Stimulation of NHE3 in OKP Cells by an Autocrine Mechanism

Background/Aims: Chronic hypokalemia increases NHE3 activity in OKP cells. The aim of the present study was to determine whether an autocrine mechanism is involved in this activation. Methods: After incubation of OKP cells in normal-K+ and low-K+ media for 24 h, the potassium concentration in the low-K+ media was adjusted to a normal level. These conditioned media were then used as the normal-K+ and low-K+ supernatants. Other OKP cells were incubated in these normal-K+ and low-K+ supernatants and the mechanism of Na+/H+ antiporter activation was examined. Results: The EIPA-resistant Na+/H+ antiporter activity of OKP cells increased after 4 h incubation in the low-K+ supernatant, and the amount of NHE3 protein increased at 24 h. Since both BQ788 and saralasin blocked this antiporter activation, the supernatant concentration of endothelin I (ET-I) and angiotensin II (Ang-II) were measured. The ET-I concentration was reduced, but the Ang-II concentration remained unchanged. There was a significant association between a reduction in the ET-I concentration and an increase in Na+/H+ antiporter activity, but only when Ang-II was present in the supernatant. Conclusion: An autocrine mechanism is involved in the activation of NHE3 in OKP cells. Both ET-I and Ang-II play a role in this activation.