Palmer L G
J Membr Biol. 1982;67(2):91-8. doi: 10.1007/BF01868651.
The ion selectivity of the apical membrane Na channel in the toad urinary bladder was investigated. The electrical potential difference and resistance across the basal-lateral membrane were reduced using high concentrations of KCl in the serosal bathing medium, and gradients for various ions were imposed across the apical membrane by altering the composition of the mucosal bathing medium. Ion fluxes through the channel were measured as the transepithelial current inhibited by amiloride, a specific blocker of the channel's Na conductance. The selectivity sequence for alkali metal cations was H greater than Li greater than Na much greater than K. K permeability was barely detectable; the selectivity for Na over K was about 1000:1. Ammonium, hydroxyl ammonium and hydrazinium ions were, like K, virtually impermeant. The results suggest that the size of the unhydrated ion is an important factor in determining permeability in this channel.
对蟾蜍膀胱顶端膜钠通道的离子选择性进行了研究。通过在浆膜侧浴液中使用高浓度氯化钾来降低跨基底外侧膜的电势差和电阻，并通过改变黏膜侧浴液的成分在顶端膜上施加各种离子的梯度。通过该通道的离子通量以被氨氯吡脒（该通道钠电导的特异性阻滞剂）抑制的跨上皮电流来测量。碱金属阳离子的选择性顺序为H＞Li＞Na＞＞K。钾的通透性几乎检测不到；钠对钾的选择性约为1000:1。铵离子、羟铵离子和肼离子与钾一样，几乎是不可通透的。结果表明，未水化离子的大小是决定该通道通透性的一个重要因素。
