Kuijpers G A, De Pont J J, Westerhoff H V
Laboratory of Cell Biology and Genetics, NIDDK, Bethesda, MD.
Biochim Biophys Acta. 1989 Aug 21;984(1):71-80. doi: 10.1016/0005-2736(89)90344-1.
Fluid secretion by the isolated rabbit pancreas is strongly dependent on the presence of Na+ in the bathing medium. Substitution of Na+ by another cation such as Li+ or K+ causes an inhibition of fluid secretion rate and a change in the composition of the secreted fluid which is dependent on the nature of the substituent cation. Stimulation of the pancreas by CCK-8 or carbachol increases paracellular ion permeability and, in some cases, also fluid secretion rate. We present a simple, quantitative model for ion and water secretion which accounts for the effects observed upon Na+ substitution and stimulation. The main features are active, Na+-dependent transcellular HCO3- transport and passive, paracellular cation and anion permeation. The activity of the HCO3- pump is dependent on the energy status of the cell and on the Na+ concentration in the bathing medium, and is competitively inhibited by K+. The paracellular ion permeabilities can be modulated by stimulatory agonists. We examine the extent to which, according to the model, fluid secretion is controlled by the various system parameters such as ion permeabilities and ion pump activity, and by external parameters such as the ion concentrations in the bathing medium. In addition, calculation of the effects of changes in these parameters are carried out in order to gain more insight in the mechanisms of secretion.
离体兔胰腺的液体分泌强烈依赖于浴液中Na⁺的存在。用Li⁺或K⁺等其他阳离子取代Na⁺会导致液体分泌速率受到抑制，以及分泌液成分发生变化，这种变化取决于取代阳离子的性质。用CCK - 8或卡巴胆碱刺激胰腺会增加细胞旁离子通透性，在某些情况下还会增加液体分泌速率。我们提出了一个简单的离子和水分泌定量模型，该模型解释了在Na⁺取代和刺激时观察到的效应。主要特征是主动的、依赖Na⁺的跨细胞HCO₃⁻转运以及被动的细胞旁阳离子和阴离子通透。HCO₃⁻泵的活性取决于细胞的能量状态和浴液中的Na⁺浓度，并受到K⁺的竞争性抑制。细胞旁离子通透性可由刺激激动剂调节。我们根据该模型研究了液体分泌在多大程度上受各种系统参数（如离子通透性和离子泵活性）以及外部参数（如浴液中的离子浓度）的控制。此外，还对这些参数变化的影响进行了计算，以便更深入地了解分泌机制。
