clamp technique. In the cell-attached mode, unitary currents were frequently observed as well as biphasic waveforms which were attributed to action potentials 'leaking' through the patch membrane. An inwardly rectifying single-unit current was observed with pipette solutions containing either 100 mM K+ or 100 mM Na+. Under both conditions, these channels displayed an identical I/V relationship, yielding a unitary conductance of 110 pS. The channel opening time was extremely long (50-3000 ms) and single-channel currents showed typical relaxations, which triggered bursts of action currents. In the whole-cell configuration large (2-12 mV) fluctuations in the membrane voltage of current-clamped cells frequently occurred. The deflections appeared to result from single-channel currents. Depolarizing 'events' often led to the discharge of action potentials. Taken together, our data provide evidence for the existence of high-conductance cationic channels in frog pars intermedia cells. These channels may, at least in some cases, be responsible for the generation of pacemaker depolarizations, thereby regulating firing behaviour. It is concluded, that the current traversing a single channel can seriously affect the membrane potential and excitability of frog melanotrophs.
运用膜片钳技术研究了培养的青蛙促黑素细胞的放电模式。在细胞贴附模式下，经常观察到单位电流以及双相波形，这归因于动作电位通过膜片膜“泄漏”。在含有100 mM K⁺ 或100 mM Na⁺ 的微管溶液中观察到内向整流单单位电流。在这两种情况下，这些通道呈现相同的电流-电压关系，产生110 pS的单位电导。通道开放时间极长（50 - 3000毫秒），单通道电流呈现典型的弛豫，引发动作电流爆发。在全细胞配置中，钳制电流的细胞的膜电压经常出现大的（2 - 12毫伏）波动。这些偏转似乎是由单通道电流引起的。去极化“事件”常常导致动作电位的发放。综上所述，我们的数据为青蛙中间叶细胞中高电导阳离子通道的存在提供了证据。这些通道至少在某些情况下可能负责起搏器去极化的产生，从而调节放电行为。得出的结论是，通过单个通道的电流会严重影响青蛙促黑素细胞的膜电位和兴奋性。
