Ammonia excretion via Rhcg1 facilitates Na+ uptake in larval zebrafish, Danio rerio, in acidic water
- Authors
- Kumai, Y., and Perry, S.F.
- ID
- ZDB-PUB-110816-8
- Date
- 2011
- Source
- American journal of physiology. Regulatory, integrative and comparative physiology 301(5): R1517-28 (Journal)
- Registered Authors
- Keywords
- rH protein, EIPA, Na+/H+ exchange, gene knockdown, ionic regulation
- MeSH Terms
-
- Amiloride/analogs & derivatives
- Amiloride/pharmacology
- Ammonia/metabolism*
- Animals
- Biological Transport
- Buffers
- Cation Transport Proteins/genetics
- Cation Transport Proteins/metabolism*
- Gene Knockdown Techniques
- Gills/drug effects
- Gills/embryology
- Gills/metabolism*
- Hydrogen-Ion Concentration
- Kinetics
- Larva/metabolism
- Macrolides/pharmacology
- Proton-Translocating ATPases/antagonists & inhibitors
- Proton-Translocating ATPases/metabolism
- Sodium/metabolism*
- Sodium-Hydrogen Exchangers/antagonists & inhibitors
- Sodium-Hydrogen Exchangers/genetics
- Sodium-Hydrogen Exchangers/metabolism
- Zebrafish
- Zebrafish Proteins/genetics
- Zebrafish Proteins/metabolism*
- PubMed
- 21832207 Full text @ Am. J. Physiol. Regul. Integr. Comp. Physiol.
The involvement of a Na+/H+ exchanger (NHE) in mediating Na+ uptake by freshwater (FW) fish is currently debated. Although supported indirectly by empirical molecular and pharmacological data, theoretically its operation should be constrained thermodynamically owing to unfavorable chemical gradients. Recently, there has been an increasing focus on ammonia channels (Rh proteins) as potentially contributing to Na+ uptake across the FW fish gill. In this study, we tested the hypothesis that Rhcg1, a specific apical isoform of Rh protein, is critically important in facilitating Na+ uptake in zebrafish larvae via its interaction with NHE. Treating larvae (4 day post fertilization; dpf) with 5-(N-ethyl-N-isopropyl amiloride (EIPA, an inhibitor of NHE), caused a significant reduction in Na+ uptake in fish reared in acidic water (pH ~4.0). A role for NHE in Na+ uptake was further confirmed by translational knockdown of NHE3b, an isoform of NHE thought to be responsible for Na+/H+ exchange in zebrafish larvae. Exposing the larvae reared in acidic water to 5 mM external ammonium sulfate or increasing the buffering capacity of the water with 10 mM HEPES caused concurrent reductions in ammonia excretion and Na+ uptake. Furthermore, translational knockdown of Rhcg1 significantly reduced ammonia excretion and Na+ uptake in larvae chronically (4 days) or acutely (24 h) exposed to acidic water. Unlike in sham-injected larvae, EIPA did not affect Na+ uptake in fish experiencing Rhcg1 knockdown. Additionally, exposure of larvae to bafilomycin A1 (an inhibitor of H+-ATPase) significantly reduced Na+ uptake in fish reared in acidic water. These observations suggest the existence of multiple mechanisms of Na+ uptake in larval zebrafish in acidic water; one in which Na+ uptake via NHE3b is linked to ammonia excretion via Rhcg1 and another facilitated by H+-ATPase.