Schwartz M, Schilb T P, Carrasquer G
Department of Physics, University of Louisville, KY 40292, USA.
Can J Physiol Pharmacol. 1996 Jan;74(1):58-64.
Previously, it was found that a decrease in nutrient (serosal) Na+ decreased the transmucosal potential difference (PD) in the secreting and inhibited states of fundi of stomachs of Rana pipiens. This PD response, designated as anomalous, was explained by two different models, an electrogenic NaCl symport and an electrogenic NaHCO3 symport. To test these hypotheses, experiments were done at pH approximately 7.4 in which the PD response to a change in nutrient Na+ was compared in 25, 5, and 0 mM nutrient HCO3- solutions. In the H+ secreting state, all HCO3- concentrations gave, for a 10-fold decrease in nutrient Na+, about the same PD response (9-12 mV). The PD response was 8.5, 2.9, and 0 mV higher in the inhibited state for 25, 5, and 0 mM HCO3- , respectively. Experiments with decreasing nutrient Cl- decreased the anomalous PD response to Na+ changes, and the response became insignificant at Cl- concentrations of 20 mM or less in the secreting state. The anomalous PD response to a decrease in Na+ concentration was obtained for all Cl- concentrations (0-79 mM), becoming less with decreasing Cl- in the inhibited state. These results support a NaCl symport to explain the PD response in the secreting state and a NaHCO3 symport to explain the enhancement in the inhibited state.
先前发现，在牛蛙胃底的分泌和抑制状态下，营养物质（浆膜）中Na⁺的减少会降低跨粘膜电位差（PD）。这种被称为异常的PD反应由两种不同的模型解释，即电中性NaCl同向转运体和电中性NaHCO₃同向转运体。为了验证这些假设，在pH约为7.4的条件下进行了实验，比较了在25 mM、5 mM和0 mM营养HCO₃⁻溶液中，PD对营养物质Na⁺变化的反应。在H⁺分泌状态下，对于营养物质Na⁺降低10倍的情况，所有HCO₃⁻浓度下的PD反应大致相同（9 - 12 mV）。在抑制状态下，25 mM、5 mM和0 mM HCO₃⁻时的PD反应分别比分泌状态高8.5 mV、2.9 mV和0 mV。降低营养物质Cl⁻的实验降低了对Na⁺变化的异常PD反应，在分泌状态下，当Cl⁻浓度为20 mM或更低时，反应变得不明显。对于所有Cl⁻浓度（0 - 79 mM），都观察到了对Na⁺浓度降低的异常PD反应，在抑制状态下，随着Cl⁻浓度降低反应减弱。这些结果支持用NaCl同向转运体来解释分泌状态下的PD反应，用NaHCO₃同向转运体来解释抑制状态下的增强反应。
