Maruyama Y, Petersen O H
J Membr Biol. 1984;81(1):83-7. doi: 10.1007/BF01868812.
The Ca2+-activated nonselective cation channel in mouse pancreatic acini has been studied with the help of patch-clamp single-channel current recording in both the cell-attached conformation and in excised inside-out membrane patches. In intact resting mouse pancreatic acinar cells no unitary activity was observed. Adding saponin to the bath solution to disrupt the plasma membrane (apart from the isolated patch membrane from which current recording was made) evoked unitary inward current steps when the free ionized Ca2+ concentration in the bath ([Ca2+]i) was 5 X 10(-8) M or above. When an electrically isolated patch membrane was excised and the internal aspects of the plasma membrane were exposed to the bath solution, channel activation could be obtained when [Ca2+]i was 10(-7) M or above. However, with the passage of time the total inward current declined and about 1 min after excision no unitary current steps could be observed. At this stage Ca2+ in micromolar concentration was needed to open the channels and several hundred micromoles of Ca2+ per liter were required for maximal channel activation. Our results indicate that the Ca2+ -activated nonselective cation channel is more sensitive to internal Ca2+ than hitherto understood and that it may therefore play a role under physiological conditions in intact cells.
借助膜片钳单通道电流记录技术，在细胞贴附模式和切除的内向外膜片模式下，对小鼠胰腺腺泡中的钙离子激活非选择性阳离子通道进行了研究。在完整的静息小鼠胰腺腺泡细胞中，未观察到单一通道活性。向浴液中添加皂角苷以破坏质膜（除了进行电流记录的分离膜片），当浴液中游离钙离子浓度（[Ca2+]i）为5×10(-8) M或更高时，会诱发单一内向电流阶跃。当切除电隔离的膜片并将质膜内部暴露于浴液时，当[Ca2+]i为10(-7) M或更高时可获得通道激活。然而，随着时间的推移，总内向电流下降，切除后约1分钟，未观察到单一电流阶跃。在此阶段，需要微摩尔浓度的钙离子来打开通道，每升需要数百微摩尔的钙离子才能实现最大通道激活。我们的结果表明，钙离子激活非选择性阳离子通道对内部钙离子的敏感性比迄今所理解的更高，因此它可能在完整细胞的生理条件下起作用。
