Na+/H(+)-exchange in A6 cells: polarity and vasopressin regulation.
We have analyzed the mechanism of Na(+)-dependent pHi recovery from an acid load in A6 cells (an amphibian distal nephron cell line) by using the intracellular pH indicator 2'7'-bis(2-carboxyethyl)5,6 carboxyfluorescein (BCECF) and single cell microspectrofluorometry. A6 cells were found to express Na+/H(+)-exchange activity only on the basolateral membrane: Na+/H(+)-exchange activity follows simple saturation kinetics with an apparent Km for Na+ of approximately 11 mM; it is inhibited in a competitive manner by ethylisopropylamiloride (EIPA). This Na+/H(+)-exchange activity is inhibited by pharmacological activation of protein kinase A (PKA) as well as of protein kinase C (PKC). Addition of arginine vasopressin (AVP) either at low (subnanomolar) or at high (micromolar) concentrations inhibits Na+/H(+)-exchange activity; AVP stimulates IP3 production at low concentrations, whereas much higher concentrations are required to stimulate cAMP formation. These findings suggest that in A6 cells (i) Na+/H(+)-exchange is located in the basolateral membrane and (ii) PKC activation (heralded by IP3 turnover) is likely to be the mediator of AVP action at low AVP concentrations.
Casavola
V
V
Department of Physiology, University of Zürich, Switzerland.
Guerra
L
L
Helmle-Kolb
C
C
Reshkin
S J
SJ
Murer
H
H
D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000663:Amphibians; D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology; D001127:Arginine Vasopressin / Q000494:pharmacology / Q000502:physiology*; D002352:Carrier Proteins / Q000502:physiology*; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000032:analysis / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004789:Enzyme Activation / Q000187:drug effects; D006863:Hydrogen-Ion Concentration; D015544:Inositol 1,4,5-Trisphosphate / Q000032:analysis / Q000378:metabolism; D009399:Nephrons / Q000166:cytology* / Q000378:metabolism / Q000502:physiology; D011493:Protein Kinase C / Q000502:physiology; D011494:Protein Kinases / Q000502:physiology; D012964:Sodium / Q000494:pharmacology; D017923:Sodium-Hydrogen Exchangers
D000889:Anti-Arrhythmia Agents; D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; D001127:Arginine Vasopressin; D000584:Amiloride; D015544:Inositol 1,4,5-Trisphosphate; D012964:Sodium; D000242:Cyclic AMP; D011494:Protein Kinases; D011493:Protein Kinase C; C039614:ethylisopropylamiloride