Saïag B, Milon D, Bentue-Ferrer D, Allain H, Rault B, Van den Driessche J
Laboratoire de Physiologie, U.F.R. de Pharmacie, Rennes, France.
Res Commun Chem Pathol Pharmacol. 1994 Mar;83(3):255-69.
Contractile responses to norepinephrine (noradrenaline, NE 10(-5) M) in the canine saphenous vein (SV) are significantly, although slightly, reduced (14%) when induced in a physiological medium depleted of calcium for 1 hour (+ EGTA). In contrast, they are inhibited by about 75% after 24 hr in calcium free physiological saline solution (P.S.S.). ED50 of norepinephrine in 1-hr calcium-free medium and in normal Ca++ P.S.S. are 6 x 10(-7)M and 4.2 x 10(-7)M, respectively. Two blockers of extracellular calcium entry have also been cited as inhibitors of intracellular calcium pool refilling. At concentrations of 10(-6)M, 10(-5)M and 10(-4)M, diltiazem and nicardipine inhibit the norepinephrine-induced contractions (NIC) in a concentration-dependent manner. At 10(-4)M, the two calcium blockers inhibit the NIC by 70% and by 72% respectively in Ca++ free (+ EGTA) P.S.S. Nifedipine and verapamil only begin to significantly inhibit NIC in Ca++ free (+ EGTA) P.S.S. at concentrations equal to or greater than 10(-5)M. At 10(-4)M concentration, control inhibition in Ca++ free P.S.S. was observed as 60% and 49%, respectively. Contrary to the other 3 calcium antagonists tested, diltiazem antagonises NIC significantly less in calcium-containing medium (45%) than in calcium-free medium (72%). Procaine at a concentration of 10(-3)M, described as sufficient to totally inhibit calcium release from its intracellular storage sites, only inhibits NIC by 52% in calcium free (+ EGTA) P.S.S. These results are consistent with the following conclusion: i) in the canine saphenous vein (SV), NIC is mainly mediated by calcium mobilization from its intracellular storage sites; ii) the calcium antagonists tested here and procaine are unable to totally inhibit, even at high concentrations, the contractions induced via intracellular calcium release; this characteristic is nonsignificant for nifedipine and verapamil at low concentrations (10(-6)M). iii) verapamil and nifedipine, like diltiazem and nicardipine at high concentrations, may not only possess the characteristics of extracellular calcium entry blockers, but also that of partial antagonist of NIC via non specific mechanisms; iv) diltiazem may relax the vascular smooth muscle of SV, not only by the above two properties, but also through another mechanism yet unknown; v) partial persistence of NIC on the SV under conditions of short or long extracellular calcium depletion may be due to a mechanism of intracellular Ca++ recycling, the smooth muscle cell partially retaining its intracellular Ca++.
在犬隐静脉（SV）中，当在不含钙的生理介质中诱导1小时（添加乙二醇双（2-氨基乙基醚）四乙酸（EGTA））时，对去甲肾上腺素（去甲肾上腺素，NE 10⁻⁵ M）的收缩反应虽有显著但轻微的降低（14%）。相比之下，在无钙生理盐溶液（P.S.S.）中放置24小时后，收缩反应受到约75%的抑制。在不含钙1小时的培养基和正常Ca²⁺ P.S.S.中，去甲肾上腺素的半数有效剂量（ED50）分别为6×10⁻⁷M和4.2×10⁻⁷M。两种细胞外钙内流阻滞剂也被认为是细胞内钙库再填充的抑制剂。在浓度为10⁻⁶M、10⁻⁵M和10⁻⁴M时，地尔硫䓬和尼卡地平以浓度依赖性方式抑制去甲肾上腺素诱导的收缩（NIC）。在10⁻⁴M时，这两种钙阻滞剂在不含钙（添加EGTA）的P.S.S.中分别抑制NIC 70%和72%。硝苯地平和维拉帕米仅在浓度等于或大于10⁻⁵M时才开始在不含钙（添加EGTA）的P.S.S.中显著抑制NIC。在10⁻⁴M浓度下，在不含钙的P.S.S.中观察到的对照抑制率分别为60%和49%。与其他3种测试的钙拮抗剂相反，地尔硫䓬在含钙培养基中对NIC的拮抗作用（45%）明显小于在无钙培养基中（72%）。浓度为10⁻³M的普鲁卡因被认为足以完全抑制钙从其细胞内储存位点的释放，但在不含钙（添加EGTA）的P.S.S.中仅抑制NIC 52%。这些结果与以下结论一致：i）在犬隐静脉（SV）中，NIC主要由细胞内储存位点的钙动员介导；ii）此处测试的钙拮抗剂和普鲁卡因即使在高浓度下也无法完全抑制通过细胞内钙释放诱导的收缩；对于低浓度（10⁻⁶M）的硝苯地平和维拉帕米，这一特性不显著。iii）维拉帕米和硝苯地平，与高浓度的地尔硫䓬和尼卡地平一样，可能不仅具有细胞外钙内流阻滞剂的特性，还具有通过非特异性机制对NIC的部分拮抗特性；iv）地尔硫䓬可能不仅通过上述两种特性，还通过另一种未知机制使SV的血管平滑肌松弛；v）在细胞外钙短期或长期耗竭的情况下，NIC在SV上的部分持续存在可能是由于细胞内Ca²⁺循环机制导致平滑肌细胞部分保留其细胞内Ca²⁺。
