title: Regulation of apical Na+ conductive transport in epithelia by pH.
abstract: Alterations in extracellular (pHo) and/or intracellular pH (pHi) have significant effects on the apical Na+ conductive transport in tight epithelia. They influence apical membrane Na+ conductance via a direct effect on amiloride-sensitive apical Na+ channel activity and indirectly through effects on the basolateral Na+/K(+)-ATPase. Changes in pH also modulate the hormonal regulation of apical Na+ conductive transport. The pH sensitive steps in hormone action include: (i) hormone-receptor binding, (ii) increase in intracellular cyclic 3',5'-adenosine monophosphate (cAMP), (iii) mobilization of intracellular free Ca2+ ([Ca2+]i), and (iv) incorporation of new channels into the apical membrane or recruitment of existing channels. Alternately, changes in pH induce secondary effects via alterations in [Ca2+]i. A reciprocal relationship between pHi and [Ca2+]i has been demonstrated in renal epithelial cells. Natriferic hormones induce a significant increase in pHi. There is a strong temporal relation between hormone-induced increase in pHi and overall increase in transepithelial Na+ transport. This suggests that changes in pHi act as an intermediate in the second messenger cascade initiated by the hormones. Several natriferic hormones activate Na(+)-H+ exchanger, H(+)-ATPase, H+/K(+)-ATPase, H+ conductive pathways in cell membranes or potential-induced changes in pHi. However, changes in pHi do not seem to be essential for the hormone effect on Na+ conductive transport. It is suggested that the role of pHi changes during hormone action is permissive rather than strictly obligatory.
authors.affiliation: Department of Physiology, Medical College of Virginia, Virginia Commonwealth University, Richmond, USA.
authors.forename: V
authors.initials: V
authors.lastname: Lyall
authors.forename: G M
authors.initials: GM
authors.lastname: Feldman
authors.forename: T U
authors.initials: TU
authors.lastname: Biber
mesh_terms: D000818:Animals; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism*; D004848:Epithelium / Q000378:metabolism; D006728:Hormones / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D015290:Second Messenger Systems; D012964:Sodium / Q000378:metabolism*
chemical_list: D006728:Hormones; D012964:Sodium