Cremaschi D, Meyer G, Rossetti C, Bottà G, Palestini P
J Membr Biol. 1987;95(3):209-18. doi: 10.1007/BF01869483.
Cl- influx at the luminal border of the epithelium of rabbit gallbladder was measured by 45-sec exposures to 36Cl- and 3H-sucrose (as extracellular marker). Its paracellular component was evaluated by the use of 25 mM SCN- which immediately and completely inhibits Cl- entry into the cell. Cellular influx was equal to 16.7 mu eq cm-2 hr-1 and decreased to 8.5 mu eq cm-2 hr-1 upon removal of HCO3- from the bathing media and by bubbling 100% O2 for 45 min. When HCO3- was present, cellular influx was again about halved by the action of 10(-4) M acetazolamide, 10(-5) to 10(-4) M furosemide, 10(-5) to 10(-4) M 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonate (SITS), 10(-3) M amiloride. The effects of furosemide and SITS were tested at different concentrations of the inhibitor and with different exposure times: they were maximal at the concentrations reported above and nonadditive. In turn, the effects of amiloride and SITS were not additive. Acetazolamide reached its maximal action after an exposure of about 2 min. When exogenous HCO3- was absent, the residual cellular influx was insensitive to acetazolamide, furosemide and SITS. When exogenous HCO3- was present in the salines, Na+ removal from the mucosal side caused a slow decline of cellular Cl- influx; conversely, it immediately abolished cellular Cl- influx in the absence of HCO3-. In conclusion, about 50% of cellular influx is sensitive to HCO3-, inhibitable by SCN-, acetazolamide, furosemide, SITS and amiloride and furthermore slowly dependent on Na+. The residual cellular influx is insensitive to bicarbonate, inhibitable by SCN-, resistant to acetazolamide, furosemide, SITS and amiloride, and immediately dependent on Na+. Thus, about 50% of apical membrane NaCl influx appears to result from a Na+/H+ and Cl-/HCO3- exchange, whereas the residual influx seems to be due to Na+-Cl- cotransport on a single carrier. Whether both components are simultaneously present or the latter represents a cellular homeostatic counter-reaction to the inhibition of the former is not clear.
通过将兔胆囊上皮细胞腔面边界暴露于³⁶Cl⁻和³H - 蔗糖（作为细胞外标志物）45秒来测量Cl⁻内流。通过使用25 mM SCN⁻评估其细胞旁成分，该物质可立即完全抑制Cl⁻进入细胞。细胞内流等于16.7 μeq cm⁻² hr⁻¹，当从浴液中去除HCO₃⁻并通入100% O₂ 45分钟后，细胞内流降至8.5 μeq cm⁻² hr⁻¹。当存在HCO₃⁻时，10⁻⁴ M乙酰唑胺、10⁻⁵至10⁻⁴ M呋塞米、10⁻⁵至10⁻⁴ M 4 - 乙酰氨基 - 4'-异硫氰基芪 - 2,2'-二磺酸盐（SITS）、10⁻³ M阿米洛利的作用可使细胞内流再次减半。在不同抑制剂浓度和不同暴露时间下测试了呋塞米和SITS的作用：它们在上述浓度下作用最大且无相加作用。同样，阿米洛利和SITS的作用也无相加性。乙酰唑胺在暴露约2分钟后达到最大作用。当不存在外源性HCO₃⁻时，残余的细胞内流对乙酰唑胺、呋塞米和SITS不敏感。当盐溶液中存在外源性HCO₃⁻时，从黏膜侧去除Na⁺会导致细胞Cl⁻内流缓慢下降；相反，在不存在HCO₃⁻时，它会立即消除细胞Cl⁻内流。总之，约50%的细胞内流对HCO₃⁻敏感，可被SCN⁻、乙酰唑胺、呋塞米、SITS和阿米洛利抑制，并且还缓慢依赖于Na⁺。残余的细胞内流对碳酸氢盐不敏感，可被SCN⁻抑制，对乙酰唑胺、呋塞米、SITS和阿米洛利有抗性，并且立即依赖于Na⁺。因此，约50%的顶端膜NaCl内流似乎是由Na⁺/H⁺和Cl⁻/HCO₃⁻交换引起的，而残余内流似乎是由于单一载体上的Na⁺ - Cl⁻共转运。尚不清楚这两种成分是否同时存在，或者后者是否代表细胞对前者抑制的一种稳态反应。
