Lamb F S, Volk K A, Shibata E F
Department of Physiology and Biophysics, University of Iowa College of Medicine, Iowa City 52242.
Circ Res. 1994 Oct;75(4):742-50. doi: 10.1161/01.res.75.4.742.
Whole-cell patch-clamp techniques were used to study enzymatically dispersed epicardial coronary artery smooth muscle cells. Depolarizing voltage pulses of 500-millisecond duration from -60 mV (118 mmol/L CsCl, 22 mmol/L tetraethylammonium chloride, and 5 mmol/L EGTA pipette solution) elicited inward L-type calcium currents (ICa). When EGTA was omitted from the pipette solution, an outward current was superimposed on the calcium current, and repolarizing voltage steps produced an inward tail current (IT). The amplitude of these inward currents was proportional to the ICa amplitude from -30 to +50 mV. The time course of decay of the current was well fit by a single exponential equation. The time constant (tau) of this equation did not change with the size of IT but was clearly voltage dependent (shorter at more negative potentials). Changing the chloride reversal potential from -1.3 to -39.7 mV by anion substitution using methanesulfonate as the chloride replacement in the pipette solution shifted the zero current level of IT from 0.9 +/- 0.56 to -33.1 +/- 0.85 mV. The tail current was blocked by nifedipine (10(-6) mol/L) and by isosmolar calcium substitution with barium in the bath solution and was enhanced by the dihydropyridine agonist Bay K 8644 (10(-6) mol/L). IT was also blocked by the chloride channel blockers DIDS (10(-4) mol/L) and niflumic acid (10(-5) mol/L). Caffeine (10(-2) mol/L), which releases intracellular calcium stores, caused an inward current at holding potentials (-60 mV), which was inhibited by DIDS. Caffeine also inhibited subsequent attempts to elicit IT by depolarizing pulses (88% reduction in IT).(ABSTRACT TRUNCATED AT 250 WORDS)
采用全细胞膜片钳技术研究酶解分散的心外膜冠状动脉平滑肌细胞。从 -60 mV（移液管溶液含118 mmol/L氯化铯、22 mmol/L四乙铵氯化物和5 mmol/L乙二醇双四乙酸）施加持续500毫秒的去极化电压脉冲，引发内向L型钙电流（ICa）。当移液管溶液中省略乙二醇双四乙酸时，外向电流叠加在钙电流上，复极化电压阶跃产生内向尾电流（IT）。这些内向电流的幅度在 -30至 +50 mV范围内与ICa幅度成比例。电流衰减的时间过程可用单指数方程很好地拟合。该方程的时间常数（tau）不随IT大小变化，但明显依赖电压（在更负电位时更短）。通过在移液管溶液中用甲磺酸盐替代氯化物进行阴离子置换，将氯反转电位从 -1.3 mV改变为 -39.7 mV，使IT的零电流水平从0.9±0.56 mV移至 -33.1±0.85 mV。尾电流被硝苯地平（10⁻⁶ mol/L）以及浴液中用钡进行等渗钙置换所阻断，并被二氢吡啶激动剂Bay K 8644（10⁻⁶ mol/L）增强。IT也被氯通道阻滞剂4,4'-二异硫氰酸根合芪-2,2'-二磺酸（DIDS，10⁻⁴ mol/L）和氟硝丁酰胺（10⁻⁵ mol/L）阻断。咖啡因（10⁻² mol/L）释放细胞内钙储存，在钳制电位（-60 mV）时引起内向电流，该电流被DIDS抑制。咖啡因还抑制随后通过去极化脉冲引发IT的尝试（IT减少88%）。（摘要截断于250字）
