Deitmer J W
J Physiol. 1984 Oct;355:137-59. doi: 10.1113/jphysiol.1984.sp015411.
Action potentials and voltage-dependent membrane currents have been investigated in the fresh-water hypotrich ciliate Stylonychia mytilus, using two intracellular micro-electrodes. The inward current-voltage (Iin-V) relationship has two maxima, the first around -45 mV, and the second around -17 mV (resting and holding membrane potential being -50 mV). The shape of the Iin-V relationship is virtually unaltered in the presence of the K-channel blockers tetraethylammonium, 4-aminopyridine or internal Cs. The inward currents exhibit a differential sensitivity to both external CO and Cd; the inward current activated at potentials greater than or equal to -40 mV is more sensitive to these divalent cations than the inward current activated at around -45 mV. This suggests the presence of two different types of Ca inward currents. Both types of inward currents are present when Ca is replaced by Ba (or Sr). The small inward current recorded between -48 and -40 mV relaxes similarly in Ca and in Ba solutions. The larger inward current, recorded at -30 or -20 mV, relaxes rapidly in Ca solution but only slowly and incompletely in Ba solution. A two-pulse protocol revealed that for both types of inward currents inactivation may depend partially upon the influx and/or intracellular accumulation of the charge-carrying divalent cation. There appears to be a significant difference in the degree of inactivation of the two types of inward currents, however, when Ba is the charge carrier. When the cell spontaneously released, or was induced to release its membranellar band (row of compound cilia), the second, "all-or-none' component of the action potential, and the maximum of the Iin-V relationship at -45 mV disappeared. The first, graded peak of the action potential and the larger maximum of the Iin-V relationship remained essentially unaltered. The smaller Ca current and the action potential shoulder also disappeared when the anterior half of the cell (with most of the membranellar band) was severed, but not when the posterior half was cut off. When recording from a membranellar band vesicle both types of inward currents were present. The results suggest that the two components of the action potential may correspond to the two types of Ca currents. These Ca currents are separable by their localization in the membrane. The smaller Ca current appears to be restricted to the membranellar band.(ABSTRACT TRUNCATED AT 400 WORDS)
利用两个细胞内微电极，对淡水腹毛目纤毛虫贻贝棘尾虫的动作电位和电压依赖性膜电流进行了研究。内向电流-电压（Iin-V）关系有两个最大值，第一个在-45 mV左右，第二个在-17 mV左右（静息和钳制膜电位为-50 mV）。在存在钾通道阻滞剂四乙铵、4-氨基吡啶或内部铯的情况下，Iin-V关系的形状几乎没有改变。内向电流对外部一氧化碳和镉表现出不同的敏感性；在大于或等于-40 mV的电位下激活的内向电流比在-45 mV左右激活的内向电流对这些二价阳离子更敏感。这表明存在两种不同类型的钙内向电流。当钙被钡（或锶）取代时，两种类型的内向电流都存在。在-48至-40 mV之间记录到的小内向电流在钙溶液和钡溶液中的松弛情况相似。在-30或-20 mV记录到的较大内向电流在钙溶液中迅速松弛，但在钡溶液中仅缓慢且不完全松弛。双脉冲实验表明，对于两种类型的内向电流，失活可能部分取决于携带电荷的二价阳离子的内流和/或细胞内积累。然而，当钡是电荷载体时，两种类型的内向电流的失活程度似乎存在显著差异。当细胞自发释放或被诱导释放其膜带（一排复合纤毛）时，动作电位的第二个“全或无”成分以及Iin-V关系在-45 mV处的最大值消失。动作电位的第一个分级峰值和Iin-V关系的较大最大值基本保持不变。当细胞的前半部分（带有大部分膜带）被切断时，较小的钙电流和动作电位肩部也消失了，但后半部分被切断时则没有。当从膜带囊泡进行记录时，两种类型的内向电流都存在。结果表明，动作电位的两个成分可能对应于两种类型的钙电流。这些钙电流可以通过它们在膜中的定位来区分。较小的钙电流似乎局限于膜带。（摘要截短于400字）
