Lucas W J
Department of Botany, University of California, Davis, California 95616.
Plant Physiol. 1978 Apr;61(4):487-93. doi: 10.1104/pp.61.4.487.
The effect of 10 mm K(+) on the HCO(3) (-) influx in Chara corallina has been used to distinguish a Ca(2+)-dependent membrane integrity site from the HCO(3) (-) transport site which is also Ca(2+)-dependent (Lucas and Dainty, Plant Physiology 1977 60: 862-867).In the presence of 0.2 mm Ca(2+) at pH 9, 10 mm K(+) inhibits the HCO(3) (-) influx and depolarizes the membrane potential. Inhibition of the HCO(3) (-) influx may be prevented by raising the Ca(2+) concentration in the solution or by addition of Mg(2+), Sr(2+), or Mn(2+). Protection is also afforded by 20 mm Na(+) and Cs(+) but not by Rb(+) which acts as a weak analog of K(+) in producing inhibition of the HCO(3) (-) influx and depolarization of the membrane potential. With the exception of Na(+), ions which prevent inhibition of the influx also prevent depolarization of the membrane potential.Once inhibited by 10 mm K(+), HCO(3) (-) transport cannot be restored by addition of Ca(2+), Mg(2+), or Sr(2+) in less than 3 hours. Addition of Mn(2+), however, results in a progressive restoration of the proportion of cells with influxes equal to the control value. Mn(2+) also produces an increase in the membrane potential with a sharp hyperpolarization occurring at a threshold of about-180 mv. This sudden recovery of the HCO(3) (-) influx in individual cells contrasts with the gradual recovery observed when the K(+) concentration is reduced to 0.2 mm. Since Mn(2+) cannot substitute for Ca(2+) at the HCO(3) (-) transport site, restoration of HCO(3) (-) transport by Mn(2+) involving the membrane integrity site, as evidenced by the effect on the membrane potential and resistance, is clearly separate. The other divalent cations were able to restore HCO(3) (-) transport if applied at a concentration of 2 mm for 14 hours.The OH(-) efflux is also inhibited by 10 mm KCl. It is postulated that voltage dependency of the OH(-) or HCO(3) (-) transport systems may account for the observed effects of 10 mm K(+) on the HCO(3) (-) influx.
利用10毫米钾离子对珊瑚轮藻中碳酸氢根离子内流的影响，将依赖钙离子的膜完整性位点与同样依赖钙离子的碳酸氢根离子转运位点区分开来（卢卡斯和丹蒂，《植物生理学》1977年第60卷：862 - 867页）。在pH值为9且存在0.2毫米钙离子的情况下，10毫米钾离子会抑制碳酸氢根离子内流并使膜电位去极化。通过提高溶液中的钙离子浓度或添加镁离子、锶离子或锰离子，可以防止对碳酸氢根离子内流的抑制。20毫米钠离子和铯离子也能起到保护作用，但铷离子不能，铷离子在抑制碳酸氢根离子内流和使膜电位去极化方面，作用类似于较弱的钾离子。除了钠离子外，能防止内流抑制的离子也能防止膜电位去极化。一旦被10毫米钾离子抑制，在少于3小时内，添加钙离子、镁离子或锶离子都无法恢复碳酸氢根离子的转运。然而，添加锰离子会使内流与对照值相等的细胞比例逐渐恢复。锰离子还会使膜电位升高，在约 - 180毫伏的阈值处会出现急剧的超极化。单个细胞中碳酸氢根离子内流的这种突然恢复，与将钾离子浓度降至0.2毫米时观察到的逐渐恢复形成对比。由于锰离子在碳酸氢根离子转运位点不能替代钙离子，锰离子对碳酸氢根离子转运的恢复涉及膜完整性位点，这从其对膜电位和电阻的影响可以看出，二者显然是分开的。如果以2毫米的浓度施加14小时，其他二价阳离子能够恢复碳酸氢根离子转运。氢氧根离子外流也会被10毫米氯化钾抑制。据推测，氢氧根离子或碳酸氢根离子转运系统的电压依赖性可能解释了观察到的10毫米钾离子对碳酸氢根离子内流的影响。
