To investigate whether Na + uptake by zebrafish is dependent on NH 4 + excretion, a scanning ion-selective electrode technique was applied to measure Na + and NH 4 + gradients at the yolk-sac surface of zebrafish larvae. Low-Na + acclimation induced an inward Na + gradient (uptake), and a combination of low Na + and high NH 4 + induced a larger inward Na + gradient. When measuring the ionic gradients, raising the external NH 4 + level (5 mM) blocked NH 4 + excretion and Na + uptake; in contrast, raising the external Na + level (10 mM) simultaneously enhanced Na + uptake and NH 4 + excretion. The addition of MOPS buffer (5 mM), which is known to block NH 4 + excretion, also suppressed Na + uptake. These results showed that Na + uptake and NH 4 + excretion by larval skin are associated when ambient Na + level is low. Knockdown of Rhcg1 translation with morpholino-oligonucleotides decreased both NH 4 + excretion and Na + uptake by the skin and Na + content of whole larvae. Knockdown of nhe3b translation or inhibitor (5-ethylisopropyl amiloride) treatment also decreased both the NH 4 + excretion and Na + uptake. This study provides loss-offunction evidence for the involvement of Rhcg1 and NHE3b in the ammonium-dependent Na + uptake mechanism in zebrafish larvae subjected to low-Na + water.
|期刊||American Journal of Physiology - Regulatory Integrative and Comparative Physiology|
|出版狀態||已發佈 - 一月 2012|
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