Höller H, Breves G, Kocabatmaz M, Gerdes H
Department of Physiology, School of Veterinary Medicine, Hannover, F.R.G.
Q J Exp Physiol. 1988 Jul;73(4):609-18. doi: 10.1113/expphysiol.1988.sp003180.
Experiments were carried out in vivo and in vitro to study the flux of Ca2+ across the sheep rumen wall. Buffer solutions with five different Ca2+ concentrations in the range 0.2-3.6 mmol l-1 were introduced into the isolated, emptied and washed reticulo-rumen for 1 h to determine Ca2+ net flux. Phosphate concentrations were either kept constant at 8 mmol l-1, or varied so as to maintain a constant phosphate/Ca2+ ratio of 2:1. Under both conditions there was a Ca2+ net secretion into the rumen at Ca2+ concentrations below approximately 1 mmol l-1 whereas Ca2+ net absorption occurred at higher Ca2+ concentrations and linearly increased with increasing Ca2+ concentrations. When phosphate concentrations were reduced to 4.3 and 0.6 mmol l-1 (Ca2+, 3 mmol l-1) Ca2+ net absorption was reduced by about 50% and completely abolished, respectively. The unidirectional (mucosal-to-serosal or serosal-to-mucosal) Ca fluxes in vitro, JCams and JCasm, were measured in Ussing chambers with computer-controlled voltage clamp. Under short-circuit current conditions (Ca2+ and phosphate, 2 mmol l-1) there was a significant net flux of Ca2+ from the mucosal to the serosal side. This net flux of Ca2+ was abolished when ouabain was added to the serosal solution, indicating that the unidirectional Ca2+ flux JCams and, hence, the net flux of Ca2+ was dependent upon active Na+ transport accomplished by the Na, K-ATPase system. Under voltage clamp conditions, the net flux of Ca2+ was greatly increased at a potential difference PD = -25 mV (serosa negative) but disappeared at PD = +25 mV (serosa positive). Analysis of the unidirectional Ca2+ fluxes JCams and JCasm under varying potential differences indicated that both Ca2+ fluxes consisted of a PD-dependent and a PD-independent component. The results show that the reticulo-rumen participates in Ca2+ absorption in sheep.
进行了体内和体外实验，以研究钙离子（Ca2+）跨绵羊瘤胃壁的通量。将含有五种不同Ca2+浓度（范围为0.2 - 3.6 mmol l-1）的缓冲溶液引入分离、排空并冲洗过的网瘤胃中1小时，以测定Ca2+净通量。磷酸盐浓度要么保持在8 mmol l-1恒定，要么变化以维持2:1的恒定磷酸盐/Ca2+比值。在这两种条件下，当Ca2+浓度低于约1 mmol l-1时，有Ca2+净分泌到瘤胃中，而在较高Ca2+浓度下发生Ca2+净吸收，并且随着Ca2+浓度的增加呈线性增加。当磷酸盐浓度降至4.3和0.6 mmol l-1（Ca2+为3 mmol l-1）时，Ca2+净吸收分别减少约50%和完全消除。在具有计算机控制电压钳的尤斯灌流室中测量体外单向（黏膜到浆膜或浆膜到黏膜）Ca通量，即JCams和JCasm。在短路电流条件下（Ca2+和磷酸盐为2 mmol l-1），有显著的Ca2+从黏膜侧向浆膜侧的净通量。当在浆膜溶液中加入哇巴因时，这种Ca2+净通量被消除，表明单向Ca2+通量JCams以及因此的Ca2+净通量依赖于由钠钾ATP酶系统完成的主动钠转运。在电压钳条件下，当电位差PD = -25 mV（浆膜为负）时，Ca2+净通量大大增加，但在PD = +25 mV（浆膜为正）时消失。对不同电位差下单向Ca2+通量JCams和JCasm的分析表明，两种Ca2+通量都由电位差依赖性和电位差非依赖性成分组成。结果表明，网瘤胃参与绵羊的Ca2+吸收。
