Angiotensin II modulates the activity of the Na+/K+ATPase in eel kidney

We have previously shown that angiotensin II (Ang II) has a role at the level of the eel gill chloride cell regulating sodium balance, and therefore osmoregulation; the purpose of the present study was to extend these findings to another important osmoregulatory organ, the kidney. By catalytic histochemistry Na+/K(+)ATPase activity was found in both sea water (SW)- and freshwater (FW)adapted eel kidney, particularly at the level of both proximal and distal tubules. Quantitation of tubular cell Na+/K(+)ATPase activity, by imaging, gave values in SW-adapted eels which were double those found in FW-adapted eels (Student's t-test: P 0.05 respectively). Isolated tubule cells stimulated with 100 nM Ang II showed a significant generation of inositol trisphosphate (InsP(3)) and an increment in calcium release from intracellular stores. In conclusion, our results suggest that tubular Na+/K(+)ATPase is modulated by environmental salinity, and that Ang II has a role in regulating its activity in FW-adapted eels, probably through an InsP(3)-dependent mechanism