Wegener J W, Nawrath H
Pharmakologisches Institut der Universität Mainz, Germany.
Naunyn Schmiedebergs Arch Pharmacol. 1996 Dec;354(6):746-54. doi: 10.1007/BF00166901.
The effects of the phenylalkylamines verapamil (V), gallopamil (G), and devapamil (D) and their corresponding quaternary derivatives on the transient outward current (Ito) were examined in rat ventricular cardiomyocytes using the whole-cell patch-clamp technique. The question was addressed, whether phenylalkylamines act on Ito from the inside or the outside or from both sides of the cell membrane. To this end, the myocytes were either superfused extracellularly or perfused intracellularly with drug-containing solutions. In addition, the effects of verapamil were investigated at different pH-values. V, G, and D (30 microM each), applied extracellularly, reduced the steady state current of Ito, Ito(150 ms), to 34 +/- 3.3, 33 +/- 6, and 30 +/- 5, respectively (% of control; means +/- SEM). The effects of V (30 microM) on Ito were similar at various external pH-values (reduction of Ito(150 ms) by 69 +/- 6 at pH 6.5, by 66 +/- 4 at pH 7.4, by 68 +/- 8 at pH 8.5, and by 58 +/- 10 at pH 9.5; % of control; means +/- SEM). In contrast, the effect of 4-aminopyridine (300 microM) on Ito was enhanced after alkalinisation: the peak current of Ito was reduced to 49 +/- 5 at pH 7.4 and to 5 +/- 2 at pH 9.2 (% of control; means +/- SEM). V, G, and D (300 microM) failed to produce any effect on Ito, when applied intracellularly (values of Ito(150 ms): 97 +/- 6, 105 +/- 4, and 94 +/- 4, respectively; % of control; means +/- SEM). In contrast, 4-aminopyridine (3 mM) depressed the peak current of Ito to 69 +/- 6% of control (mean +/- SEM), when applied intracellularly. The permanently charged quaternary derivatives of the phenylalkylamines q-V, q-G, and q-D (300 microM) did not significantly affect Ito, when applied extracellularly (values of Ito(150 ms): 94 +/- 2, 90 +/- 3, and 94 +/- 3, respectively; % of control; means +/- SEM) but diminished Ito, when applied intracellularly (reduction of Ito(150 ms) to 43 +/- 5, 56 +/- 7, and 63 +/- 4, respectively; % of control; means +/- SEM). Intracellularly applied V (300 microM) did not reduce Ito at pH 6.5 at which V is protonated to 99.4%. It is suggested that tertiary phenylalkylamines act on Ito by binding to a membrane site accessible from the outside, whereas their quaternary derivatives affect Ito by binding to a membrane site located at the inside of the cell membrane. In contrast, 4-aminopyridine is supposed to act on Ito from the inside of the cell membrane.
采用全细胞膜片钳技术，在大鼠心室肌细胞中研究了苯烷基胺类药物维拉帕米（V）、加洛帕米（G）和地伐帕米（D）及其相应的季铵衍生物对瞬时外向电流（Ito）的影响。研究的问题是，苯烷基胺类药物是从细胞膜内侧、外侧还是两侧作用于Ito。为此，将含有药物的溶液分别对心肌细胞进行细胞外灌流或细胞内灌注。此外，还研究了不同pH值下维拉帕米的作用。细胞外施加V、G和D（各30 μM）时，Ito的稳态电流Ito(150 ms)分别降至34±3.3%、33±6%和30±5%（对照百分比；平均值±标准误）。在不同的细胞外pH值下，V（30 μM）对Ito的作用相似（pH 6.5时Ito(150 ms)降低69±6%，pH 7.4时降低66±4%，pH 8.5时降低68±8%，pH 9.5时降低58±10%；对照百分比；平均值±标准误）。相比之下，碱化后4-氨基吡啶（300 μM）对Ito的作用增强：pH 7.4时Ito的峰值电流降至49±5%，pH 9.2时降至5±2%（对照百分比；平均值±标准误）。细胞内施加V、G和D（300 μM）时，对Ito无任何影响（Ito(150 ms)的值分别为97±6%、105±4%和94±
