title: Vasopressin regulates apical and basolateral Na(+)-H+ antiporters in mouse medullary thick ascending limbs.
abstract: We assessed in isolated perfused mouse medullary thick ascending limb (MTAL) segments Na(+)-H+ antiporter activity in both apical and basolateral membranes and the effects of arginine vasopressin (AVP) on the activities of these antiporters under isotonic conditions using 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein to monitor intracellular pH (pHi). When the apical Na(+)-H+ antiporter was inhibited in the absence of AVP with removal of luminal Na+ plus addition of 0.5 mM amiloride, a small but significant increase in pHi was observed after luminal NH4Cl-induced acidification of MTAL cells to pHi less than 6.7. This increase in pHi was dependent on basolateral Na+ and inhibited with 0.5 mM basolateral amiloride, consistent with the function of a basolateral Na(+)-H+ antiporter. Basolateral AVP (100 microU/ml) enhanced the rate of pHi recovery due to the basolateral Na(+)-H+ antiporter by more than twofold. In contrast, AVP decreased the apical Na(+)-H+ antiporter activity by 50%. In the absence of AVP, addition of 0.5 mM amiloride to the luminal perfusate reduced steady-state pHi by 0.40 +/- 0.07 units, whereas exposure of the basolateral membrane to the same concentration of amiloride had no effect on pHi (delta pHi = 0.01 +/- 0.01 units). AVP reduced the magnitude of cell acidification on exposure of apical membranes to amiloride (delta pHi = 0.16 +/- 0.03) but increased the pHi response to basolateral amiloride (delta pHi = 0.09 +/- 0.00). Thus Na(+)-H+ antiporters are present on both apical and basolateral membranes of the mouse MTAL in the absence of AVP. AVP stimulates the basolateral, while inhibiting the apical, Na(+)-H+ antiporter.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Harvard Center for the Study of Kidney Disease, Harvard Medical School, Boston, Massachusetts.
authors.forename: A M
authors.initials: AM
authors.lastname: Sun
authors.forename: D
authors.initials: D
authors.lastname: Kikeri
authors.forename: S C
authors.initials: SC
authors.lastname: Hebert
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001127:Arginine Vasopressin / Q000494:pharmacology / Q000502:physiology*; D002352:Carrier Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D006859:Hydrogen / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007679:Kidney Medulla; D008138:Loop of Henle / Q000378:metabolism* / Q000648:ultrastructure; D051379:Mice; D012964:Sodium / Q000502:physiology; D017923:Sodium-Hydrogen Exchangers
chemical_list: D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; D001127:Arginine Vasopressin; D000584:Amiloride; D006859:Hydrogen; D012964:Sodium