Gusev G P, Sherstobitov A O
Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St. Petersburg, Russia.
Gen Physiol Biophys. 1996 Apr;15(2):129-43.
Na+ transport across the lamprey erythrocyte membrane was examined using 22Na as a tracer. Both Na+ influx and Na+ effux exhibit a wide variability among different lampreys due to amiloride-sensitive components. Addition of 1 mmol/l amiloride to incubation media resulted in a decrease of the Na+ influx from 8.4 +/- 0.9 to 5.5 +/- 0.3 mmol/l cells/h (n = 18, P < 0.001), and of the rate coefficient of the Na+ efflux from 0.50 +/- 0.08 to 0.18 +/- 0.02 h-1 (n = 20, P < 0.001). Cell shrinkage induced by addition of 100 mmol/l sucrose to an isotonic medium was associated with a significant increase in both the Na+ influx and the Na+ efflux which was entirely blocked by amiloride. The amiloride-sensitive components of the Na+ fluxes were abolished by cell swelling in hypotonic media (210 mosm/kg water). In addition to activation of Na+ influx by isoproterenol reported earlier (Gusev et al. 1992b), the present study demonstrated that isoproterenol also stimulated Na+ efflux from the lamprey erythrocytes. Exposure of the red cells to an Na(+)-free medium (replacing with NMDG+) resulted in a significant enhancement in Na+ efflux (approximately 3-fold) which was completely inhibited by amiloride. Incubation of the red cells in an unbuffered saline was accompanied by a gradual raising of external pHe measured with a pH-sensitive electrode, and the addition of 100 mmol/l sucrose to isotonic medium had no effect on pHe. The amiloride-sensitive component of the Na+ influx in the red cells incubated in the isotonic medium was unchanged when pHe was lowered from 7.4 to 6.5 but it disappeared after raising pHe to 8.0. The results of this study show that the lamprey erythrocyte membrane exhibits an amiloride-sensitive transport in either direction which is activated by cell shrinkage and isoproterenol, and is attenuated by cell swelling. No evidence was obtained for the contribution of well known Na(+)-H+ and Na(+)-Na+ exchangers to this amiloride-sensitive pathway under the conditions of our experiments.
使用²²Na作为示踪剂研究了七鳃鳗红细胞膜上的Na⁺转运。由于存在amiloride敏感成分，不同七鳃鳗之间的Na⁺内流和Na⁺外流均表现出很大的变异性。向孵育培养基中添加1 mmol/l amiloride会导致Na⁺内流从8.4±0.9降至5.5±0.3 mmol/（l细胞·h）（n = 18，P < 0.001），以及Na⁺外流速率系数从0.50±0.08降至0.18±0.02 h⁻¹（n = 20，P < 0.001）。向等渗培养基中添加100 mmol/l蔗糖诱导的细胞收缩与Na⁺内流和Na⁺外流的显著增加相关，而这种增加完全被amiloride阻断。在低渗培养基（210 mosm/kg水）中细胞肿胀会消除Na⁺通量的amiloride敏感成分。除了早期报道的异丙肾上腺素对Na⁺内流的激活作用（Gusev等人，1992b）外，本研究还表明异丙肾上腺素也刺激七鳃鳗红细胞的Na⁺外流。将红细胞暴露于无Na⁺培养基（用NMDG⁺替代）会导致Na⁺外流显著增强（约3倍），而这种增强被amiloride完全抑制。在无缓冲盐溶液中孵育红细胞会伴随着用pH敏感电极测量的细胞外pH值逐渐升高，并且向等渗培养基中添加100 mmol/l蔗糖对pH值没有影响。当pH值从7.4降至6.5时，等渗培养基中孵育的红细胞中Na⁺内流的amiloride敏感成分不变，但当pH值升至8.0后该成分消失。本研究结果表明，七鳃鳗红细胞膜在两个方向上均表现出amiloride敏感转运，这种转运由细胞收缩和异丙肾上腺素激活，并因细胞肿胀而减弱。在我们的实验条件下，没有证据表明已知的Na⁺-H⁺和Na⁺-Na⁺交换体对这种amiloride敏感途径有贡献。
