Chen J S, Walser M
Am J Physiol. 1977 Mar;232(3):F210-4. doi: 10.1152/ajprenal.1977.232.3.F210.
The conductance, ga, and electromotive force, E, of active ion transport across toad bladders mounted as sacs were estimated from electrical measurements made before and after addition of sufficient ouabain (1.89 X 10(-3) M) to eliminate spontaneous potential. The ratio of net sodium transport (estimated from bidirectional fluxes) to external current in bladders voltage clamped to 0 mV was significantly less than unity in a normal medium containing HCO3- and Cl- ions, and also when Cl- was replaced with SO42-. However, when acetazolamide was added or when HCO3- was replaced by phosphate, short-circuit current and net sodium transport became equal. Spontaneous potential, E, and ga were all reduced about 20% by these maneuvers. The response of bidirectional sodium fluxes to voltage clamping at 0 mV or 120 mV in a bicarbonate-free medium was otherwise similar to that observed in a normal medium: net flux varied linearly with potential and calculated fluxes in the active transport path indicated a value significantly greater than unity for the empirical constant Q in the equation for change in the flux ratio, f, with change in potential, psi, viz., delta ln f = Q(ZF/RT)delta psi, similar to the high value for this constant that we have found in a bicarbonate-containing medium. We conclude that bicarbonate ions facilitate active sodium transport and also may be actively transported from serosa to mucosa in Dominican toads. However, coupling between bicarbonate and sodium fluxes does not account for the high value for Q for sodium in the active transport path.
通过对蟾蜍膀胱制成的囊泡进行电测量，在添加足够的哇巴因（1.89×10⁻³ M）以消除自发电位前后进行测量，估算了跨囊泡的活性离子转运的电导（ga）和电动势（E）。在含有HCO₃⁻和Cl⁻离子的正常介质中，以及当Cl⁻被SO₄²⁻取代时，将膀胱电压钳制在0 mV时，净钠转运（根据双向通量估算）与外部电流的比值明显小于1。然而，当加入乙酰唑胺或用磷酸盐取代HCO₃⁻时，短路电流和净钠转运变得相等。这些操作使自发电位E和ga均降低了约20%。在无碳酸氢盐介质中，双向钠通量对0 mV或120 mV电压钳制的响应在其他方面与在正常介质中观察到的相似：净通量随电位呈线性变化，并且在活性转运途径中计算出的通量表明，通量比f随电位ψ变化的方程中经验常数Q的值明显大于1，即δln f = Q(ZF/RT)δψ，这与我们在含碳酸氢盐介质中发现的该常数的高值相似。我们得出结论，碳酸氢根离子促进活性钠转运，并且在多米尼加蟾蜍中也可能从浆膜向黏膜进行主动转运。然而，碳酸氢根和钠通量之间的偶联并不能解释活性转运途径中钠的Q值为何较高。
