Basolateral Mg2+/Na+ exchange regulates apical nonselective cation channel in sheep rumen epithelium via cytosolic Mg2+.
Basolateral Mg2+/Na+ exchange regulates apical nonselective cation channel in sheep rumen epithelium via cytosolic Mg2+.
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基底外侧 Mg2/Na 交换通过胞质 Mg2 调节绵羊瘤胃上皮的顶端非选择性阳离子通道。
DOI：
10.1152/ajpgi.00275.2004
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发表时间：
2005
期刊：
影响因子：
--
通讯作者：
H. Martens
中科院分区：
文献类型：
--
作者：
S. Leonhard;F. Stumpff;I. Brinkmann;G. Breves;H. Martens
高钾日粮导致反刍动物钠和镁吸收的反向调节，表明存在某种形式的串扰。先前的Ussing室实验已经证明了瘤胃上皮细胞顶膜中的二价敏感Na（+）电导。用膜片钳法观察了瘤胃上皮细胞的二价敏感性、非选择性阳离子电导（NSCC），其K（+）通透性> Cs（+）通透性> Na（+）通透性。当Mg（2+）或Ca（2+）和Mg（2+）从内部或外部溶液或两者中去除时，电导增加，整流降低。Ba（2+）对电导有明显的阻断作用，而TEA对电导无明显的阻断作用。随后，我们研究了这种电导测量的短路电流（I（SC））在尤辛室。已知毛喉素、IBMX和茶碱在二价阳离子存在下阻断I（sc）和Na跨瘤胃上皮的转运。当通过去除粘膜钙来刺激NSCC时，I（SC）的初始降低随后是随后的增加。cAMP介导的I（sc）增加可被低血清钠（+）和血清丙咪嗪或血清阿米洛利的加入所减少，并取决于粘膜镁的可用性。腔内阿米洛利没有效果。通量研究表明，低血清Na（+）减少（28）镁流量从粘膜到血清。数据表明，cAMP刺激基底外侧Na（+）/Mg（2+）交换，减少胞质Mg。这增加了通过顶端膜中的镁敏感性NSCC的钠摄取。同样地，在高钾饲料摄入后镁吸收的减少可能促进钠的吸收，如在瘤胃代谢调节的研究中所观察到的。可能，草手足抽搐（低镁血症）是这种有用机制的副作用。
High potassium diets lead to an inverse regulation of sodium and magnesium absorption in ruminants, suggesting some form of cross talk. Previous Ussing chamber experiments have demonstrated a divalent sensitive Na(+) conductance in the apical membrane of ruminal epithelium. Using patch-clamped ruminal epithelial cells, we could observe a divalent sensitive, nonselective cation conductance (NSCC) with K(+) permeability > Cs(+) permeability > Na(+) permeability. Conductance increased and rectification decreased when either Mg(2+) or both Ca(2+) and Mg(2+) were removed from the internal or external solution or both. The conductance could be blocked by Ba(2+), but not by tetraethylammonium (TEA). Subsequently, we studied this conductance measured as short-circuit current (I(sc)) in Ussing chambers. Forskolin, IBMX, and theophylline are known to block both I(sc) and Na transport across ruminal epithelium in the presence of divalent cations. When the NSCC was stimulated by removing mucosal calcium, an initial decrease in I(sc) was followed by a subsequent increase. The cAMP-mediated increase in I(sc) was reduced by low serosal Na(+) and serosal addition of imipramine or serosal amiloride and depended on the availability of mucosal magnesium. Luminal amiloride had no effect. Flux studies showed that low serosal Na(+) reduced (28)Mg fluxes from mucosal to serosal. The data suggest that cAMP stimulates basolateral Na(+)/Mg(2+) exchange, reducing cytosolic Mg. This increases sodium uptake through a magnesium-sensitive NSCC in the apical membrane. Likewise, the reduction in magnesium uptake that follows ingestion of high potassium fodder may facilitate sodium absorption, as observed in studies of ruminal osmoregulation. Possibly, grass tetany (hypomagnesemia) is a side effect of this useful mechanism.
影响因子：
3.9
作者：
Fatholahi, M;LaNoue, K;Scarpa, A
通讯作者：
Scarpa, A