A novel sustained inward current activated at the diastolic pacemaker potential

为了阐明离子电流与细胞体积变化之间的关系，在膜片钳实验中，使用光学装置测量了豚鼠心室肌细胞的细胞宽度。将等渗浴液切换为50、70、150和200%渗透溶液时，细胞宽度分别为对照的121.1(]SY.+- [)3.3% （n=4）、110.8(]SY.+- [)2.2% （n=27）、87.1(]SY.+- [)1.8% （n=6）、82.6(]SY.+- [)1.1% （n=6）。在70%低渗溶液中应用300 nM异丙肾上腺素（Iso）可使细胞宽度从111.2(]SY.+- .[)1.4%减小到106.2(]SY.+- . [)1.8%, （n=13）。在等渗诱导的体积减小之后，回到等渗溶液诱导的细胞宽度减小到低于对照水平（94.8(]SY.+- .[)1.6%）。Iso在等渗溶液中的应用也使细胞宽度降低到96.5(]SY.+- [)1.3% (n=8)，同时伴随着2-4 mV的膜去极化。在其他5个细胞中，未观察到等诱导的体积减小和膜去极化。在全细胞电压钳断条件下，Iso激活了向内Cl<@D1-@>D1电流，降低了细胞宽度。如果通过移动保持电位和施加200 muM pinacidil诱导大的向外或向内K<@D1+@>D1电流，则细胞宽度分别减小或增加。在gramicidin穿孔全细胞箝位条件下，即使诱导较大的向内K<@D1+@>D1电流，细胞宽度也没有变化。当使用微移液管将测试溶液的应用限制在延长的肌细胞的一半时，暴露于低渗或高渗测试溶液的部分细胞宽度分别增加或减少。而其余肌细胞的反应方向相反。通过离子通道的连续离子通量可以引起细胞体积的变化。

To clarify the relationship between the ionic current flow and the cell volume change, the cell width was measured using an optic device during patch clamp experiments in guinea-pig ventricular myocytes. On switching the isotonic bath solution to 50,70,150 and 200% osmotic solutions, the cell width changed to 121.1(]SY.+-。[)3.3% (n=4), 110.8(]SY.+-。[)2.2% (n=27), 87.1(]SY.+-。[)1.8% (n=6), 82.6(]SY.+-。[)1.1% (n=6) of control, respectively. The applicaation of 300 nM isoprenaline (Iso) in the 70% hypotonic solution induced a decrease of the cell width from 111.2(]SY.+-。[)1.4% to 106.2(]SY.+-。[)1.8%, (n=13). Following the Iso-induced volume decrease, returning to the isotonic solution induced a decrease of the cell width below the control level (94.8(]SY.+-。[)1.6%). The application of Iso in the isotonic solution also decreased the cell width to 96.5(]SY.+-。[)1.3% (n=8) control, accompanied by a membrane depolarization of 2-4 mV.In other 5 cells neither Iso-induced volume decrease nor membrane depolarization was observed. Under the ruptured whole-cell voltage clamp condition, Iso activated the inward Cl<@D1-@>D1 current and decreased the cell width. If a large outward or inward K<@D1+@>D1 current was induced by shifting the holding potential and by applying 200 muM pinacidil, the cell width decreased or increased, respectively. Under the gramicidin-perforated whole-cell clamp condition, the cell width did not change even when a large inward K<@D1+@>D1 current was induced. When the application of test solution was limited to a half of the elongated myocyte by using a micro-pipette, the cell width increased or decreased in the part exposed to the hypotonic or hypertonic test solutions, respectively. While the rest part of the myocyte responded in the opposite direction. It is concluded that a continuous ionic flux through ion channels is capable of inducing cell volume change.