小腸および大腸上皮細胞における電解質の輸送

抄録

One of the most important functions of small and large intestines is the electrolyte transport under both the physiological and pathological (e.g. diarrhoeal) conditions. Ion absorption or secretion takes place along or against its electrochemical potential gradient through the transcellular and paracellular pathways. Transcellular ion transport should involve uphill transport against the electrochemical potential gradient either at the brushborder cell membrane (BBM) or at the basolateral cell membrane (BLM). Carrier-mediated cotransport (symport) and exchange transport (antiport) play essential roles in such uphill transport processes. The Na⁺-CI^-symport (as well as Na⁺-sugar or-amino acid symport), Na⁺/H⁺antiport and ATPase-dependent Na⁺/K⁺ antiport (Na⁺/K⁺ exchange pump) participate in the NaCl absorption in villus epithelial cells and in the NaCl secretion in crypt epithelial cells. The Cl^-/HCO₃-and Na⁺/ H⁺ antiporters are involved in the intestinal HCO₃-secretion and absorption. It is suggested that both the Ca²⁺ channel at BBM and the ATPase-dependent Na⁺/Ca²⁺ antiport (Na⁺/Ca²⁺ exchange pump) at BLM are essentially implicated in the active Ca²⁺ absorption in the intestinal epithelia.