Protein tyrosine kinase regulates the number of renal secretory K channels

The apical small conductance (SK) channel plays a key role in K secretion in the cortical collecting duct (CCD). A high-K intake stimulates renal K secretion and involves a significant increase in the number of SK channels in the apical membrane of the CCD. We used the patch-clamp technique to examine the role of protein tyrosine kinase (PTK) in regulating the activity of SK channels in the CCD. The application of 100 mu M genistein stimulated SK channels in 11 of 12 patches in CCDs from rats on a K-deficient diet, and the mean increase in NP(0), a product of channel number (N) end open probability (P(0)), was 2.5. In contrast, inhibition of PTK had no effect in tubules from animals on a high-K diet in all 10 experiments. Western blot analysis further shows that the level of cSrc, a nonreceptor type of PTK is 261% higher in the kidneys from rats on a K-deficient diet than those on a high-K diet. However, the effect of cSrc was not the result of direct inhibition of channel itself, because addition elf exogenous cSrc had no effect on SK channels in inside-out patches. In cell-attached patches, application of herbimycin A increased channel activity in 14 of 16 patches, and the mean increase in NP(0) was 2.4 in tubules from rats on a K-deficient diet. In contrast, herbimycin A had no effect on channel activity in any of 15 tubules from rats on a high-K diet. Furthermore, herbimycin A pretreatment increased NP(0) per patch from the control value (0.4) to 2.25 in CCDs from rats on a K-deficient diet, whereas herbimycin failed to increase channel activity (NP(0): control, 3.10; herbimycin A, 3.25) in the CCDs from animals on a high-K diet. We conclude that PTK is involved in regulating the number of apical SK channels in the kidney.