Marty A, Tan Y P, Trautmann A
J Physiol. 1984 Dec;357:293-325. doi: 10.1113/jphysiol.1984.sp015501.
Isolated cells from rat lacrimal glands were studied with patch-clamp techniques. Whole-cell and cell-attached recordings were obtained while the cells were stimulated by application of carbamylcholine or of the Ca ionophore, A23187. The results were compared with recordings of Ca-dependent channels obtained in isolated patches. Whole-cell recordings revealed two types of carbamylcholine-induced current. At low levels of stimulation, a specific class of Ca-dependent K channels was selectively activated ('BK channels'). With more intense stimulation an inward current, Ii, was obtained at the cell resting potential. Ii rose rather abruptly after a long delay. In several cells, Ii currents presented spontaneous oscillations. Both K and Ii current responses to carbamylcholine were due to activation of muscarinic receptors. Both responses were elicited by a rise of the intracellular Ca concentration. The immediate source of Ca was intracellular. Replacement of intracellular K with either Na or Cs blocked BK channels entirely, thus allowing the study of Ii currents free from K currents. Ii responses to carbamylcholine were, however, less frequently obtained in Na- or Cs-dialysed cells than in K-dialysed cells. In symmetrical NaCl solutions, Ii inverted at 0 mV. When replacing part of the intracellular or extracellular Cl with glutamate the reversal potential, Ei, was found to vary in the same direction as the equilibrium potential for Cl ions, ECl. In some experiments, Ei was close to ECl but in others Ei deviated strongly from ECl. These experiments suggested that Ii was mainly due to a Cl-selective conductance, and that another conductance type was contributing to Ii in variable proportions. It was found that, in K-free solutions, Ii had a reversal potential very close to ECl. Noise analysis showed that the Cl channels involved in Ii current had a unit conductance of about 1-2 pS in symmetrical NaCl solutions. At -60 mV, the mean channel open time derived from noise power spectra was about 200 ms. The activation of the Ca-dependent Cl channels was increased by depolarization. Voltage jumps elicited slow exponential relaxations. At -60 mV, the time constants of the relaxations were in the range 100-250 ms. Cell-attached recordings suggested that internal Ca activated three types of channel, depending on the Ca concentration: BK channels, 2-4 pS channels and 25 pS channels. Inside-out and outside-out patch conditions allowed a rough estimate to be made of the Ca concentration needed to activate each class of channel.(ABSTRACT TRUNCATED AT 400 WORDS)
采用膜片钳技术对大鼠泪腺分离细胞进行了研究。在应用氨甲酰胆碱或钙离子载体A23187刺激细胞时，获得了全细胞和细胞贴附记录。将结果与在分离膜片中获得的钙依赖性通道记录进行了比较。全细胞记录揭示了两种氨甲酰胆碱诱导的电流。在低刺激水平下，一类特定的钙依赖性钾通道被选择性激活（“大电导钾通道”）。随着刺激强度增加，在细胞静息电位处获得内向电流Ii。Ii在长时间延迟后突然上升。在几个细胞中，Ii电流呈现自发振荡。钾电流和Ii电流对氨甲酰胆碱的反应均归因于毒蕈碱受体的激活。两种反应均由细胞内钙浓度升高引起。钙的直接来源是细胞内。用钠或铯替代细胞内钾完全阻断了大电导钾通道，从而使得能够在无钾电流干扰的情况下研究Ii电流。然而，与钾透析细胞相比，在钠或铯透析细胞中，对氨甲酰胆碱的Ii反应较少见。在对称的氯化钠溶液中，Ii在0 mV处反转。当用谷氨酸替代部分细胞内或细胞外氯时，发现反转电位Ei与氯离子平衡电位ECl的变化方向相同。在一些实验中，Ei接近ECl，但在另一些实验中，Ei与ECl有很大偏差。这些实验表明，Ii主要归因于氯选择性电导，并且另一种电导类型以可变比例对Ii有贡献。发现在无钾溶液中，Ii的反转电位非常接近ECl。噪声分析表明，参与Ii电流的氯通道在对称氯化钠溶液中的单位电导约为1 - 2 pS。在-60 mV时，由噪声功率谱得出的平均通道开放时间约为200 ms。钙依赖性氯通道的激活因去极化而增强。电压阶跃引发缓慢的指数松弛。在-60 mV时，松弛的时间常数在100 - 250 ms范围内。细胞贴附记录表明，细胞内钙根据钙浓度激活三种类型的通道：大电导钾通道、2 - 4 pS通道和25 pS通道。内面向外和外面向内的膜片钳条件使得能够对激活每类通道所需的钙浓度进行粗略估计。（摘要截选至400字）
