Role of de novo protein synthesis and calmodulin in rapid activation of Na(+)‐H+ exchange of 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 (pHi). Since this activation is rapid (within 30 min), it may be mediated by either a genomic or non‐genomic pathway. 2. pHi was measured in single microperfused early distal tubule segments using the fluorescent probe 2',7'‐bis(carboxyethyl)‐5,6‐carboxyfluorescein (BCECF). 3. A 30 min incubation in aldosterone increased both resting pHi and the setpoint of the Na(+‐H+ exchanger. These changes were prevented by the mineralocorticoid receptor antagonist, spironolactone. 4. Actinomycin D and cycloheximide, inhibitors of transcription and translation, respectively, were without effect on resting pHi, but inhibited activation of the Na(+)‐H+ exchanger by aldosterone. 5. The effect of aldosterone upon pHi and setpoint was also prevented by the calcium‐calmodulin antagonist, W‐7. 6. These results indicate that, although the response to aldosterone is rapid, aldosterone binds to a specific mineralocorticoid receptor which then triggers gene activation followed by de novo protein synthesis. Furthermore, since calmodulin is a known activator of the Na(+)‐H+ exchanger, and the response is inhibited by W‐7, it is suggested that this protein may be calmodulin.