Guan Y Y, Kwan C Y, Daniel E E
Smooth Muscle Research Program, McMaster University, Faculty of Health Sciences, Hamilton, Ont., Canada.
Can J Physiol Pharmacol. 1988 Aug;66(8):1053-6. doi: 10.1139/y88-172.
The effect of EGTA, commonly present in Ca2+-free physiological saline solution, on the contractile responses induced by Ca2+ and phenylephrine was studied in dog mesenteric arteries and aortas of rats and rabbits. EGTA substantially enhanced the contractile responses of these vascular strips or rings to added Ca2+ after a prolonged preincubation period in the Ca2+-free medium. The maximal level of the enhanced contractile responses was independent of EGTA concentration, but the rate of the maximal responses was faster at higher EGTA concentration, presumably as a result of faster removal of intracellular Ca2+. Such a Ca2+-induced response was sensitive to the Ca2+ antagonist, nifedipine. EGTA present at low concentrations (50 and 400 microM) in Ca2+-free medium also inhibited the phenylephrine-induced contractile response more prominently for the longer preincubation periods of the vascular tissues in Ca2+-free medium. Our results suggest that EGTA, even when added at low concentrations to the vascular smooth muscle for a sufficiently long period in Ca2+-free medium, may cause destabilization of the cell membranes leading to increased permeability to subsequently added Ca2+. EGTA may also remove the superficially bound Ca2+ and subsequently reduce the intracellular Ca2+ pool via extraction of the intracellular Ca2+ at the cell membrane surfaces.
在犬肠系膜动脉以及大鼠和家兔的主动脉中，研究了通常存在于无钙生理盐溶液中的乙二醇双四乙酸（EGTA）对钙离子（Ca2+）和去氧肾上腺素诱导的收缩反应的影响。在无钙培养基中经过长时间预孵育后，EGTA显著增强了这些血管条或血管环对添加的Ca2+的收缩反应。增强的收缩反应的最大水平与EGTA浓度无关，但在较高EGTA浓度下最大反应的速率更快，这可能是由于细胞内Ca2+去除更快的结果。这种Ca2+诱导的反应对Ca2+拮抗剂硝苯地平敏感。在无钙培养基中低浓度（50和400微摩尔）的EGTA，对于血管组织在无钙培养基中更长时间的预孵育，也更显著地抑制了去氧肾上腺素诱导的收缩反应。我们的结果表明，即使在无钙培养基中低浓度添加EGTA并在血管平滑肌中作用足够长的时间，也可能导致细胞膜不稳定，从而导致对随后添加的Ca2+的通透性增加。EGTA还可能去除表面结合的Ca2+，随后通过在细胞膜表面提取细胞内Ca2+来减少细胞内Ca2+池。
