Nilsson B O, Gomez M, Santiago Carrilho R, Nordström I, Hellstrand P
Department of Physiology and Biophysics, University of Lund, Sweden.
Acta Physiol Scand. 1995 Jul;154(3):355-65. doi: 10.1111/j.1748-1716.1995.tb09919.x.
Effects of the naturally occurring polyamine spermine on electrical and contractile properties of the rat portal vein were studied. 1 mM spermine nearly abolished spike activity and spontaneous contractions and decreased the intracellular Ca2+ concentration ([Ca2+]i). The phasic force responses to 0.1 and 1 microM phenylephrine were partially inhibited, but not the sustain plateau contraction caused by 5 microM phenylephrine. The Ca(2+)-force relation in high-K+ (128 mM)-depolarized veins was shifted to the right, EC50 for Ca2+ increasing from 0.50 +/- 0.03 mM (control, n = 8) to 0.65 +/- 0.06 and to 0.94 +/- 0.03 at 1 (n = 4) and 10 (n = 3) mM spermine, respectively. However, at a Ca2+ concentration of 2.5 mM, giving maximal force, there was no effect of spermine (1 mM) on either force or [Ca2+]i. Whereas extracellular spermine thus reduced contractile activity at moderate levels of stimulation, increased intracellular concentration of spermine potentiated the force response to Ca2+. Intracellular loading of spermine by reversible permeabilization increased its concentration by 2-3 times. The spontaneous activity and response to phenylephrine were unchanged. However, the Ca(2+)-force relation of depolarized veins was shifted to the left, EC50 decreasing from 0.51 +/- 0.04 mM in controls (n = 7) to 0.36 +/- 0.02 mM in the loaded veins (n = 9). Spermine increased Ca(2+)-activated force in portal veins permeabilized with beta-escin. The degree of potentiation was consistent with observed effects in spermine-loaded intact veins. The results suggest that spermine at physiological intracellular concentration may contribute to the determination of Ca2+ sensitivity in vascular smooth muscle cells.
研究了天然存在的多胺精胺对大鼠门静脉电特性和收缩特性的影响。1 mM精胺几乎消除了峰电位活动和自发收缩，并降低了细胞内Ca2+浓度（[Ca2+]i）。对0.1和1 microM去氧肾上腺素的相性力反应受到部分抑制，但对5 microM去氧肾上腺素引起的持续性平台收缩没有抑制作用。在高K+（128 mM）去极化的静脉中，Ca(2+)-力关系向右移动，Ca2+的EC50从0.50±0.03 mM（对照组，n = 8）分别增加到1 mM精胺时的0.65±0.06 mM（n = 4）和10 mM精胺时的0.94±0.03 mM（n = 3）。然而，在Ca2+浓度为2.5 mM时产生最大力，1 mM精胺对力或[Ca2+]i均无影响。因此，细胞外精胺在中等刺激水平下降低了收缩活性，而细胞内精胺浓度增加则增强了对Ca2+的力反应。通过可逆通透化进行细胞内精胺加载使其浓度增加了2 - 3倍。自发活动和对去氧肾上腺素的反应未改变。然而，去极化静脉的Ca(2+)-力关系向左移动，EC50从对照组的0.51±0.04 mM（n = 7）降低到加载静脉中的0.36±0.02 mM（n = 9）。精胺增加了用β-七叶皂苷通透化的门静脉中Ca(2+)-激活的力。增强程度与在精胺加载的完整静脉中观察到的效应一致。结果表明，生理细胞内浓度的精胺可能有助于确定血管平滑肌细胞中Ca2+的敏感性。
