Ahearn G A, Hadley N F
Am J Physiol. 1977 Nov;233(5):R198-207. doi: 10.1152/ajpregu.1977.233.5.R198.
Water transport in desert scorpion ileum involves two independent transfer pathways operating in parallel: 1) paracellular flow occurs through intercellular spaces in response to transmural osmotic or ionic gradients; and 2) transcellular water transport occurs across apical and basal cell membranes in response to a basal, energy-requiring sodium efflux process. The tissue exhibits no osmotic rectification over the range of transepithelial osmotic gradients imposed (Lp = hydraulic conductivity), Lp = 95 x 10(-7) cm - s-1 - atm-1), but displays apparent asymmetric ion permeability in response to transmural ion gradients, as determined by codiffusional water movements across the preparation. Osmotic permeability ((Pos), Pos = 1.13 x 10(-3) cm - s-1) of the tissue exceeds diffusional permeability ((Pd), Pd = 1.45 x 10(-5) cm - s-1) by almost two orders of magnitude. In the absence of osmotic or hydrostatic pressure gradients, transmural water transport requires cellular metabolism, is sodium-dependent, is inhibited by potassium, and produces an apparent strongly hypotonic absorbate. This water transport process appears to be adaptive, as scorpion dehydration results in alterations of luminal ion concentrations that favor increased net flow of water to the hemolymph.
1）细胞旁流动通过细胞间间隙发生，以响应跨壁渗透或离子梯度；2）跨细胞水运输通过顶端和基底细胞膜发生，以响应基底的、需要能量的钠外流过程。在所施加的跨上皮渗透梯度范围内（Lp = 水力传导率，Lp = 95×10⁻⁷ cm·s⁻¹·atm⁻¹），该组织未表现出渗透整流，但根据跨制剂的共扩散水运动测定，其对跨壁离子梯度表现出明显的不对称离子通透性。该组织的渗透通透性（（Pos），Pos = 1.13×10⁻³ cm·s⁻¹）比扩散通透性（（Pd），Pd = 1.45×10⁻⁵ cm·s⁻¹）高出近两个数量级。在没有渗透或静水压力梯度的情况下，跨壁水运输需要细胞代谢，依赖于钠，受钾抑制，并产生明显的强低渗吸收液。这种水运输过程似乎具有适应性，因为蝎子脱水会导致管腔离子浓度的改变，有利于增加水向血淋巴的净流量。
