ROLE OF DE-NOVO PROTEIN-SYNTHESIS AND CALMODULIN IN RAPID ACTIVATION OF NA-H+ EXCHANGE BY ALDOSTERONE IN FROG DILUTING SEGMENT()

1. In the amphibian early distal tubule aldosterone activates the Na+- H+ exchangers, resulting in an increase in intracellular pH (pH(i)). S ince this activation is rapid (within 30 min), it may be mediated by e ither a genomic or non-genomic pathway. 2. pH(i) was measured in singl e microperfused early distal tubule segments using the fluorescent pro be 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein (BCECF). 3. A 30 min incubation in aldosterone increased both resting pH(i) and the setpoi nt of the Na+-H+ exchanger. These changes were prevented by the minera locorticoid receptor antagonist, spironolactone. 4. Actinomycin D and cycloheximide, inhibitors of transcription and translation, respective ly, were without effect on resting pH(i), but inhibited activation of the Na+-H+ exchanger by aldosterone. 5. The effect of aldosterone upon pH(i) and setpoint was also prevented by the calcium-calmodulin antag onist, W-7. 6. These results indicate that, although the response to a ldosterone is rapid, aldosterone binds to a specific mineralocorticoid receptor which then triggers gene activation followed by de novo prot ein synthesis. Furthermore, since calmodulin is a known activator of t he Na+-H+ exchanger, and the response is inhibited by W-7, it is sugge sted that this protein may be calmodulin.