Hatch M, Freel R W
Department of Zoology and Physiology, Louisiana State University, Baton Rouge 70803.
Pflugers Arch. 1988 Mar;411(3):333-8. doi: 10.1007/BF00585124.
Electrolyte transport across rabbit caecal epithelium was investigated in vitro using conventional short-circuiting and radioisotope techniques. In standard saline the caecum exhibited a relatively high short-circuit current (Isc = 4.4 microEq.cm-2.h-1) and conductance (6.43 mS.cm-2). Both sodium and chloride were absorbed (JNa(net) = 6.40 and JCl(net) = 3.40 microEq.cm-2.h-1) and potassium was secreted (JK(net) = -0.5 microEq.cm-2.h-1). Removal of Na+ abolished Isc and JCl(net) whereas removal of Cl- reduced JNa(net) to 2.92 microEq.cm-2.h-1 but did not alter Isc. In HCO3(-)-free salines containing 10(-4) M acetazolamide JCl(net) was abolished and JNa(net) and Isc were reduced to 2.3 and 2.5 microEq.cm-2.h-1 respectively. A positive residual ion flux (approximately 1 microEq.cm-2.h-1) was detected in standard and Cl(-)-free salines but not in Na+-free or HCO3- buffers. Mucosal amiloride (10(-3) M) decreased net Na+ and Cl- absorption but did not decrease Isc. Mucosal DIDS (10(-4) M) decreased JCl(net) while mucosal bumetanide (10(-4) M) did not affect any of the measured parameters. Finally, addition of theophylline (8 mM) stimulated Cl- secretion and increased Isc. It is concluded that net sodium absorption by caecal epithelia occurs by both electrogenic and electroneutral mechanisms whereas net chloride absorption occurs only by an electroneutral process. Coupling of the absorptive fluxes of Na+ and Cl- may result from Na+/H+ and Cl-/HCO3- antiport systems in this tissue. Finally, it is proposed that up to half of the Isc is due to a Na+-dependent secretion of bicarbonate ion.
采用传统的短路法和放射性同位素技术，对兔盲肠上皮的电解质转运进行了体外研究。在标准盐溶液中，盲肠呈现出相对较高的短路电流（Isc = 4.4微当量·厘米⁻²·小时⁻¹）和电导（6.43毫西门子·厘米⁻²）。钠和氯均被吸收（JNa(净) = 6.40，JCl(净) = 3.40微当量·厘米⁻²·小时⁻¹），钾则被分泌（JK(净) = -0.5微当量·厘米⁻²·小时⁻¹）。去除Na⁺可消除Isc和JCl(净)，而去除Cl⁻可使JNa(净)降至2.92微当量·厘米⁻²·小时⁻¹，但不改变Isc。在含有10⁻⁴ M乙酰唑胺的无HCO₃⁻盐溶液中，JCl(净)被消除，JNa(净)和Isc分别降至2.3和2.5微当量·厘米⁻²·小时⁻¹。在标准和无Cl⁻盐溶液中检测到正的残余离子通量（约1微当量·厘米⁻²·小时⁻¹），但在无Na⁺或HCO₃⁻缓冲液中未检测到。黏膜施加氨氯地平（10⁻³ M）可降低Na⁺和Cl⁻的净吸收，但不降低Isc。黏膜施加二苯乙烯二磺酸（DIDS，10⁻⁴ M）可降低JCl(净)，而黏膜施加布美他尼（10⁻⁴ M）对任何测量参数均无影响。最后，添加茶碱（8 mM）可刺激Cl⁻分泌并增加Isc。得出的结论是，盲肠上皮的钠净吸收通过电生成和电中性机制发生，而氯净吸收仅通过电中性过程发生。Na⁺和Cl⁻吸收通量的偶联可能源于该组织中的Na⁺/H⁺和Cl⁻/HCO₃⁻反向转运系统。最后，有人提出高达一半的Isc是由于碳酸氢根离子的Na⁺依赖性分泌所致。
