We have previously demonstrated that K-depletion inhibited ROMK-like small conductance K channels (SK) in the cortical collecting duct (CCD) and that the effect was mediated by superoxide anions which stimulated Src family protein tyrosine kinase (PTK) and mitogen-activated protein kinase (MAPK) (35). However, because animals on a K-deficient diet had a severe hypokalemia, superoxide-dependent signaling may not regulate ROMK channels under physiological conditions with a normal plasma K concentration. In the present study we used the patch-clamp technique and Western blot to examine the effect of low K intake (LK, 0.1 %) on ROMK channels and the role of PTK and MAPK in regulating apical K channels in the CCD of animals on a LK diet. Rats and mice on a LK diet for 7 days had a normal plasma K concentration. However, patch-clamp experiments demonstrated that LK intake decreased the probability of finding SK channels and channel activity defined by NP(o) (a product of channel number and open probability) in the CCD of both rat and mouse kidneys. Also, LK intake significantly stimulated the production of superoxide anions in the renal cortex and outer medulla (OM) in both rats and mice and increased the phosphorylation of p38 and ERK, the expression of c-Src and tyrosine phosphorylation of ROMK channels. Inhibiting p38 and ERK with SB202190 and PD98059 significantly stimulated SK in the CCD in rats on a LK diet. In addition, inhibition of PTK with Herbimycin A stimulated SK channels in the CCD from rats on a LK diet. We conclude that LK intake stimulates the generation of superoxide anion and related products and that MAPK and Src family PTK play a physiological role in inhibiting apical K channels in the principal cells in response to LK intake.